forked from OSchip/llvm-project
2107 lines
78 KiB
C++
2107 lines
78 KiB
C++
//===- PeepholeOptimizer.cpp - Peephole Optimizations ---------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Perform peephole optimizations on the machine code:
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//
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// - Optimize Extensions
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//
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// Optimization of sign / zero extension instructions. It may be extended to
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// handle other instructions with similar properties.
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//
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// On some targets, some instructions, e.g. X86 sign / zero extension, may
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// leave the source value in the lower part of the result. This optimization
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// will replace some uses of the pre-extension value with uses of the
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// sub-register of the results.
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//
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// - Optimize Comparisons
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//
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// Optimization of comparison instructions. For instance, in this code:
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//
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// sub r1, 1
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// cmp r1, 0
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// bz L1
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//
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// If the "sub" instruction all ready sets (or could be modified to set) the
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// same flag that the "cmp" instruction sets and that "bz" uses, then we can
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// eliminate the "cmp" instruction.
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//
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// Another instance, in this code:
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//
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// sub r1, r3 | sub r1, imm
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// cmp r3, r1 or cmp r1, r3 | cmp r1, imm
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// bge L1
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//
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// If the branch instruction can use flag from "sub", then we can replace
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// "sub" with "subs" and eliminate the "cmp" instruction.
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//
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// - Optimize Loads:
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//
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// Loads that can be folded into a later instruction. A load is foldable
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// if it loads to virtual registers and the virtual register defined has
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// a single use.
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//
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// - Optimize Copies and Bitcast (more generally, target specific copies):
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//
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// Rewrite copies and bitcasts to avoid cross register bank copies
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// when possible.
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// E.g., Consider the following example, where capital and lower
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// letters denote different register file:
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// b = copy A <-- cross-bank copy
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// C = copy b <-- cross-bank copy
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// =>
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// b = copy A <-- cross-bank copy
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// C = copy A <-- same-bank copy
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//
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// E.g., for bitcast:
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// b = bitcast A <-- cross-bank copy
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// C = bitcast b <-- cross-bank copy
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// =>
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// b = bitcast A <-- cross-bank copy
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// C = copy A <-- same-bank copy
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/CodeGen/MachineDominators.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineLoopInfo.h"
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#include "llvm/CodeGen/MachineOperand.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/TargetInstrInfo.h"
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#include "llvm/CodeGen/TargetOpcodes.h"
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#include "llvm/CodeGen/TargetRegisterInfo.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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#include "llvm/MC/LaneBitmask.h"
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#include "llvm/MC/MCInstrDesc.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include <cassert>
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#include <cstdint>
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#include <memory>
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#include <utility>
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using namespace llvm;
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using RegSubRegPair = TargetInstrInfo::RegSubRegPair;
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using RegSubRegPairAndIdx = TargetInstrInfo::RegSubRegPairAndIdx;
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#define DEBUG_TYPE "peephole-opt"
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// Optimize Extensions
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static cl::opt<bool>
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Aggressive("aggressive-ext-opt", cl::Hidden,
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cl::desc("Aggressive extension optimization"));
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static cl::opt<bool>
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DisablePeephole("disable-peephole", cl::Hidden, cl::init(false),
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cl::desc("Disable the peephole optimizer"));
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/// Specifiy whether or not the value tracking looks through
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/// complex instructions. When this is true, the value tracker
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/// bails on everything that is not a copy or a bitcast.
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static cl::opt<bool>
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DisableAdvCopyOpt("disable-adv-copy-opt", cl::Hidden, cl::init(false),
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cl::desc("Disable advanced copy optimization"));
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static cl::opt<bool> DisableNAPhysCopyOpt(
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"disable-non-allocatable-phys-copy-opt", cl::Hidden, cl::init(false),
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cl::desc("Disable non-allocatable physical register copy optimization"));
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// Limit the number of PHI instructions to process
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// in PeepholeOptimizer::getNextSource.
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static cl::opt<unsigned> RewritePHILimit(
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"rewrite-phi-limit", cl::Hidden, cl::init(10),
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cl::desc("Limit the length of PHI chains to lookup"));
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// Limit the length of recurrence chain when evaluating the benefit of
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// commuting operands.
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static cl::opt<unsigned> MaxRecurrenceChain(
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"recurrence-chain-limit", cl::Hidden, cl::init(3),
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cl::desc("Maximum length of recurrence chain when evaluating the benefit "
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"of commuting operands"));
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STATISTIC(NumReuse, "Number of extension results reused");
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STATISTIC(NumCmps, "Number of compares eliminated");
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STATISTIC(NumImmFold, "Number of move immediate folded");
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STATISTIC(NumLoadFold, "Number of loads folded");
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STATISTIC(NumSelects, "Number of selects optimized");
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STATISTIC(NumUncoalescableCopies, "Number of uncoalescable copies optimized");
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STATISTIC(NumRewrittenCopies, "Number of copies rewritten");
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STATISTIC(NumNAPhysCopies, "Number of non-allocatable physical copies removed");
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namespace {
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class ValueTrackerResult;
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class RecurrenceInstr;
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class PeepholeOptimizer : public MachineFunctionPass {
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const TargetInstrInfo *TII;
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const TargetRegisterInfo *TRI;
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MachineRegisterInfo *MRI;
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MachineDominatorTree *DT; // Machine dominator tree
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MachineLoopInfo *MLI;
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public:
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static char ID; // Pass identification
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PeepholeOptimizer() : MachineFunctionPass(ID) {
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initializePeepholeOptimizerPass(*PassRegistry::getPassRegistry());
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}
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bool runOnMachineFunction(MachineFunction &MF) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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MachineFunctionPass::getAnalysisUsage(AU);
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AU.addRequired<MachineLoopInfo>();
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AU.addPreserved<MachineLoopInfo>();
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if (Aggressive) {
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AU.addRequired<MachineDominatorTree>();
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AU.addPreserved<MachineDominatorTree>();
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}
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}
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/// Track Def -> Use info used for rewriting copies.
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using RewriteMapTy = SmallDenseMap<RegSubRegPair, ValueTrackerResult>;
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/// Sequence of instructions that formulate recurrence cycle.
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using RecurrenceCycle = SmallVector<RecurrenceInstr, 4>;
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private:
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bool optimizeCmpInstr(MachineInstr &MI);
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bool optimizeExtInstr(MachineInstr &MI, MachineBasicBlock &MBB,
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SmallPtrSetImpl<MachineInstr*> &LocalMIs);
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bool optimizeSelect(MachineInstr &MI,
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SmallPtrSetImpl<MachineInstr *> &LocalMIs);
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bool optimizeCondBranch(MachineInstr &MI);
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bool optimizeCoalescableCopy(MachineInstr &MI);
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bool optimizeUncoalescableCopy(MachineInstr &MI,
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SmallPtrSetImpl<MachineInstr *> &LocalMIs);
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bool optimizeRecurrence(MachineInstr &PHI);
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bool findNextSource(RegSubRegPair RegSubReg, RewriteMapTy &RewriteMap);
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bool isMoveImmediate(MachineInstr &MI,
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SmallSet<unsigned, 4> &ImmDefRegs,
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DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
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bool foldImmediate(MachineInstr &MI, SmallSet<unsigned, 4> &ImmDefRegs,
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DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
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/// \brief Finds recurrence cycles, but only ones that formulated around
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/// a def operand and a use operand that are tied. If there is a use
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/// operand commutable with the tied use operand, find recurrence cycle
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/// along that operand as well.
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bool findTargetRecurrence(unsigned Reg,
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const SmallSet<unsigned, 2> &TargetReg,
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RecurrenceCycle &RC);
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/// \brief If copy instruction \p MI is a virtual register copy, track it in
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/// the set \p CopySrcRegs and \p CopyMIs. If this virtual register was
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/// previously seen as a copy, replace the uses of this copy with the
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/// previously seen copy's destination register.
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bool foldRedundantCopy(MachineInstr &MI,
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SmallSet<unsigned, 4> &CopySrcRegs,
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DenseMap<unsigned, MachineInstr *> &CopyMIs);
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/// Is the register \p Reg a non-allocatable physical register?
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bool isNAPhysCopy(unsigned Reg);
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/// \brief If copy instruction \p MI is a non-allocatable virtual<->physical
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/// register copy, track it in the \p NAPhysToVirtMIs map. If this
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/// non-allocatable physical register was previously copied to a virtual
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/// registered and hasn't been clobbered, the virt->phys copy can be
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/// deleted.
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bool foldRedundantNAPhysCopy(MachineInstr &MI,
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DenseMap<unsigned, MachineInstr *> &NAPhysToVirtMIs);
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bool isLoadFoldable(MachineInstr &MI,
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SmallSet<unsigned, 16> &FoldAsLoadDefCandidates);
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/// \brief Check whether \p MI is understood by the register coalescer
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/// but may require some rewriting.
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bool isCoalescableCopy(const MachineInstr &MI) {
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// SubregToRegs are not interesting, because they are already register
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// coalescer friendly.
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return MI.isCopy() || (!DisableAdvCopyOpt &&
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(MI.isRegSequence() || MI.isInsertSubreg() ||
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MI.isExtractSubreg()));
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}
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/// \brief Check whether \p MI is a copy like instruction that is
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/// not recognized by the register coalescer.
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bool isUncoalescableCopy(const MachineInstr &MI) {
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return MI.isBitcast() ||
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(!DisableAdvCopyOpt &&
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(MI.isRegSequenceLike() || MI.isInsertSubregLike() ||
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MI.isExtractSubregLike()));
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}
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MachineInstr &rewriteSource(MachineInstr &CopyLike,
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RegSubRegPair Def, RewriteMapTy &RewriteMap);
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};
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/// Helper class to hold instructions that are inside recurrence cycles.
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/// The recurrence cycle is formulated around 1) a def operand and its
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/// tied use operand, or 2) a def operand and a use operand that is commutable
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/// with another use operand which is tied to the def operand. In the latter
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/// case, index of the tied use operand and the commutable use operand are
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/// maintained with CommutePair.
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class RecurrenceInstr {
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public:
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using IndexPair = std::pair<unsigned, unsigned>;
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RecurrenceInstr(MachineInstr *MI) : MI(MI) {}
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RecurrenceInstr(MachineInstr *MI, unsigned Idx1, unsigned Idx2)
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: MI(MI), CommutePair(std::make_pair(Idx1, Idx2)) {}
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MachineInstr *getMI() const { return MI; }
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Optional<IndexPair> getCommutePair() const { return CommutePair; }
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private:
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MachineInstr *MI;
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Optional<IndexPair> CommutePair;
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};
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/// Helper class to hold a reply for ValueTracker queries.
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/// Contains the returned sources for a given search and the instructions
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/// where the sources were tracked from.
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class ValueTrackerResult {
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private:
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/// Track all sources found by one ValueTracker query.
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SmallVector<RegSubRegPair, 2> RegSrcs;
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/// Instruction using the sources in 'RegSrcs'.
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const MachineInstr *Inst = nullptr;
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public:
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ValueTrackerResult() = default;
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ValueTrackerResult(unsigned Reg, unsigned SubReg) {
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addSource(Reg, SubReg);
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}
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bool isValid() const { return getNumSources() > 0; }
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void setInst(const MachineInstr *I) { Inst = I; }
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const MachineInstr *getInst() const { return Inst; }
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void clear() {
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RegSrcs.clear();
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Inst = nullptr;
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}
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void addSource(unsigned SrcReg, unsigned SrcSubReg) {
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RegSrcs.push_back(RegSubRegPair(SrcReg, SrcSubReg));
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}
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void setSource(int Idx, unsigned SrcReg, unsigned SrcSubReg) {
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assert(Idx < getNumSources() && "Reg pair source out of index");
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RegSrcs[Idx] = RegSubRegPair(SrcReg, SrcSubReg);
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}
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int getNumSources() const { return RegSrcs.size(); }
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RegSubRegPair getSrc(int Idx) const {
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return RegSrcs[Idx];
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}
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unsigned getSrcReg(int Idx) const {
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assert(Idx < getNumSources() && "Reg source out of index");
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return RegSrcs[Idx].Reg;
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}
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unsigned getSrcSubReg(int Idx) const {
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assert(Idx < getNumSources() && "SubReg source out of index");
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return RegSrcs[Idx].SubReg;
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}
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bool operator==(const ValueTrackerResult &Other) {
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if (Other.getInst() != getInst())
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return false;
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if (Other.getNumSources() != getNumSources())
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return false;
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for (int i = 0, e = Other.getNumSources(); i != e; ++i)
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if (Other.getSrcReg(i) != getSrcReg(i) ||
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Other.getSrcSubReg(i) != getSrcSubReg(i))
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return false;
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return true;
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}
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};
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/// \brief Helper class to track the possible sources of a value defined by
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/// a (chain of) copy related instructions.
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/// Given a definition (instruction and definition index), this class
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/// follows the use-def chain to find successive suitable sources.
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/// The given source can be used to rewrite the definition into
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/// def = COPY src.
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///
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/// For instance, let us consider the following snippet:
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/// v0 =
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/// v2 = INSERT_SUBREG v1, v0, sub0
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/// def = COPY v2.sub0
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///
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/// Using a ValueTracker for def = COPY v2.sub0 will give the following
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/// suitable sources:
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/// v2.sub0 and v0.
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/// Then, def can be rewritten into def = COPY v0.
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class ValueTracker {
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private:
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/// The current point into the use-def chain.
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const MachineInstr *Def = nullptr;
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/// The index of the definition in Def.
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unsigned DefIdx = 0;
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/// The sub register index of the definition.
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unsigned DefSubReg;
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/// The register where the value can be found.
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unsigned Reg;
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/// MachineRegisterInfo used to perform tracking.
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const MachineRegisterInfo &MRI;
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/// Optional TargetInstrInfo used to perform some complex tracking.
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const TargetInstrInfo *TII;
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/// Dispatcher to the right underlying implementation of getNextSource.
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ValueTrackerResult getNextSourceImpl();
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/// Specialized version of getNextSource for Copy instructions.
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ValueTrackerResult getNextSourceFromCopy();
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/// Specialized version of getNextSource for Bitcast instructions.
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ValueTrackerResult getNextSourceFromBitcast();
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/// Specialized version of getNextSource for RegSequence instructions.
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ValueTrackerResult getNextSourceFromRegSequence();
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/// Specialized version of getNextSource for InsertSubreg instructions.
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ValueTrackerResult getNextSourceFromInsertSubreg();
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/// Specialized version of getNextSource for ExtractSubreg instructions.
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ValueTrackerResult getNextSourceFromExtractSubreg();
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/// Specialized version of getNextSource for SubregToReg instructions.
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ValueTrackerResult getNextSourceFromSubregToReg();
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/// Specialized version of getNextSource for PHI instructions.
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ValueTrackerResult getNextSourceFromPHI();
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public:
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/// Create a ValueTracker instance for the value defined by \p Reg.
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/// \p DefSubReg represents the sub register index the value tracker will
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/// track. It does not need to match the sub register index used in the
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/// definition of \p Reg.
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/// If \p Reg is a physical register, a value tracker constructed with
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/// this constructor will not find any alternative source.
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/// Indeed, when \p Reg is a physical register that constructor does not
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/// know which definition of \p Reg it should track.
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/// Use the next constructor to track a physical register.
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ValueTracker(unsigned Reg, unsigned DefSubReg,
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const MachineRegisterInfo &MRI,
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const TargetInstrInfo *TII = nullptr)
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: DefSubReg(DefSubReg), Reg(Reg), MRI(MRI), TII(TII) {
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if (!TargetRegisterInfo::isPhysicalRegister(Reg)) {
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Def = MRI.getVRegDef(Reg);
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DefIdx = MRI.def_begin(Reg).getOperandNo();
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}
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}
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/// \brief Following the use-def chain, get the next available source
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/// for the tracked value.
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/// \return A ValueTrackerResult containing a set of registers
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/// and sub registers with tracked values. A ValueTrackerResult with
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/// an empty set of registers means no source was found.
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ValueTrackerResult getNextSource();
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};
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} // end anonymous namespace
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char PeepholeOptimizer::ID = 0;
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char &llvm::PeepholeOptimizerID = PeepholeOptimizer::ID;
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INITIALIZE_PASS_BEGIN(PeepholeOptimizer, DEBUG_TYPE,
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"Peephole Optimizations", false, false)
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INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
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INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
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INITIALIZE_PASS_END(PeepholeOptimizer, DEBUG_TYPE,
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"Peephole Optimizations", false, false)
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/// If instruction is a copy-like instruction, i.e. it reads a single register
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/// and writes a single register and it does not modify the source, and if the
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/// source value is preserved as a sub-register of the result, then replace all
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/// reachable uses of the source with the subreg of the result.
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///
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/// Do not generate an EXTRACT that is used only in a debug use, as this changes
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/// the code. Since this code does not currently share EXTRACTs, just ignore all
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/// debug uses.
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bool PeepholeOptimizer::
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optimizeExtInstr(MachineInstr &MI, MachineBasicBlock &MBB,
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SmallPtrSetImpl<MachineInstr*> &LocalMIs) {
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unsigned SrcReg, DstReg, SubIdx;
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if (!TII->isCoalescableExtInstr(MI, SrcReg, DstReg, SubIdx))
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return false;
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if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
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TargetRegisterInfo::isPhysicalRegister(SrcReg))
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return false;
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if (MRI->hasOneNonDBGUse(SrcReg))
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// No other uses.
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return false;
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// Ensure DstReg can get a register class that actually supports
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// sub-registers. Don't change the class until we commit.
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const TargetRegisterClass *DstRC = MRI->getRegClass(DstReg);
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DstRC = TRI->getSubClassWithSubReg(DstRC, SubIdx);
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if (!DstRC)
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return false;
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// The ext instr may be operating on a sub-register of SrcReg as well.
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// PPC::EXTSW is a 32 -> 64-bit sign extension, but it reads a 64-bit
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// register.
|
|
// If UseSrcSubIdx is Set, SubIdx also applies to SrcReg, and only uses of
|
|
// SrcReg:SubIdx should be replaced.
|
|
bool UseSrcSubIdx =
|
|
TRI->getSubClassWithSubReg(MRI->getRegClass(SrcReg), SubIdx) != nullptr;
|
|
|
|
// The source has other uses. See if we can replace the other uses with use of
|
|
// the result of the extension.
|
|
SmallPtrSet<MachineBasicBlock*, 4> ReachedBBs;
|
|
for (MachineInstr &UI : MRI->use_nodbg_instructions(DstReg))
|
|
ReachedBBs.insert(UI.getParent());
|
|
|
|
// Uses that are in the same BB of uses of the result of the instruction.
|
|
SmallVector<MachineOperand*, 8> Uses;
|
|
|
|
// Uses that the result of the instruction can reach.
|
|
SmallVector<MachineOperand*, 8> ExtendedUses;
|
|
|
|
bool ExtendLife = true;
|
|
for (MachineOperand &UseMO : MRI->use_nodbg_operands(SrcReg)) {
|
|
MachineInstr *UseMI = UseMO.getParent();
|
|
if (UseMI == &MI)
|
|
continue;
|
|
|
|
if (UseMI->isPHI()) {
|
|
ExtendLife = false;
|
|
continue;
|
|
}
|
|
|
|
// Only accept uses of SrcReg:SubIdx.
|
|
if (UseSrcSubIdx && UseMO.getSubReg() != SubIdx)
|
|
continue;
|
|
|
|
// It's an error to translate this:
|
|
//
|
|
// %reg1025 = <sext> %reg1024
|
|
// ...
|
|
// %reg1026 = SUBREG_TO_REG 0, %reg1024, 4
|
|
//
|
|
// into this:
|
|
//
|
|
// %reg1025 = <sext> %reg1024
|
|
// ...
|
|
// %reg1027 = COPY %reg1025:4
|
|
// %reg1026 = SUBREG_TO_REG 0, %reg1027, 4
|
|
//
|
|
// The problem here is that SUBREG_TO_REG is there to assert that an
|
|
// implicit zext occurs. It doesn't insert a zext instruction. If we allow
|
|
// the COPY here, it will give us the value after the <sext>, not the
|
|
// original value of %reg1024 before <sext>.
|
|
if (UseMI->getOpcode() == TargetOpcode::SUBREG_TO_REG)
|
|
continue;
|
|
|
|
MachineBasicBlock *UseMBB = UseMI->getParent();
|
|
if (UseMBB == &MBB) {
|
|
// Local uses that come after the extension.
|
|
if (!LocalMIs.count(UseMI))
|
|
Uses.push_back(&UseMO);
|
|
} else if (ReachedBBs.count(UseMBB)) {
|
|
// Non-local uses where the result of the extension is used. Always
|
|
// replace these unless it's a PHI.
|
|
Uses.push_back(&UseMO);
|
|
} else if (Aggressive && DT->dominates(&MBB, UseMBB)) {
|
|
// We may want to extend the live range of the extension result in order
|
|
// to replace these uses.
|
|
ExtendedUses.push_back(&UseMO);
|
|
} else {
|
|
// Both will be live out of the def MBB anyway. Don't extend live range of
|
|
// the extension result.
|
|
ExtendLife = false;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (ExtendLife && !ExtendedUses.empty())
|
|
// Extend the liveness of the extension result.
|
|
Uses.append(ExtendedUses.begin(), ExtendedUses.end());
|
|
|
|
// Now replace all uses.
|
|
bool Changed = false;
|
|
if (!Uses.empty()) {
|
|
SmallPtrSet<MachineBasicBlock*, 4> PHIBBs;
|
|
|
|
// Look for PHI uses of the extended result, we don't want to extend the
|
|
// liveness of a PHI input. It breaks all kinds of assumptions down
|
|
// stream. A PHI use is expected to be the kill of its source values.
|
|
for (MachineInstr &UI : MRI->use_nodbg_instructions(DstReg))
|
|
if (UI.isPHI())
|
|
PHIBBs.insert(UI.getParent());
|
|
|
|
const TargetRegisterClass *RC = MRI->getRegClass(SrcReg);
|
|
for (unsigned i = 0, e = Uses.size(); i != e; ++i) {
|
|
MachineOperand *UseMO = Uses[i];
|
|
MachineInstr *UseMI = UseMO->getParent();
|
|
MachineBasicBlock *UseMBB = UseMI->getParent();
|
|
if (PHIBBs.count(UseMBB))
|
|
continue;
|
|
|
|
// About to add uses of DstReg, clear DstReg's kill flags.
|
|
if (!Changed) {
|
|
MRI->clearKillFlags(DstReg);
|
|
MRI->constrainRegClass(DstReg, DstRC);
|
|
}
|
|
|
|
unsigned NewVR = MRI->createVirtualRegister(RC);
|
|
MachineInstr *Copy = BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
|
|
TII->get(TargetOpcode::COPY), NewVR)
|
|
.addReg(DstReg, 0, SubIdx);
|
|
// SubIdx applies to both SrcReg and DstReg when UseSrcSubIdx is set.
|
|
if (UseSrcSubIdx) {
|
|
Copy->getOperand(0).setSubReg(SubIdx);
|
|
Copy->getOperand(0).setIsUndef();
|
|
}
|
|
UseMO->setReg(NewVR);
|
|
++NumReuse;
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
/// If the instruction is a compare and the previous instruction it's comparing
|
|
/// against already sets (or could be modified to set) the same flag as the
|
|
/// compare, then we can remove the comparison and use the flag from the
|
|
/// previous instruction.
|
|
bool PeepholeOptimizer::optimizeCmpInstr(MachineInstr &MI) {
|
|
// If this instruction is a comparison against zero and isn't comparing a
|
|
// physical register, we can try to optimize it.
|
|
unsigned SrcReg, SrcReg2;
|
|
int CmpMask, CmpValue;
|
|
if (!TII->analyzeCompare(MI, SrcReg, SrcReg2, CmpMask, CmpValue) ||
|
|
TargetRegisterInfo::isPhysicalRegister(SrcReg) ||
|
|
(SrcReg2 != 0 && TargetRegisterInfo::isPhysicalRegister(SrcReg2)))
|
|
return false;
|
|
|
|
// Attempt to optimize the comparison instruction.
|
|
if (TII->optimizeCompareInstr(MI, SrcReg, SrcReg2, CmpMask, CmpValue, MRI)) {
|
|
++NumCmps;
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Optimize a select instruction.
|
|
bool PeepholeOptimizer::optimizeSelect(MachineInstr &MI,
|
|
SmallPtrSetImpl<MachineInstr *> &LocalMIs) {
|
|
unsigned TrueOp = 0;
|
|
unsigned FalseOp = 0;
|
|
bool Optimizable = false;
|
|
SmallVector<MachineOperand, 4> Cond;
|
|
if (TII->analyzeSelect(MI, Cond, TrueOp, FalseOp, Optimizable))
|
|
return false;
|
|
if (!Optimizable)
|
|
return false;
|
|
if (!TII->optimizeSelect(MI, LocalMIs))
|
|
return false;
|
|
MI.eraseFromParent();
|
|
++NumSelects;
|
|
return true;
|
|
}
|
|
|
|
/// Check if a simpler conditional branch can be generated.
|
|
bool PeepholeOptimizer::optimizeCondBranch(MachineInstr &MI) {
|
|
return TII->optimizeCondBranch(MI);
|
|
}
|
|
|
|
/// \brief Try to find the next source that share the same register file
|
|
/// for the value defined by \p Reg and \p SubReg.
|
|
/// When true is returned, the \p RewriteMap can be used by the client to
|
|
/// retrieve all Def -> Use along the way up to the next source. Any found
|
|
/// Use that is not itself a key for another entry, is the next source to
|
|
/// use. During the search for the next source, multiple sources can be found
|
|
/// given multiple incoming sources of a PHI instruction. In this case, we
|
|
/// look in each PHI source for the next source; all found next sources must
|
|
/// share the same register file as \p Reg and \p SubReg. The client should
|
|
/// then be capable to rewrite all intermediate PHIs to get the next source.
|
|
/// \return False if no alternative sources are available. True otherwise.
|
|
bool PeepholeOptimizer::findNextSource(RegSubRegPair RegSubReg,
|
|
RewriteMapTy &RewriteMap) {
|
|
// Do not try to find a new source for a physical register.
|
|
// So far we do not have any motivating example for doing that.
|
|
// Thus, instead of maintaining untested code, we will revisit that if
|
|
// that changes at some point.
|
|
unsigned Reg = RegSubReg.Reg;
|
|
if (TargetRegisterInfo::isPhysicalRegister(Reg))
|
|
return false;
|
|
const TargetRegisterClass *DefRC = MRI->getRegClass(Reg);
|
|
|
|
SmallVector<RegSubRegPair, 4> SrcToLook;
|
|
RegSubRegPair CurSrcPair = RegSubReg;
|
|
SrcToLook.push_back(CurSrcPair);
|
|
|
|
unsigned PHICount = 0;
|
|
do {
|
|
CurSrcPair = SrcToLook.pop_back_val();
|
|
// As explained above, do not handle physical registers
|
|
if (TargetRegisterInfo::isPhysicalRegister(CurSrcPair.Reg))
|
|
return false;
|
|
|
|
ValueTracker ValTracker(CurSrcPair.Reg, CurSrcPair.SubReg, *MRI, TII);
|
|
|
|
// Follow the chain of copies until we find a more suitable source, a phi
|
|
// or have to abort.
|
|
while (true) {
|
|
ValueTrackerResult Res = ValTracker.getNextSource();
|
|
// Abort at the end of a chain (without finding a suitable source).
|
|
if (!Res.isValid())
|
|
return false;
|
|
|
|
// Insert the Def -> Use entry for the recently found source.
|
|
ValueTrackerResult CurSrcRes = RewriteMap.lookup(CurSrcPair);
|
|
if (CurSrcRes.isValid()) {
|
|
assert(CurSrcRes == Res && "ValueTrackerResult found must match");
|
|
// An existent entry with multiple sources is a PHI cycle we must avoid.
|
|
// Otherwise it's an entry with a valid next source we already found.
|
|
if (CurSrcRes.getNumSources() > 1) {
|
|
DEBUG(dbgs() << "findNextSource: found PHI cycle, aborting...\n");
|
|
return false;
|
|
}
|
|
break;
|
|
}
|
|
RewriteMap.insert(std::make_pair(CurSrcPair, Res));
|
|
|
|
// ValueTrackerResult usually have one source unless it's the result from
|
|
// a PHI instruction. Add the found PHI edges to be looked up further.
|
|
unsigned NumSrcs = Res.getNumSources();
|
|
if (NumSrcs > 1) {
|
|
PHICount++;
|
|
if (PHICount >= RewritePHILimit) {
|
|
DEBUG(dbgs() << "findNextSource: PHI limit reached\n");
|
|
return false;
|
|
}
|
|
|
|
for (unsigned i = 0; i < NumSrcs; ++i)
|
|
SrcToLook.push_back(Res.getSrc(i));
|
|
break;
|
|
}
|
|
|
|
CurSrcPair = Res.getSrc(0);
|
|
// Do not extend the live-ranges of physical registers as they add
|
|
// constraints to the register allocator. Moreover, if we want to extend
|
|
// the live-range of a physical register, unlike SSA virtual register,
|
|
// we will have to check that they aren't redefine before the related use.
|
|
if (TargetRegisterInfo::isPhysicalRegister(CurSrcPair.Reg))
|
|
return false;
|
|
|
|
// Keep following the chain if the value isn't any better yet.
|
|
const TargetRegisterClass *SrcRC = MRI->getRegClass(CurSrcPair.Reg);
|
|
if (!TRI->shouldRewriteCopySrc(DefRC, RegSubReg.SubReg, SrcRC,
|
|
CurSrcPair.SubReg))
|
|
continue;
|
|
|
|
// We currently cannot deal with subreg operands on PHI instructions
|
|
// (see insertPHI()).
|
|
if (PHICount > 0 && CurSrcPair.SubReg != 0)
|
|
continue;
|
|
|
|
// We found a suitable source, and are done with this chain.
|
|
break;
|
|
}
|
|
} while (!SrcToLook.empty());
|
|
|
|
// If we did not find a more suitable source, there is nothing to optimize.
|
|
return CurSrcPair.Reg != Reg;
|
|
}
|
|
|
|
/// \brief Insert a PHI instruction with incoming edges \p SrcRegs that are
|
|
/// guaranteed to have the same register class. This is necessary whenever we
|
|
/// successfully traverse a PHI instruction and find suitable sources coming
|
|
/// from its edges. By inserting a new PHI, we provide a rewritten PHI def
|
|
/// suitable to be used in a new COPY instruction.
|
|
static MachineInstr &
|
|
insertPHI(MachineRegisterInfo &MRI, const TargetInstrInfo &TII,
|
|
const SmallVectorImpl<RegSubRegPair> &SrcRegs,
|
|
MachineInstr &OrigPHI) {
|
|
assert(!SrcRegs.empty() && "No sources to create a PHI instruction?");
|
|
|
|
const TargetRegisterClass *NewRC = MRI.getRegClass(SrcRegs[0].Reg);
|
|
// NewRC is only correct if no subregisters are involved. findNextSource()
|
|
// should have rejected those cases already.
|
|
assert(SrcRegs[0].SubReg == 0 && "should not have subreg operand");
|
|
unsigned NewVR = MRI.createVirtualRegister(NewRC);
|
|
MachineBasicBlock *MBB = OrigPHI.getParent();
|
|
MachineInstrBuilder MIB = BuildMI(*MBB, &OrigPHI, OrigPHI.getDebugLoc(),
|
|
TII.get(TargetOpcode::PHI), NewVR);
|
|
|
|
unsigned MBBOpIdx = 2;
|
|
for (const RegSubRegPair &RegPair : SrcRegs) {
|
|
MIB.addReg(RegPair.Reg, 0, RegPair.SubReg);
|
|
MIB.addMBB(OrigPHI.getOperand(MBBOpIdx).getMBB());
|
|
// Since we're extended the lifetime of RegPair.Reg, clear the
|
|
// kill flags to account for that and make RegPair.Reg reaches
|
|
// the new PHI.
|
|
MRI.clearKillFlags(RegPair.Reg);
|
|
MBBOpIdx += 2;
|
|
}
|
|
|
|
return *MIB;
|
|
}
|
|
|
|
namespace {
|
|
|
|
/// Interface to query instructions amenable to copy rewriting.
|
|
class Rewriter {
|
|
protected:
|
|
MachineInstr &CopyLike;
|
|
unsigned CurrentSrcIdx = 0; ///< The index of the source being rewritten.
|
|
public:
|
|
Rewriter(MachineInstr &CopyLike) : CopyLike(CopyLike) {}
|
|
virtual ~Rewriter() {}
|
|
|
|
/// \brief Get the next rewritable source (SrcReg, SrcSubReg) and
|
|
/// the related value that it affects (DstReg, DstSubReg).
|
|
/// A source is considered rewritable if its register class and the
|
|
/// register class of the related DstReg may not be register
|
|
/// coalescer friendly. In other words, given a copy-like instruction
|
|
/// not all the arguments may be returned at rewritable source, since
|
|
/// some arguments are none to be register coalescer friendly.
|
|
///
|
|
/// Each call of this method moves the current source to the next
|
|
/// rewritable source.
|
|
/// For instance, let CopyLike be the instruction to rewrite.
|
|
/// CopyLike has one definition and one source:
|
|
/// dst.dstSubIdx = CopyLike src.srcSubIdx.
|
|
///
|
|
/// The first call will give the first rewritable source, i.e.,
|
|
/// the only source this instruction has:
|
|
/// (SrcReg, SrcSubReg) = (src, srcSubIdx).
|
|
/// This source defines the whole definition, i.e.,
|
|
/// (DstReg, DstSubReg) = (dst, dstSubIdx).
|
|
///
|
|
/// The second and subsequent calls will return false, as there is only one
|
|
/// rewritable source.
|
|
///
|
|
/// \return True if a rewritable source has been found, false otherwise.
|
|
/// The output arguments are valid if and only if true is returned.
|
|
virtual bool getNextRewritableSource(RegSubRegPair &Src,
|
|
RegSubRegPair &Dst) = 0;
|
|
|
|
/// Rewrite the current source with \p NewReg and \p NewSubReg if possible.
|
|
/// \return True if the rewriting was possible, false otherwise.
|
|
virtual bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) = 0;
|
|
};
|
|
|
|
/// Rewriter for COPY instructions.
|
|
class CopyRewriter : public Rewriter {
|
|
public:
|
|
CopyRewriter(MachineInstr &MI) : Rewriter(MI) {
|
|
assert(MI.isCopy() && "Expected copy instruction");
|
|
}
|
|
virtual ~CopyRewriter() = default;
|
|
|
|
bool getNextRewritableSource(RegSubRegPair &Src,
|
|
RegSubRegPair &Dst) override {
|
|
// CurrentSrcIdx > 0 means this function has already been called.
|
|
if (CurrentSrcIdx > 0)
|
|
return false;
|
|
// This is the first call to getNextRewritableSource.
|
|
// Move the CurrentSrcIdx to remember that we made that call.
|
|
CurrentSrcIdx = 1;
|
|
// The rewritable source is the argument.
|
|
const MachineOperand &MOSrc = CopyLike.getOperand(1);
|
|
Src = RegSubRegPair(MOSrc.getReg(), MOSrc.getSubReg());
|
|
// What we track are the alternative sources of the definition.
|
|
const MachineOperand &MODef = CopyLike.getOperand(0);
|
|
Dst = RegSubRegPair(MODef.getReg(), MODef.getSubReg());
|
|
return true;
|
|
}
|
|
|
|
bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
|
|
if (CurrentSrcIdx != 1)
|
|
return false;
|
|
MachineOperand &MOSrc = CopyLike.getOperand(CurrentSrcIdx);
|
|
MOSrc.setReg(NewReg);
|
|
MOSrc.setSubReg(NewSubReg);
|
|
return true;
|
|
}
|
|
};
|
|
|
|
/// \brief Helper class to rewrite uncoalescable copy like instructions
|
|
/// into new COPY (coalescable friendly) instructions.
|
|
class UncoalescableRewriter : public Rewriter {
|
|
unsigned NumDefs; ///< Number of defs in the bitcast.
|
|
|
|
public:
|
|
UncoalescableRewriter(MachineInstr &MI) : Rewriter(MI) {
|
|
NumDefs = MI.getDesc().getNumDefs();
|
|
}
|
|
|
|
/// \see See Rewriter::getNextRewritableSource()
|
|
/// All such sources need to be considered rewritable in order to
|
|
/// rewrite a uncoalescable copy-like instruction. This method return
|
|
/// each definition that must be checked if rewritable.
|
|
bool getNextRewritableSource(RegSubRegPair &Src,
|
|
RegSubRegPair &Dst) override {
|
|
// Find the next non-dead definition and continue from there.
|
|
if (CurrentSrcIdx == NumDefs)
|
|
return false;
|
|
|
|
while (CopyLike.getOperand(CurrentSrcIdx).isDead()) {
|
|
++CurrentSrcIdx;
|
|
if (CurrentSrcIdx == NumDefs)
|
|
return false;
|
|
}
|
|
|
|
// What we track are the alternative sources of the definition.
|
|
Src = RegSubRegPair(0, 0);
|
|
const MachineOperand &MODef = CopyLike.getOperand(CurrentSrcIdx);
|
|
Dst = RegSubRegPair(MODef.getReg(), MODef.getSubReg());
|
|
|
|
CurrentSrcIdx++;
|
|
return true;
|
|
}
|
|
|
|
bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
|
|
return false;
|
|
}
|
|
};
|
|
|
|
/// Specialized rewriter for INSERT_SUBREG instruction.
|
|
class InsertSubregRewriter : public Rewriter {
|
|
public:
|
|
InsertSubregRewriter(MachineInstr &MI) : Rewriter(MI) {
|
|
assert(MI.isInsertSubreg() && "Invalid instruction");
|
|
}
|
|
|
|
/// \see See Rewriter::getNextRewritableSource()
|
|
/// Here CopyLike has the following form:
|
|
/// dst = INSERT_SUBREG Src1, Src2.src2SubIdx, subIdx.
|
|
/// Src1 has the same register class has dst, hence, there is
|
|
/// nothing to rewrite.
|
|
/// Src2.src2SubIdx, may not be register coalescer friendly.
|
|
/// Therefore, the first call to this method returns:
|
|
/// (SrcReg, SrcSubReg) = (Src2, src2SubIdx).
|
|
/// (DstReg, DstSubReg) = (dst, subIdx).
|
|
///
|
|
/// Subsequence calls will return false.
|
|
bool getNextRewritableSource(RegSubRegPair &Src,
|
|
RegSubRegPair &Dst) override {
|
|
// If we already get the only source we can rewrite, return false.
|
|
if (CurrentSrcIdx == 2)
|
|
return false;
|
|
// We are looking at v2 = INSERT_SUBREG v0, v1, sub0.
|
|
CurrentSrcIdx = 2;
|
|
const MachineOperand &MOInsertedReg = CopyLike.getOperand(2);
|
|
Src = RegSubRegPair(MOInsertedReg.getReg(), MOInsertedReg.getSubReg());
|
|
const MachineOperand &MODef = CopyLike.getOperand(0);
|
|
|
|
// We want to track something that is compatible with the
|
|
// partial definition.
|
|
if (MODef.getSubReg())
|
|
// Bail if we have to compose sub-register indices.
|
|
return false;
|
|
Dst = RegSubRegPair(MODef.getReg(),
|
|
(unsigned)CopyLike.getOperand(3).getImm());
|
|
return true;
|
|
}
|
|
|
|
bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
|
|
if (CurrentSrcIdx != 2)
|
|
return false;
|
|
// We are rewriting the inserted reg.
|
|
MachineOperand &MO = CopyLike.getOperand(CurrentSrcIdx);
|
|
MO.setReg(NewReg);
|
|
MO.setSubReg(NewSubReg);
|
|
return true;
|
|
}
|
|
};
|
|
|
|
/// Specialized rewriter for EXTRACT_SUBREG instruction.
|
|
class ExtractSubregRewriter : public Rewriter {
|
|
const TargetInstrInfo &TII;
|
|
|
|
public:
|
|
ExtractSubregRewriter(MachineInstr &MI, const TargetInstrInfo &TII)
|
|
: Rewriter(MI), TII(TII) {
|
|
assert(MI.isExtractSubreg() && "Invalid instruction");
|
|
}
|
|
|
|
/// \see Rewriter::getNextRewritableSource()
|
|
/// Here CopyLike has the following form:
|
|
/// dst.dstSubIdx = EXTRACT_SUBREG Src, subIdx.
|
|
/// There is only one rewritable source: Src.subIdx,
|
|
/// which defines dst.dstSubIdx.
|
|
bool getNextRewritableSource(RegSubRegPair &Src,
|
|
RegSubRegPair &Dst) override {
|
|
// If we already get the only source we can rewrite, return false.
|
|
if (CurrentSrcIdx == 1)
|
|
return false;
|
|
// We are looking at v1 = EXTRACT_SUBREG v0, sub0.
|
|
CurrentSrcIdx = 1;
|
|
const MachineOperand &MOExtractedReg = CopyLike.getOperand(1);
|
|
// If we have to compose sub-register indices, bail out.
|
|
if (MOExtractedReg.getSubReg())
|
|
return false;
|
|
|
|
Src = RegSubRegPair(MOExtractedReg.getReg(),
|
|
CopyLike.getOperand(2).getImm());
|
|
|
|
// We want to track something that is compatible with the definition.
|
|
const MachineOperand &MODef = CopyLike.getOperand(0);
|
|
Dst = RegSubRegPair(MODef.getReg(), MODef.getSubReg());
|
|
return true;
|
|
}
|
|
|
|
bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
|
|
// The only source we can rewrite is the input register.
|
|
if (CurrentSrcIdx != 1)
|
|
return false;
|
|
|
|
CopyLike.getOperand(CurrentSrcIdx).setReg(NewReg);
|
|
|
|
// If we find a source that does not require to extract something,
|
|
// rewrite the operation with a copy.
|
|
if (!NewSubReg) {
|
|
// Move the current index to an invalid position.
|
|
// We do not want another call to this method to be able
|
|
// to do any change.
|
|
CurrentSrcIdx = -1;
|
|
// Rewrite the operation as a COPY.
|
|
// Get rid of the sub-register index.
|
|
CopyLike.RemoveOperand(2);
|
|
// Morph the operation into a COPY.
|
|
CopyLike.setDesc(TII.get(TargetOpcode::COPY));
|
|
return true;
|
|
}
|
|
CopyLike.getOperand(CurrentSrcIdx + 1).setImm(NewSubReg);
|
|
return true;
|
|
}
|
|
};
|
|
|
|
/// Specialized rewriter for REG_SEQUENCE instruction.
|
|
class RegSequenceRewriter : public Rewriter {
|
|
public:
|
|
RegSequenceRewriter(MachineInstr &MI) : Rewriter(MI) {
|
|
assert(MI.isRegSequence() && "Invalid instruction");
|
|
}
|
|
|
|
/// \see Rewriter::getNextRewritableSource()
|
|
/// Here CopyLike has the following form:
|
|
/// dst = REG_SEQUENCE Src1.src1SubIdx, subIdx1, Src2.src2SubIdx, subIdx2.
|
|
/// Each call will return a different source, walking all the available
|
|
/// source.
|
|
///
|
|
/// The first call returns:
|
|
/// (SrcReg, SrcSubReg) = (Src1, src1SubIdx).
|
|
/// (DstReg, DstSubReg) = (dst, subIdx1).
|
|
///
|
|
/// The second call returns:
|
|
/// (SrcReg, SrcSubReg) = (Src2, src2SubIdx).
|
|
/// (DstReg, DstSubReg) = (dst, subIdx2).
|
|
///
|
|
/// And so on, until all the sources have been traversed, then
|
|
/// it returns false.
|
|
bool getNextRewritableSource(RegSubRegPair &Src,
|
|
RegSubRegPair &Dst) override {
|
|
// We are looking at v0 = REG_SEQUENCE v1, sub1, v2, sub2, etc.
|
|
|
|
// If this is the first call, move to the first argument.
|
|
if (CurrentSrcIdx == 0) {
|
|
CurrentSrcIdx = 1;
|
|
} else {
|
|
// Otherwise, move to the next argument and check that it is valid.
|
|
CurrentSrcIdx += 2;
|
|
if (CurrentSrcIdx >= CopyLike.getNumOperands())
|
|
return false;
|
|
}
|
|
const MachineOperand &MOInsertedReg = CopyLike.getOperand(CurrentSrcIdx);
|
|
Src.Reg = MOInsertedReg.getReg();
|
|
// If we have to compose sub-register indices, bail out.
|
|
if ((Src.SubReg = MOInsertedReg.getSubReg()))
|
|
return false;
|
|
|
|
// We want to track something that is compatible with the related
|
|
// partial definition.
|
|
Dst.SubReg = CopyLike.getOperand(CurrentSrcIdx + 1).getImm();
|
|
|
|
const MachineOperand &MODef = CopyLike.getOperand(0);
|
|
Dst.Reg = MODef.getReg();
|
|
// If we have to compose sub-registers, bail.
|
|
return MODef.getSubReg() == 0;
|
|
}
|
|
|
|
bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
|
|
// We cannot rewrite out of bound operands.
|
|
// Moreover, rewritable sources are at odd positions.
|
|
if ((CurrentSrcIdx & 1) != 1 || CurrentSrcIdx > CopyLike.getNumOperands())
|
|
return false;
|
|
|
|
MachineOperand &MO = CopyLike.getOperand(CurrentSrcIdx);
|
|
MO.setReg(NewReg);
|
|
MO.setSubReg(NewSubReg);
|
|
return true;
|
|
}
|
|
};
|
|
|
|
} // end anonymous namespace
|
|
|
|
/// Get the appropriated Rewriter for \p MI.
|
|
/// \return A pointer to a dynamically allocated Rewriter or nullptr if no
|
|
/// rewriter works for \p MI.
|
|
static Rewriter *getCopyRewriter(MachineInstr &MI, const TargetInstrInfo &TII) {
|
|
// Handle uncoalescable copy-like instructions.
|
|
if (MI.isBitcast() || MI.isRegSequenceLike() || MI.isInsertSubregLike() ||
|
|
MI.isExtractSubregLike())
|
|
return new UncoalescableRewriter(MI);
|
|
|
|
switch (MI.getOpcode()) {
|
|
default:
|
|
return nullptr;
|
|
case TargetOpcode::COPY:
|
|
return new CopyRewriter(MI);
|
|
case TargetOpcode::INSERT_SUBREG:
|
|
return new InsertSubregRewriter(MI);
|
|
case TargetOpcode::EXTRACT_SUBREG:
|
|
return new ExtractSubregRewriter(MI, TII);
|
|
case TargetOpcode::REG_SEQUENCE:
|
|
return new RegSequenceRewriter(MI);
|
|
}
|
|
}
|
|
|
|
/// \brief Given a \p Def.Reg and Def.SubReg pair, use \p RewriteMap to find
|
|
/// the new source to use for rewrite. If \p HandleMultipleSources is true and
|
|
/// multiple sources for a given \p Def are found along the way, we found a
|
|
/// PHI instructions that needs to be rewritten.
|
|
/// TODO: HandleMultipleSources should be removed once we test PHI handling
|
|
/// with coalescable copies.
|
|
static RegSubRegPair
|
|
getNewSource(MachineRegisterInfo *MRI, const TargetInstrInfo *TII,
|
|
RegSubRegPair Def,
|
|
const PeepholeOptimizer::RewriteMapTy &RewriteMap,
|
|
bool HandleMultipleSources = true) {
|
|
RegSubRegPair LookupSrc(Def.Reg, Def.SubReg);
|
|
while (true) {
|
|
ValueTrackerResult Res = RewriteMap.lookup(LookupSrc);
|
|
// If there are no entries on the map, LookupSrc is the new source.
|
|
if (!Res.isValid())
|
|
return LookupSrc;
|
|
|
|
// There's only one source for this definition, keep searching...
|
|
unsigned NumSrcs = Res.getNumSources();
|
|
if (NumSrcs == 1) {
|
|
LookupSrc.Reg = Res.getSrcReg(0);
|
|
LookupSrc.SubReg = Res.getSrcSubReg(0);
|
|
continue;
|
|
}
|
|
|
|
// TODO: Remove once multiple srcs w/ coalescable copies are supported.
|
|
if (!HandleMultipleSources)
|
|
break;
|
|
|
|
// Multiple sources, recurse into each source to find a new source
|
|
// for it. Then, rewrite the PHI accordingly to its new edges.
|
|
SmallVector<RegSubRegPair, 4> NewPHISrcs;
|
|
for (unsigned i = 0; i < NumSrcs; ++i) {
|
|
RegSubRegPair PHISrc(Res.getSrcReg(i), Res.getSrcSubReg(i));
|
|
NewPHISrcs.push_back(
|
|
getNewSource(MRI, TII, PHISrc, RewriteMap, HandleMultipleSources));
|
|
}
|
|
|
|
// Build the new PHI node and return its def register as the new source.
|
|
MachineInstr &OrigPHI = const_cast<MachineInstr &>(*Res.getInst());
|
|
MachineInstr &NewPHI = insertPHI(*MRI, *TII, NewPHISrcs, OrigPHI);
|
|
DEBUG(dbgs() << "-- getNewSource\n");
|
|
DEBUG(dbgs() << " Replacing: " << OrigPHI);
|
|
DEBUG(dbgs() << " With: " << NewPHI);
|
|
const MachineOperand &MODef = NewPHI.getOperand(0);
|
|
return RegSubRegPair(MODef.getReg(), MODef.getSubReg());
|
|
}
|
|
|
|
return RegSubRegPair(0, 0);
|
|
}
|
|
|
|
/// Optimize generic copy instructions to avoid cross register bank copy.
|
|
/// The optimization looks through a chain of copies and tries to find a source
|
|
/// that has a compatible register class.
|
|
/// Two register classes are considered to be compatible if they share the same
|
|
/// register bank.
|
|
/// New copies issued by this optimization are register allocator
|
|
/// friendly. This optimization does not remove any copy as it may
|
|
/// overconstrain the register allocator, but replaces some operands
|
|
/// when possible.
|
|
/// \pre isCoalescableCopy(*MI) is true.
|
|
/// \return True, when \p MI has been rewritten. False otherwise.
|
|
bool PeepholeOptimizer::optimizeCoalescableCopy(MachineInstr &MI) {
|
|
assert(isCoalescableCopy(MI) && "Invalid argument");
|
|
assert(MI.getDesc().getNumDefs() == 1 &&
|
|
"Coalescer can understand multiple defs?!");
|
|
const MachineOperand &MODef = MI.getOperand(0);
|
|
// Do not rewrite physical definitions.
|
|
if (TargetRegisterInfo::isPhysicalRegister(MODef.getReg()))
|
|
return false;
|
|
|
|
bool Changed = false;
|
|
// Get the right rewriter for the current copy.
|
|
std::unique_ptr<Rewriter> CpyRewriter(getCopyRewriter(MI, *TII));
|
|
// If none exists, bail out.
|
|
if (!CpyRewriter)
|
|
return false;
|
|
// Rewrite each rewritable source.
|
|
RegSubRegPair Src;
|
|
RegSubRegPair TrackPair;
|
|
while (CpyRewriter->getNextRewritableSource(Src, TrackPair)) {
|
|
// Keep track of PHI nodes and its incoming edges when looking for sources.
|
|
RewriteMapTy RewriteMap;
|
|
// Try to find a more suitable source. If we failed to do so, or get the
|
|
// actual source, move to the next source.
|
|
if (!findNextSource(TrackPair, RewriteMap))
|
|
continue;
|
|
|
|
// Get the new source to rewrite. TODO: Only enable handling of multiple
|
|
// sources (PHIs) once we have a motivating example and testcases for it.
|
|
RegSubRegPair NewSrc = getNewSource(MRI, TII, TrackPair, RewriteMap,
|
|
/*HandleMultipleSources=*/false);
|
|
if (Src.Reg == NewSrc.Reg || NewSrc.Reg == 0)
|
|
continue;
|
|
|
|
// Rewrite source.
|
|
if (CpyRewriter->RewriteCurrentSource(NewSrc.Reg, NewSrc.SubReg)) {
|
|
// We may have extended the live-range of NewSrc, account for that.
|
|
MRI->clearKillFlags(NewSrc.Reg);
|
|
Changed = true;
|
|
}
|
|
}
|
|
// TODO: We could have a clean-up method to tidy the instruction.
|
|
// E.g., v0 = INSERT_SUBREG v1, v1.sub0, sub0
|
|
// => v0 = COPY v1
|
|
// Currently we haven't seen motivating example for that and we
|
|
// want to avoid untested code.
|
|
NumRewrittenCopies += Changed;
|
|
return Changed;
|
|
}
|
|
|
|
/// \brief Rewrite the source found through \p Def, by using the \p RewriteMap
|
|
/// and create a new COPY instruction. More info about RewriteMap in
|
|
/// PeepholeOptimizer::findNextSource. Right now this is only used to handle
|
|
/// Uncoalescable copies, since they are copy like instructions that aren't
|
|
/// recognized by the register allocator.
|
|
MachineInstr &
|
|
PeepholeOptimizer::rewriteSource(MachineInstr &CopyLike,
|
|
RegSubRegPair Def, RewriteMapTy &RewriteMap) {
|
|
assert(!TargetRegisterInfo::isPhysicalRegister(Def.Reg) &&
|
|
"We do not rewrite physical registers");
|
|
|
|
// Find the new source to use in the COPY rewrite.
|
|
RegSubRegPair NewSrc = getNewSource(MRI, TII, Def, RewriteMap);
|
|
|
|
// Insert the COPY.
|
|
const TargetRegisterClass *DefRC = MRI->getRegClass(Def.Reg);
|
|
unsigned NewVReg = MRI->createVirtualRegister(DefRC);
|
|
|
|
MachineInstr *NewCopy =
|
|
BuildMI(*CopyLike.getParent(), &CopyLike, CopyLike.getDebugLoc(),
|
|
TII->get(TargetOpcode::COPY), NewVReg)
|
|
.addReg(NewSrc.Reg, 0, NewSrc.SubReg);
|
|
|
|
if (Def.SubReg) {
|
|
NewCopy->getOperand(0).setSubReg(Def.SubReg);
|
|
NewCopy->getOperand(0).setIsUndef();
|
|
}
|
|
|
|
DEBUG(dbgs() << "-- RewriteSource\n");
|
|
DEBUG(dbgs() << " Replacing: " << CopyLike);
|
|
DEBUG(dbgs() << " With: " << *NewCopy);
|
|
MRI->replaceRegWith(Def.Reg, NewVReg);
|
|
MRI->clearKillFlags(NewVReg);
|
|
|
|
// We extended the lifetime of NewSrc.Reg, clear the kill flags to
|
|
// account for that.
|
|
MRI->clearKillFlags(NewSrc.Reg);
|
|
|
|
return *NewCopy;
|
|
}
|
|
|
|
/// \brief Optimize copy-like instructions to create
|
|
/// register coalescer friendly instruction.
|
|
/// The optimization tries to kill-off the \p MI by looking
|
|
/// through a chain of copies to find a source that has a compatible
|
|
/// register class.
|
|
/// If such a source is found, it replace \p MI by a generic COPY
|
|
/// operation.
|
|
/// \pre isUncoalescableCopy(*MI) is true.
|
|
/// \return True, when \p MI has been optimized. In that case, \p MI has
|
|
/// been removed from its parent.
|
|
/// All COPY instructions created, are inserted in \p LocalMIs.
|
|
bool PeepholeOptimizer::optimizeUncoalescableCopy(
|
|
MachineInstr &MI, SmallPtrSetImpl<MachineInstr *> &LocalMIs) {
|
|
assert(isUncoalescableCopy(MI) && "Invalid argument");
|
|
UncoalescableRewriter CpyRewriter(MI);
|
|
|
|
// Rewrite each rewritable source by generating new COPYs. This works
|
|
// differently from optimizeCoalescableCopy since it first makes sure that all
|
|
// definitions can be rewritten.
|
|
RewriteMapTy RewriteMap;
|
|
RegSubRegPair Src;
|
|
RegSubRegPair Def;
|
|
SmallVector<RegSubRegPair, 4> RewritePairs;
|
|
while (CpyRewriter.getNextRewritableSource(Src, Def)) {
|
|
// If a physical register is here, this is probably for a good reason.
|
|
// Do not rewrite that.
|
|
if (TargetRegisterInfo::isPhysicalRegister(Def.Reg))
|
|
return false;
|
|
|
|
// If we do not know how to rewrite this definition, there is no point
|
|
// in trying to kill this instruction.
|
|
if (!findNextSource(Def, RewriteMap))
|
|
return false;
|
|
|
|
RewritePairs.push_back(Def);
|
|
}
|
|
|
|
// The change is possible for all defs, do it.
|
|
for (const RegSubRegPair &Def : RewritePairs) {
|
|
// Rewrite the "copy" in a way the register coalescer understands.
|
|
MachineInstr &NewCopy = rewriteSource(MI, Def, RewriteMap);
|
|
LocalMIs.insert(&NewCopy);
|
|
}
|
|
|
|
// MI is now dead.
|
|
MI.eraseFromParent();
|
|
++NumUncoalescableCopies;
|
|
return true;
|
|
}
|
|
|
|
/// Check whether MI is a candidate for folding into a later instruction.
|
|
/// We only fold loads to virtual registers and the virtual register defined
|
|
/// has a single use.
|
|
bool PeepholeOptimizer::isLoadFoldable(
|
|
MachineInstr &MI, SmallSet<unsigned, 16> &FoldAsLoadDefCandidates) {
|
|
if (!MI.canFoldAsLoad() || !MI.mayLoad())
|
|
return false;
|
|
const MCInstrDesc &MCID = MI.getDesc();
|
|
if (MCID.getNumDefs() != 1)
|
|
return false;
|
|
|
|
unsigned Reg = MI.getOperand(0).getReg();
|
|
// To reduce compilation time, we check MRI->hasOneNonDBGUse when inserting
|
|
// loads. It should be checked when processing uses of the load, since
|
|
// uses can be removed during peephole.
|
|
if (!MI.getOperand(0).getSubReg() &&
|
|
TargetRegisterInfo::isVirtualRegister(Reg) &&
|
|
MRI->hasOneNonDBGUse(Reg)) {
|
|
FoldAsLoadDefCandidates.insert(Reg);
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
bool PeepholeOptimizer::isMoveImmediate(
|
|
MachineInstr &MI, SmallSet<unsigned, 4> &ImmDefRegs,
|
|
DenseMap<unsigned, MachineInstr *> &ImmDefMIs) {
|
|
const MCInstrDesc &MCID = MI.getDesc();
|
|
if (!MI.isMoveImmediate())
|
|
return false;
|
|
if (MCID.getNumDefs() != 1)
|
|
return false;
|
|
unsigned Reg = MI.getOperand(0).getReg();
|
|
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
|
|
ImmDefMIs.insert(std::make_pair(Reg, &MI));
|
|
ImmDefRegs.insert(Reg);
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Try folding register operands that are defined by move immediate
|
|
/// instructions, i.e. a trivial constant folding optimization, if
|
|
/// and only if the def and use are in the same BB.
|
|
bool PeepholeOptimizer::foldImmediate(MachineInstr &MI,
|
|
SmallSet<unsigned, 4> &ImmDefRegs,
|
|
DenseMap<unsigned, MachineInstr *> &ImmDefMIs) {
|
|
for (unsigned i = 0, e = MI.getDesc().getNumOperands(); i != e; ++i) {
|
|
MachineOperand &MO = MI.getOperand(i);
|
|
if (!MO.isReg() || MO.isDef())
|
|
continue;
|
|
// Ignore dead implicit defs.
|
|
if (MO.isImplicit() && MO.isDead())
|
|
continue;
|
|
unsigned Reg = MO.getReg();
|
|
if (!TargetRegisterInfo::isVirtualRegister(Reg))
|
|
continue;
|
|
if (ImmDefRegs.count(Reg) == 0)
|
|
continue;
|
|
DenseMap<unsigned, MachineInstr*>::iterator II = ImmDefMIs.find(Reg);
|
|
assert(II != ImmDefMIs.end() && "couldn't find immediate definition");
|
|
if (TII->FoldImmediate(MI, *II->second, Reg, MRI)) {
|
|
++NumImmFold;
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// FIXME: This is very simple and misses some cases which should be handled when
|
|
// motivating examples are found.
|
|
//
|
|
// The copy rewriting logic should look at uses as well as defs and be able to
|
|
// eliminate copies across blocks.
|
|
//
|
|
// Later copies that are subregister extracts will also not be eliminated since
|
|
// only the first copy is considered.
|
|
//
|
|
// e.g.
|
|
// %1 = COPY %0
|
|
// %2 = COPY %0:sub1
|
|
//
|
|
// Should replace %2 uses with %1:sub1
|
|
bool PeepholeOptimizer::foldRedundantCopy(MachineInstr &MI,
|
|
SmallSet<unsigned, 4> &CopySrcRegs,
|
|
DenseMap<unsigned, MachineInstr *> &CopyMIs) {
|
|
assert(MI.isCopy() && "expected a COPY machine instruction");
|
|
|
|
unsigned SrcReg = MI.getOperand(1).getReg();
|
|
if (!TargetRegisterInfo::isVirtualRegister(SrcReg))
|
|
return false;
|
|
|
|
unsigned DstReg = MI.getOperand(0).getReg();
|
|
if (!TargetRegisterInfo::isVirtualRegister(DstReg))
|
|
return false;
|
|
|
|
if (CopySrcRegs.insert(SrcReg).second) {
|
|
// First copy of this reg seen.
|
|
CopyMIs.insert(std::make_pair(SrcReg, &MI));
|
|
return false;
|
|
}
|
|
|
|
MachineInstr *PrevCopy = CopyMIs.find(SrcReg)->second;
|
|
|
|
unsigned SrcSubReg = MI.getOperand(1).getSubReg();
|
|
unsigned PrevSrcSubReg = PrevCopy->getOperand(1).getSubReg();
|
|
|
|
// Can't replace different subregister extracts.
|
|
if (SrcSubReg != PrevSrcSubReg)
|
|
return false;
|
|
|
|
unsigned PrevDstReg = PrevCopy->getOperand(0).getReg();
|
|
|
|
// Only replace if the copy register class is the same.
|
|
//
|
|
// TODO: If we have multiple copies to different register classes, we may want
|
|
// to track multiple copies of the same source register.
|
|
if (MRI->getRegClass(DstReg) != MRI->getRegClass(PrevDstReg))
|
|
return false;
|
|
|
|
MRI->replaceRegWith(DstReg, PrevDstReg);
|
|
|
|
// Lifetime of the previous copy has been extended.
|
|
MRI->clearKillFlags(PrevDstReg);
|
|
return true;
|
|
}
|
|
|
|
bool PeepholeOptimizer::isNAPhysCopy(unsigned Reg) {
|
|
return TargetRegisterInfo::isPhysicalRegister(Reg) &&
|
|
!MRI->isAllocatable(Reg);
|
|
}
|
|
|
|
bool PeepholeOptimizer::foldRedundantNAPhysCopy(
|
|
MachineInstr &MI, DenseMap<unsigned, MachineInstr *> &NAPhysToVirtMIs) {
|
|
assert(MI.isCopy() && "expected a COPY machine instruction");
|
|
|
|
if (DisableNAPhysCopyOpt)
|
|
return false;
|
|
|
|
unsigned DstReg = MI.getOperand(0).getReg();
|
|
unsigned SrcReg = MI.getOperand(1).getReg();
|
|
if (isNAPhysCopy(SrcReg) && TargetRegisterInfo::isVirtualRegister(DstReg)) {
|
|
// %vreg = COPY %physreg
|
|
// Avoid using a datastructure which can track multiple live non-allocatable
|
|
// phys->virt copies since LLVM doesn't seem to do this.
|
|
NAPhysToVirtMIs.insert({SrcReg, &MI});
|
|
return false;
|
|
}
|
|
|
|
if (!(TargetRegisterInfo::isVirtualRegister(SrcReg) && isNAPhysCopy(DstReg)))
|
|
return false;
|
|
|
|
// %physreg = COPY %vreg
|
|
auto PrevCopy = NAPhysToVirtMIs.find(DstReg);
|
|
if (PrevCopy == NAPhysToVirtMIs.end()) {
|
|
// We can't remove the copy: there was an intervening clobber of the
|
|
// non-allocatable physical register after the copy to virtual.
|
|
DEBUG(dbgs() << "NAPhysCopy: intervening clobber forbids erasing " << MI);
|
|
return false;
|
|
}
|
|
|
|
unsigned PrevDstReg = PrevCopy->second->getOperand(0).getReg();
|
|
if (PrevDstReg == SrcReg) {
|
|
// Remove the virt->phys copy: we saw the virtual register definition, and
|
|
// the non-allocatable physical register's state hasn't changed since then.
|
|
DEBUG(dbgs() << "NAPhysCopy: erasing " << MI);
|
|
++NumNAPhysCopies;
|
|
return true;
|
|
}
|
|
|
|
// Potential missed optimization opportunity: we saw a different virtual
|
|
// register get a copy of the non-allocatable physical register, and we only
|
|
// track one such copy. Avoid getting confused by this new non-allocatable
|
|
// physical register definition, and remove it from the tracked copies.
|
|
DEBUG(dbgs() << "NAPhysCopy: missed opportunity " << MI);
|
|
NAPhysToVirtMIs.erase(PrevCopy);
|
|
return false;
|
|
}
|
|
|
|
/// \bried Returns true if \p MO is a virtual register operand.
|
|
static bool isVirtualRegisterOperand(MachineOperand &MO) {
|
|
if (!MO.isReg())
|
|
return false;
|
|
return TargetRegisterInfo::isVirtualRegister(MO.getReg());
|
|
}
|
|
|
|
bool PeepholeOptimizer::findTargetRecurrence(
|
|
unsigned Reg, const SmallSet<unsigned, 2> &TargetRegs,
|
|
RecurrenceCycle &RC) {
|
|
// Recurrence found if Reg is in TargetRegs.
|
|
if (TargetRegs.count(Reg))
|
|
return true;
|
|
|
|
// TODO: Curerntly, we only allow the last instruction of the recurrence
|
|
// cycle (the instruction that feeds the PHI instruction) to have more than
|
|
// one uses to guarantee that commuting operands does not tie registers
|
|
// with overlapping live range. Once we have actual live range info of
|
|
// each register, this constraint can be relaxed.
|
|
if (!MRI->hasOneNonDBGUse(Reg))
|
|
return false;
|
|
|
|
// Give up if the reccurrence chain length is longer than the limit.
|
|
if (RC.size() >= MaxRecurrenceChain)
|
|
return false;
|
|
|
|
MachineInstr &MI = *(MRI->use_instr_nodbg_begin(Reg));
|
|
unsigned Idx = MI.findRegisterUseOperandIdx(Reg);
|
|
|
|
// Only interested in recurrences whose instructions have only one def, which
|
|
// is a virtual register.
|
|
if (MI.getDesc().getNumDefs() != 1)
|
|
return false;
|
|
|
|
MachineOperand &DefOp = MI.getOperand(0);
|
|
if (!isVirtualRegisterOperand(DefOp))
|
|
return false;
|
|
|
|
// Check if def operand of MI is tied to any use operand. We are only
|
|
// interested in the case that all the instructions in the recurrence chain
|
|
// have there def operand tied with one of the use operand.
|
|
unsigned TiedUseIdx;
|
|
if (!MI.isRegTiedToUseOperand(0, &TiedUseIdx))
|
|
return false;
|
|
|
|
if (Idx == TiedUseIdx) {
|
|
RC.push_back(RecurrenceInstr(&MI));
|
|
return findTargetRecurrence(DefOp.getReg(), TargetRegs, RC);
|
|
} else {
|
|
// If Idx is not TiedUseIdx, check if Idx is commutable with TiedUseIdx.
|
|
unsigned CommIdx = TargetInstrInfo::CommuteAnyOperandIndex;
|
|
if (TII->findCommutedOpIndices(MI, Idx, CommIdx) && CommIdx == TiedUseIdx) {
|
|
RC.push_back(RecurrenceInstr(&MI, Idx, CommIdx));
|
|
return findTargetRecurrence(DefOp.getReg(), TargetRegs, RC);
|
|
}
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Phi instructions will eventually be lowered to copy instructions.
|
|
/// If phi is in a loop header, a recurrence may formulated around the source
|
|
/// and destination of the phi. For such case commuting operands of the
|
|
/// instructions in the recurrence may enable coalescing of the copy instruction
|
|
/// generated from the phi. For example, if there is a recurrence of
|
|
///
|
|
/// LoopHeader:
|
|
/// %1 = phi(%0, %100)
|
|
/// LoopLatch:
|
|
/// %0<def, tied1> = ADD %2<def, tied0>, %1
|
|
///
|
|
/// , the fact that %0 and %2 are in the same tied operands set makes
|
|
/// the coalescing of copy instruction generated from the phi in
|
|
/// LoopHeader(i.e. %1 = COPY %0) impossible, because %1 and
|
|
/// %2 have overlapping live range. This introduces additional move
|
|
/// instruction to the final assembly. However, if we commute %2 and
|
|
/// %1 of ADD instruction, the redundant move instruction can be
|
|
/// avoided.
|
|
bool PeepholeOptimizer::optimizeRecurrence(MachineInstr &PHI) {
|
|
SmallSet<unsigned, 2> TargetRegs;
|
|
for (unsigned Idx = 1; Idx < PHI.getNumOperands(); Idx += 2) {
|
|
MachineOperand &MO = PHI.getOperand(Idx);
|
|
assert(isVirtualRegisterOperand(MO) && "Invalid PHI instruction");
|
|
TargetRegs.insert(MO.getReg());
|
|
}
|
|
|
|
bool Changed = false;
|
|
RecurrenceCycle RC;
|
|
if (findTargetRecurrence(PHI.getOperand(0).getReg(), TargetRegs, RC)) {
|
|
// Commutes operands of instructions in RC if necessary so that the copy to
|
|
// be generated from PHI can be coalesced.
|
|
DEBUG(dbgs() << "Optimize recurrence chain from " << PHI);
|
|
for (auto &RI : RC) {
|
|
DEBUG(dbgs() << "\tInst: " << *(RI.getMI()));
|
|
auto CP = RI.getCommutePair();
|
|
if (CP) {
|
|
Changed = true;
|
|
TII->commuteInstruction(*(RI.getMI()), false, (*CP).first,
|
|
(*CP).second);
|
|
DEBUG(dbgs() << "\t\tCommuted: " << *(RI.getMI()));
|
|
}
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
|
|
if (skipFunction(MF.getFunction()))
|
|
return false;
|
|
|
|
DEBUG(dbgs() << "********** PEEPHOLE OPTIMIZER **********\n");
|
|
DEBUG(dbgs() << "********** Function: " << MF.getName() << '\n');
|
|
|
|
if (DisablePeephole)
|
|
return false;
|
|
|
|
TII = MF.getSubtarget().getInstrInfo();
|
|
TRI = MF.getSubtarget().getRegisterInfo();
|
|
MRI = &MF.getRegInfo();
|
|
DT = Aggressive ? &getAnalysis<MachineDominatorTree>() : nullptr;
|
|
MLI = &getAnalysis<MachineLoopInfo>();
|
|
|
|
bool Changed = false;
|
|
|
|
for (MachineBasicBlock &MBB : MF) {
|
|
bool SeenMoveImm = false;
|
|
|
|
// During this forward scan, at some point it needs to answer the question
|
|
// "given a pointer to an MI in the current BB, is it located before or
|
|
// after the current instruction".
|
|
// To perform this, the following set keeps track of the MIs already seen
|
|
// during the scan, if a MI is not in the set, it is assumed to be located
|
|
// after. Newly created MIs have to be inserted in the set as well.
|
|
SmallPtrSet<MachineInstr*, 16> LocalMIs;
|
|
SmallSet<unsigned, 4> ImmDefRegs;
|
|
DenseMap<unsigned, MachineInstr*> ImmDefMIs;
|
|
SmallSet<unsigned, 16> FoldAsLoadDefCandidates;
|
|
|
|
// Track when a non-allocatable physical register is copied to a virtual
|
|
// register so that useless moves can be removed.
|
|
//
|
|
// %physreg is the map index; MI is the last valid `%vreg = COPY %physreg`
|
|
// without any intervening re-definition of %physreg.
|
|
DenseMap<unsigned, MachineInstr *> NAPhysToVirtMIs;
|
|
|
|
// Set of virtual registers that are copied from.
|
|
SmallSet<unsigned, 4> CopySrcRegs;
|
|
DenseMap<unsigned, MachineInstr *> CopySrcMIs;
|
|
|
|
bool IsLoopHeader = MLI->isLoopHeader(&MBB);
|
|
|
|
for (MachineBasicBlock::iterator MII = MBB.begin(), MIE = MBB.end();
|
|
MII != MIE; ) {
|
|
MachineInstr *MI = &*MII;
|
|
// We may be erasing MI below, increment MII now.
|
|
++MII;
|
|
LocalMIs.insert(MI);
|
|
|
|
// Skip debug values. They should not affect this peephole optimization.
|
|
if (MI->isDebugValue())
|
|
continue;
|
|
|
|
if (MI->isPosition())
|
|
continue;
|
|
|
|
if (IsLoopHeader && MI->isPHI()) {
|
|
if (optimizeRecurrence(*MI)) {
|
|
Changed = true;
|
|
continue;
|
|
}
|
|
}
|
|
|
|
if (!MI->isCopy()) {
|
|
for (const MachineOperand &MO : MI->operands()) {
|
|
// Visit all operands: definitions can be implicit or explicit.
|
|
if (MO.isReg()) {
|
|
unsigned Reg = MO.getReg();
|
|
if (MO.isDef() && isNAPhysCopy(Reg)) {
|
|
const auto &Def = NAPhysToVirtMIs.find(Reg);
|
|
if (Def != NAPhysToVirtMIs.end()) {
|
|
// A new definition of the non-allocatable physical register
|
|
// invalidates previous copies.
|
|
DEBUG(dbgs() << "NAPhysCopy: invalidating because of " << *MI);
|
|
NAPhysToVirtMIs.erase(Def);
|
|
}
|
|
}
|
|
} else if (MO.isRegMask()) {
|
|
const uint32_t *RegMask = MO.getRegMask();
|
|
for (auto &RegMI : NAPhysToVirtMIs) {
|
|
unsigned Def = RegMI.first;
|
|
if (MachineOperand::clobbersPhysReg(RegMask, Def)) {
|
|
DEBUG(dbgs() << "NAPhysCopy: invalidating because of " << *MI);
|
|
NAPhysToVirtMIs.erase(Def);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
if (MI->isImplicitDef() || MI->isKill())
|
|
continue;
|
|
|
|
if (MI->isInlineAsm() || MI->hasUnmodeledSideEffects()) {
|
|
// Blow away all non-allocatable physical registers knowledge since we
|
|
// don't know what's correct anymore.
|
|
//
|
|
// FIXME: handle explicit asm clobbers.
|
|
DEBUG(dbgs() << "NAPhysCopy: blowing away all info due to " << *MI);
|
|
NAPhysToVirtMIs.clear();
|
|
}
|
|
|
|
if ((isUncoalescableCopy(*MI) &&
|
|
optimizeUncoalescableCopy(*MI, LocalMIs)) ||
|
|
(MI->isCompare() && optimizeCmpInstr(*MI)) ||
|
|
(MI->isSelect() && optimizeSelect(*MI, LocalMIs))) {
|
|
// MI is deleted.
|
|
LocalMIs.erase(MI);
|
|
Changed = true;
|
|
continue;
|
|
}
|
|
|
|
if (MI->isConditionalBranch() && optimizeCondBranch(*MI)) {
|
|
Changed = true;
|
|
continue;
|
|
}
|
|
|
|
if (isCoalescableCopy(*MI) && optimizeCoalescableCopy(*MI)) {
|
|
// MI is just rewritten.
|
|
Changed = true;
|
|
continue;
|
|
}
|
|
|
|
if (MI->isCopy() &&
|
|
(foldRedundantCopy(*MI, CopySrcRegs, CopySrcMIs) ||
|
|
foldRedundantNAPhysCopy(*MI, NAPhysToVirtMIs))) {
|
|
LocalMIs.erase(MI);
|
|
MI->eraseFromParent();
|
|
Changed = true;
|
|
continue;
|
|
}
|
|
|
|
if (isMoveImmediate(*MI, ImmDefRegs, ImmDefMIs)) {
|
|
SeenMoveImm = true;
|
|
} else {
|
|
Changed |= optimizeExtInstr(*MI, MBB, LocalMIs);
|
|
// optimizeExtInstr might have created new instructions after MI
|
|
// and before the already incremented MII. Adjust MII so that the
|
|
// next iteration sees the new instructions.
|
|
MII = MI;
|
|
++MII;
|
|
if (SeenMoveImm)
|
|
Changed |= foldImmediate(*MI, ImmDefRegs, ImmDefMIs);
|
|
}
|
|
|
|
// Check whether MI is a load candidate for folding into a later
|
|
// instruction. If MI is not a candidate, check whether we can fold an
|
|
// earlier load into MI.
|
|
if (!isLoadFoldable(*MI, FoldAsLoadDefCandidates) &&
|
|
!FoldAsLoadDefCandidates.empty()) {
|
|
|
|
// We visit each operand even after successfully folding a previous
|
|
// one. This allows us to fold multiple loads into a single
|
|
// instruction. We do assume that optimizeLoadInstr doesn't insert
|
|
// foldable uses earlier in the argument list. Since we don't restart
|
|
// iteration, we'd miss such cases.
|
|
const MCInstrDesc &MIDesc = MI->getDesc();
|
|
for (unsigned i = MIDesc.getNumDefs(); i != MI->getNumOperands();
|
|
++i) {
|
|
const MachineOperand &MOp = MI->getOperand(i);
|
|
if (!MOp.isReg())
|
|
continue;
|
|
unsigned FoldAsLoadDefReg = MOp.getReg();
|
|
if (FoldAsLoadDefCandidates.count(FoldAsLoadDefReg)) {
|
|
// We need to fold load after optimizeCmpInstr, since
|
|
// optimizeCmpInstr can enable folding by converting SUB to CMP.
|
|
// Save FoldAsLoadDefReg because optimizeLoadInstr() resets it and
|
|
// we need it for markUsesInDebugValueAsUndef().
|
|
unsigned FoldedReg = FoldAsLoadDefReg;
|
|
MachineInstr *DefMI = nullptr;
|
|
if (MachineInstr *FoldMI =
|
|
TII->optimizeLoadInstr(*MI, MRI, FoldAsLoadDefReg, DefMI)) {
|
|
// Update LocalMIs since we replaced MI with FoldMI and deleted
|
|
// DefMI.
|
|
DEBUG(dbgs() << "Replacing: " << *MI);
|
|
DEBUG(dbgs() << " With: " << *FoldMI);
|
|
LocalMIs.erase(MI);
|
|
LocalMIs.erase(DefMI);
|
|
LocalMIs.insert(FoldMI);
|
|
MI->eraseFromParent();
|
|
DefMI->eraseFromParent();
|
|
MRI->markUsesInDebugValueAsUndef(FoldedReg);
|
|
FoldAsLoadDefCandidates.erase(FoldedReg);
|
|
++NumLoadFold;
|
|
|
|
// MI is replaced with FoldMI so we can continue trying to fold
|
|
Changed = true;
|
|
MI = FoldMI;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// If we run into an instruction we can't fold across, discard
|
|
// the load candidates. Note: We might be able to fold *into* this
|
|
// instruction, so this needs to be after the folding logic.
|
|
if (MI->isLoadFoldBarrier()) {
|
|
DEBUG(dbgs() << "Encountered load fold barrier on " << *MI);
|
|
FoldAsLoadDefCandidates.clear();
|
|
}
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
ValueTrackerResult ValueTracker::getNextSourceFromCopy() {
|
|
assert(Def->isCopy() && "Invalid definition");
|
|
// Copy instruction are supposed to be: Def = Src.
|
|
// If someone breaks this assumption, bad things will happen everywhere.
|
|
assert(Def->getNumOperands() == 2 && "Invalid number of operands");
|
|
|
|
if (Def->getOperand(DefIdx).getSubReg() != DefSubReg)
|
|
// If we look for a different subreg, it means we want a subreg of src.
|
|
// Bails as we do not support composing subregs yet.
|
|
return ValueTrackerResult();
|
|
// Otherwise, we want the whole source.
|
|
const MachineOperand &Src = Def->getOperand(1);
|
|
if (Src.isUndef())
|
|
return ValueTrackerResult();
|
|
return ValueTrackerResult(Src.getReg(), Src.getSubReg());
|
|
}
|
|
|
|
ValueTrackerResult ValueTracker::getNextSourceFromBitcast() {
|
|
assert(Def->isBitcast() && "Invalid definition");
|
|
|
|
// Bail if there are effects that a plain copy will not expose.
|
|
if (Def->hasUnmodeledSideEffects())
|
|
return ValueTrackerResult();
|
|
|
|
// Bitcasts with more than one def are not supported.
|
|
if (Def->getDesc().getNumDefs() != 1)
|
|
return ValueTrackerResult();
|
|
const MachineOperand DefOp = Def->getOperand(DefIdx);
|
|
if (DefOp.getSubReg() != DefSubReg)
|
|
// If we look for a different subreg, it means we want a subreg of the src.
|
|
// Bails as we do not support composing subregs yet.
|
|
return ValueTrackerResult();
|
|
|
|
unsigned SrcIdx = Def->getNumOperands();
|
|
for (unsigned OpIdx = DefIdx + 1, EndOpIdx = SrcIdx; OpIdx != EndOpIdx;
|
|
++OpIdx) {
|
|
const MachineOperand &MO = Def->getOperand(OpIdx);
|
|
if (!MO.isReg() || !MO.getReg())
|
|
continue;
|
|
// Ignore dead implicit defs.
|
|
if (MO.isImplicit() && MO.isDead())
|
|
continue;
|
|
assert(!MO.isDef() && "We should have skipped all the definitions by now");
|
|
if (SrcIdx != EndOpIdx)
|
|
// Multiple sources?
|
|
return ValueTrackerResult();
|
|
SrcIdx = OpIdx;
|
|
}
|
|
|
|
// Stop when any user of the bitcast is a SUBREG_TO_REG, replacing with a COPY
|
|
// will break the assumed guarantees for the upper bits.
|
|
for (const MachineInstr &UseMI : MRI.use_nodbg_instructions(DefOp.getReg())) {
|
|
if (UseMI.isSubregToReg())
|
|
return ValueTrackerResult();
|
|
}
|
|
|
|
const MachineOperand &Src = Def->getOperand(SrcIdx);
|
|
if (Src.isUndef())
|
|
return ValueTrackerResult();
|
|
return ValueTrackerResult(Src.getReg(), Src.getSubReg());
|
|
}
|
|
|
|
ValueTrackerResult ValueTracker::getNextSourceFromRegSequence() {
|
|
assert((Def->isRegSequence() || Def->isRegSequenceLike()) &&
|
|
"Invalid definition");
|
|
|
|
if (Def->getOperand(DefIdx).getSubReg())
|
|
// If we are composing subregs, bail out.
|
|
// The case we are checking is Def.<subreg> = REG_SEQUENCE.
|
|
// This should almost never happen as the SSA property is tracked at
|
|
// the register level (as opposed to the subreg level).
|
|
// I.e.,
|
|
// Def.sub0 =
|
|
// Def.sub1 =
|
|
// is a valid SSA representation for Def.sub0 and Def.sub1, but not for
|
|
// Def. Thus, it must not be generated.
|
|
// However, some code could theoretically generates a single
|
|
// Def.sub0 (i.e, not defining the other subregs) and we would
|
|
// have this case.
|
|
// If we can ascertain (or force) that this never happens, we could
|
|
// turn that into an assertion.
|
|
return ValueTrackerResult();
|
|
|
|
if (!TII)
|
|
// We could handle the REG_SEQUENCE here, but we do not want to
|
|
// duplicate the code from the generic TII.
|
|
return ValueTrackerResult();
|
|
|
|
SmallVector<RegSubRegPairAndIdx, 8> RegSeqInputRegs;
|
|
if (!TII->getRegSequenceInputs(*Def, DefIdx, RegSeqInputRegs))
|
|
return ValueTrackerResult();
|
|
|
|
// We are looking at:
|
|
// Def = REG_SEQUENCE v0, sub0, v1, sub1, ...
|
|
// Check if one of the operand defines the subreg we are interested in.
|
|
for (const RegSubRegPairAndIdx &RegSeqInput : RegSeqInputRegs) {
|
|
if (RegSeqInput.SubIdx == DefSubReg) {
|
|
if (RegSeqInput.SubReg)
|
|
// Bail if we have to compose sub registers.
|
|
return ValueTrackerResult();
|
|
|
|
return ValueTrackerResult(RegSeqInput.Reg, RegSeqInput.SubReg);
|
|
}
|
|
}
|
|
|
|
// If the subreg we are tracking is super-defined by another subreg,
|
|
// we could follow this value. However, this would require to compose
|
|
// the subreg and we do not do that for now.
|
|
return ValueTrackerResult();
|
|
}
|
|
|
|
ValueTrackerResult ValueTracker::getNextSourceFromInsertSubreg() {
|
|
assert((Def->isInsertSubreg() || Def->isInsertSubregLike()) &&
|
|
"Invalid definition");
|
|
|
|
if (Def->getOperand(DefIdx).getSubReg())
|
|
// If we are composing subreg, bail out.
|
|
// Same remark as getNextSourceFromRegSequence.
|
|
// I.e., this may be turned into an assert.
|
|
return ValueTrackerResult();
|
|
|
|
if (!TII)
|
|
// We could handle the REG_SEQUENCE here, but we do not want to
|
|
// duplicate the code from the generic TII.
|
|
return ValueTrackerResult();
|
|
|
|
RegSubRegPair BaseReg;
|
|
RegSubRegPairAndIdx InsertedReg;
|
|
if (!TII->getInsertSubregInputs(*Def, DefIdx, BaseReg, InsertedReg))
|
|
return ValueTrackerResult();
|
|
|
|
// We are looking at:
|
|
// Def = INSERT_SUBREG v0, v1, sub1
|
|
// There are two cases:
|
|
// 1. DefSubReg == sub1, get v1.
|
|
// 2. DefSubReg != sub1, the value may be available through v0.
|
|
|
|
// #1 Check if the inserted register matches the required sub index.
|
|
if (InsertedReg.SubIdx == DefSubReg) {
|
|
return ValueTrackerResult(InsertedReg.Reg, InsertedReg.SubReg);
|
|
}
|
|
// #2 Otherwise, if the sub register we are looking for is not partial
|
|
// defined by the inserted element, we can look through the main
|
|
// register (v0).
|
|
const MachineOperand &MODef = Def->getOperand(DefIdx);
|
|
// If the result register (Def) and the base register (v0) do not
|
|
// have the same register class or if we have to compose
|
|
// subregisters, bail out.
|
|
if (MRI.getRegClass(MODef.getReg()) != MRI.getRegClass(BaseReg.Reg) ||
|
|
BaseReg.SubReg)
|
|
return ValueTrackerResult();
|
|
|
|
// Get the TRI and check if the inserted sub-register overlaps with the
|
|
// sub-register we are tracking.
|
|
const TargetRegisterInfo *TRI = MRI.getTargetRegisterInfo();
|
|
if (!TRI ||
|
|
!(TRI->getSubRegIndexLaneMask(DefSubReg) &
|
|
TRI->getSubRegIndexLaneMask(InsertedReg.SubIdx)).none())
|
|
return ValueTrackerResult();
|
|
// At this point, the value is available in v0 via the same subreg
|
|
// we used for Def.
|
|
return ValueTrackerResult(BaseReg.Reg, DefSubReg);
|
|
}
|
|
|
|
ValueTrackerResult ValueTracker::getNextSourceFromExtractSubreg() {
|
|
assert((Def->isExtractSubreg() ||
|
|
Def->isExtractSubregLike()) && "Invalid definition");
|
|
// We are looking at:
|
|
// Def = EXTRACT_SUBREG v0, sub0
|
|
|
|
// Bail if we have to compose sub registers.
|
|
// Indeed, if DefSubReg != 0, we would have to compose it with sub0.
|
|
if (DefSubReg)
|
|
return ValueTrackerResult();
|
|
|
|
if (!TII)
|
|
// We could handle the EXTRACT_SUBREG here, but we do not want to
|
|
// duplicate the code from the generic TII.
|
|
return ValueTrackerResult();
|
|
|
|
RegSubRegPairAndIdx ExtractSubregInputReg;
|
|
if (!TII->getExtractSubregInputs(*Def, DefIdx, ExtractSubregInputReg))
|
|
return ValueTrackerResult();
|
|
|
|
// Bail if we have to compose sub registers.
|
|
// Likewise, if v0.subreg != 0, we would have to compose v0.subreg with sub0.
|
|
if (ExtractSubregInputReg.SubReg)
|
|
return ValueTrackerResult();
|
|
// Otherwise, the value is available in the v0.sub0.
|
|
return ValueTrackerResult(ExtractSubregInputReg.Reg,
|
|
ExtractSubregInputReg.SubIdx);
|
|
}
|
|
|
|
ValueTrackerResult ValueTracker::getNextSourceFromSubregToReg() {
|
|
assert(Def->isSubregToReg() && "Invalid definition");
|
|
// We are looking at:
|
|
// Def = SUBREG_TO_REG Imm, v0, sub0
|
|
|
|
// Bail if we have to compose sub registers.
|
|
// If DefSubReg != sub0, we would have to check that all the bits
|
|
// we track are included in sub0 and if yes, we would have to
|
|
// determine the right subreg in v0.
|
|
if (DefSubReg != Def->getOperand(3).getImm())
|
|
return ValueTrackerResult();
|
|
// Bail if we have to compose sub registers.
|
|
// Likewise, if v0.subreg != 0, we would have to compose it with sub0.
|
|
if (Def->getOperand(2).getSubReg())
|
|
return ValueTrackerResult();
|
|
|
|
return ValueTrackerResult(Def->getOperand(2).getReg(),
|
|
Def->getOperand(3).getImm());
|
|
}
|
|
|
|
/// Explore each PHI incoming operand and return its sources.
|
|
ValueTrackerResult ValueTracker::getNextSourceFromPHI() {
|
|
assert(Def->isPHI() && "Invalid definition");
|
|
ValueTrackerResult Res;
|
|
|
|
// If we look for a different subreg, bail as we do not support composing
|
|
// subregs yet.
|
|
if (Def->getOperand(0).getSubReg() != DefSubReg)
|
|
return ValueTrackerResult();
|
|
|
|
// Return all register sources for PHI instructions.
|
|
for (unsigned i = 1, e = Def->getNumOperands(); i < e; i += 2) {
|
|
const MachineOperand &MO = Def->getOperand(i);
|
|
assert(MO.isReg() && "Invalid PHI instruction");
|
|
// We have no code to deal with undef operands. They shouldn't happen in
|
|
// normal programs anyway.
|
|
if (MO.isUndef())
|
|
return ValueTrackerResult();
|
|
Res.addSource(MO.getReg(), MO.getSubReg());
|
|
}
|
|
|
|
return Res;
|
|
}
|
|
|
|
ValueTrackerResult ValueTracker::getNextSourceImpl() {
|
|
assert(Def && "This method needs a valid definition");
|
|
|
|
assert(((Def->getOperand(DefIdx).isDef() &&
|
|
(DefIdx < Def->getDesc().getNumDefs() ||
|
|
Def->getDesc().isVariadic())) ||
|
|
Def->getOperand(DefIdx).isImplicit()) &&
|
|
"Invalid DefIdx");
|
|
if (Def->isCopy())
|
|
return getNextSourceFromCopy();
|
|
if (Def->isBitcast())
|
|
return getNextSourceFromBitcast();
|
|
// All the remaining cases involve "complex" instructions.
|
|
// Bail if we did not ask for the advanced tracking.
|
|
if (DisableAdvCopyOpt)
|
|
return ValueTrackerResult();
|
|
if (Def->isRegSequence() || Def->isRegSequenceLike())
|
|
return getNextSourceFromRegSequence();
|
|
if (Def->isInsertSubreg() || Def->isInsertSubregLike())
|
|
return getNextSourceFromInsertSubreg();
|
|
if (Def->isExtractSubreg() || Def->isExtractSubregLike())
|
|
return getNextSourceFromExtractSubreg();
|
|
if (Def->isSubregToReg())
|
|
return getNextSourceFromSubregToReg();
|
|
if (Def->isPHI())
|
|
return getNextSourceFromPHI();
|
|
return ValueTrackerResult();
|
|
}
|
|
|
|
ValueTrackerResult ValueTracker::getNextSource() {
|
|
// If we reach a point where we cannot move up in the use-def chain,
|
|
// there is nothing we can get.
|
|
if (!Def)
|
|
return ValueTrackerResult();
|
|
|
|
ValueTrackerResult Res = getNextSourceImpl();
|
|
if (Res.isValid()) {
|
|
// Update definition, definition index, and subregister for the
|
|
// next call of getNextSource.
|
|
// Update the current register.
|
|
bool OneRegSrc = Res.getNumSources() == 1;
|
|
if (OneRegSrc)
|
|
Reg = Res.getSrcReg(0);
|
|
// Update the result before moving up in the use-def chain
|
|
// with the instruction containing the last found sources.
|
|
Res.setInst(Def);
|
|
|
|
// If we can still move up in the use-def chain, move to the next
|
|
// definition.
|
|
if (!TargetRegisterInfo::isPhysicalRegister(Reg) && OneRegSrc) {
|
|
MachineRegisterInfo::def_iterator DI = MRI.def_begin(Reg);
|
|
if (DI != MRI.def_end()) {
|
|
Def = DI->getParent();
|
|
DefIdx = DI.getOperandNo();
|
|
DefSubReg = Res.getSrcSubReg(0);
|
|
} else {
|
|
Def = nullptr;
|
|
}
|
|
return Res;
|
|
}
|
|
}
|
|
// If we end up here, this means we will not be able to find another source
|
|
// for the next iteration. Make sure any new call to getNextSource bails out
|
|
// early by cutting the use-def chain.
|
|
Def = nullptr;
|
|
return Res;
|
|
}
|