llvm-project/llvm/lib/Target/R600/SIShrinkInstructions.cpp

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//===-- SIShrinkInstructions.cpp - Shrink Instructions --------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
/// The pass tries to use the 32-bit encoding for instructions when possible.
//===----------------------------------------------------------------------===//
//
#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "SIInstrInfo.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetMachine.h"
#define DEBUG_TYPE "si-shrink-instructions"
STATISTIC(NumInstructionsShrunk,
"Number of 64-bit instruction reduced to 32-bit.");
STATISTIC(NumLiteralConstantsFolded,
"Number of literal constants folded into 32-bit instructions.");
namespace llvm {
void initializeSIShrinkInstructionsPass(PassRegistry&);
}
using namespace llvm;
namespace {
class SIShrinkInstructions : public MachineFunctionPass {
public:
static char ID;
public:
SIShrinkInstructions() : MachineFunctionPass(ID) {
}
bool runOnMachineFunction(MachineFunction &MF) override;
const char *getPassName() const override {
return "SI Shrink Instructions";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // End anonymous namespace.
INITIALIZE_PASS_BEGIN(SIShrinkInstructions, DEBUG_TYPE,
"SI Lower il Copies", false, false)
INITIALIZE_PASS_END(SIShrinkInstructions, DEBUG_TYPE,
"SI Lower il Copies", false, false)
char SIShrinkInstructions::ID = 0;
FunctionPass *llvm::createSIShrinkInstructionsPass() {
return new SIShrinkInstructions();
}
static bool isVGPR(const MachineOperand *MO, const SIRegisterInfo &TRI,
const MachineRegisterInfo &MRI) {
if (!MO->isReg())
return false;
if (TargetRegisterInfo::isVirtualRegister(MO->getReg()))
return TRI.hasVGPRs(MRI.getRegClass(MO->getReg()));
return TRI.hasVGPRs(TRI.getPhysRegClass(MO->getReg()));
}
static bool canShrink(MachineInstr &MI, const SIInstrInfo *TII,
const SIRegisterInfo &TRI,
const MachineRegisterInfo &MRI) {
const MachineOperand *Src2 = TII->getNamedOperand(MI, AMDGPU::OpName::src2);
// Can't shrink instruction with three operands.
if (Src2)
return false;
const MachineOperand *Src1 = TII->getNamedOperand(MI, AMDGPU::OpName::src1);
const MachineOperand *Src1Mod =
TII->getNamedOperand(MI, AMDGPU::OpName::src1_modifiers);
if (Src1 && (!isVGPR(Src1, TRI, MRI) || (Src1Mod && Src1Mod->getImm() != 0)))
return false;
// We don't need to check src0, all input types are legal, so just make sure
// src0 isn't using any modifiers.
if (TII->hasModifiersSet(MI, AMDGPU::OpName::src0_modifiers))
return false;
// Check output modifiers
if (TII->hasModifiersSet(MI, AMDGPU::OpName::omod))
return false;
if (TII->hasModifiersSet(MI, AMDGPU::OpName::clamp))
return false;
return true;
}
/// \brief This function checks \p MI for operands defined by a move immediate
/// instruction and then folds the literal constant into the instruction if it
/// can. This function assumes that \p MI is a VOP1, VOP2, or VOPC instruction
/// and will only fold literal constants if we are still in SSA.
static void foldImmediates(MachineInstr &MI, const SIInstrInfo *TII,
MachineRegisterInfo &MRI, bool TryToCommute = true) {
if (!MRI.isSSA())
return;
assert(TII->isVOP1(MI.getOpcode()) || TII->isVOP2(MI.getOpcode()) ||
TII->isVOPC(MI.getOpcode()));
const SIRegisterInfo &TRI = TII->getRegisterInfo();
MachineOperand *Src0 = TII->getNamedOperand(MI, AMDGPU::OpName::src0);
// Only one literal constant is allowed per instruction, so if src0 is a
// literal constant then we can't do any folding.
if ((Src0->isImm() || Src0->isFPImm()) && TII->isLiteralConstant(*Src0))
return;
// Literal constants and SGPRs can only be used in Src0, so if Src0 is an
// SGPR, we cannot commute the instruction, so we can't fold any literal
// constants.
if (Src0->isReg() && !isVGPR(Src0, TRI, MRI))
return;
// Try to fold Src0
if (Src0->isReg()) {
unsigned Reg = Src0->getReg();
MachineInstr *Def = MRI.getUniqueVRegDef(Reg);
if (Def && Def->isMoveImmediate()) {
MachineOperand &MovSrc = Def->getOperand(1);
bool ConstantFolded = false;
if (MovSrc.isImm() && isUInt<32>(MovSrc.getImm())) {
Src0->ChangeToImmediate(MovSrc.getImm());
ConstantFolded = true;
} else if (MovSrc.isFPImm()) {
const ConstantFP *CFP = MovSrc.getFPImm();
if (&CFP->getValueAPF().getSemantics() == &APFloat::IEEEsingle) {
Src0->ChangeToFPImmediate(CFP);
ConstantFolded = true;
}
}
if (ConstantFolded) {
if (MRI.use_empty(Reg))
Def->eraseFromParent();
++NumLiteralConstantsFolded;
return;
}
}
}
// We have failed to fold src0, so commute the instruction and try again.
if (TryToCommute && MI.isCommutable() && TII->commuteInstruction(&MI))
foldImmediates(MI, TII, MRI, false);
}
bool SIShrinkInstructions::runOnMachineFunction(MachineFunction &MF) {
MachineRegisterInfo &MRI = MF.getRegInfo();
const SIInstrInfo *TII =
static_cast<const SIInstrInfo *>(MF.getSubtarget().getInstrInfo());
const SIRegisterInfo &TRI = TII->getRegisterInfo();
std::vector<unsigned> I1Defs;
for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
BI != BE; ++BI) {
MachineBasicBlock &MBB = *BI;
MachineBasicBlock::iterator I, Next;
for (I = MBB.begin(); I != MBB.end(); I = Next) {
Next = std::next(I);
MachineInstr &MI = *I;
if (!TII->hasVALU32BitEncoding(MI.getOpcode()))
continue;
if (!canShrink(MI, TII, TRI, MRI)) {
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// Try commuting the instruction and see if that enables us to shrink
// it.
if (!MI.isCommutable() || !TII->commuteInstruction(&MI) ||
!canShrink(MI, TII, TRI, MRI))
continue;
}
int Op32 = AMDGPU::getVOPe32(MI.getOpcode());
// Op32 could be -1 here if we started with an instruction that had a
// a 32-bit encoding and then commuted it to an instruction that did not.
if (Op32 == -1)
continue;
if (TII->isVOPC(Op32)) {
unsigned DstReg = MI.getOperand(0).getReg();
if (TargetRegisterInfo::isVirtualRegister(DstReg)) {
// VOPC instructions can only write to the VCC register. We can't
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// force them to use VCC here, because the register allocator has
// trouble with sequences like this, which cause the allocator to run
// out of registers if vreg0 and vreg1 belong to the VCCReg register
// class:
// vreg0 = VOPC;
// vreg1 = VOPC;
// S_AND_B64 vreg0, vreg1
//
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// So, instead of forcing the instruction to write to VCC, we provide
// a hint to the register allocator to use VCC and then we we will run
// this pass again after RA and shrink it if it outputs to VCC.
MRI.setRegAllocationHint(MI.getOperand(0).getReg(), 0, AMDGPU::VCC);
continue;
}
if (DstReg != AMDGPU::VCC)
continue;
}
// We can shrink this instruction
DEBUG(dbgs() << "Shrinking "; MI.dump(); dbgs() << '\n';);
MachineInstrBuilder Inst32 =
BuildMI(MBB, I, MI.getDebugLoc(), TII->get(Op32));
// dst
Inst32.addOperand(MI.getOperand(0));
Inst32.addOperand(*TII->getNamedOperand(MI, AMDGPU::OpName::src0));
const MachineOperand *Src1 =
TII->getNamedOperand(MI, AMDGPU::OpName::src1);
if (Src1)
Inst32.addOperand(*Src1);
++NumInstructionsShrunk;
MI.eraseFromParent();
foldImmediates(*Inst32, TII, MRI);
DEBUG(dbgs() << "e32 MI = " << *Inst32 << '\n');
}
}
return false;
}