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AMDGPU: Remove SIFixSGPRLiveRanges pass 

Summary:
This pass is unnecessary and overly conservative. It was motivated by
situations like

  def %vreg0:SGPR_32
  ...
if-block:
  ..
  def %vreg1:SGPR_32
  ...
else-block:
  ...
  use %vreg0:SGPR_32
  ...

and similar situations with uses after the non-uniform control flow, where
we are not allowed to assign %vreg0 and %vreg1 to the same physical register,
even though in the original, thread/workitem-based CFG, it looks like the
live ranges of these registers do not overlap.

However, by the time register allocation runs, we have moved to a wave-based
CFG that accurately represents the fact that the wave may run through both
the if- and the else-block. So the live ranges of %vreg0 and %vreg1 already
overlap even without the SIFixSGPRLiveRanges pass.

In addition to proving this change correct, I have tested it with Piglit
and a small number of other tests.

Reviewers: arsenm, tstellarAMD

Subscribers: MatzeB, arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D19041

llvm-svn: 266345
This commit is contained in:
Nicolai Haehnle 2016-04-14 17:42:29 +00:00
parent 19f0f5177d
commit 723b73b4eb
5 changed files with 1 additions and 243 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
llvm/lib/Target/AMDGPU/AMDGPU.h
View File

@ -48,7 +48,6 @@ FunctionPass *createSIWholeQuadModePass();
FunctionPass *createSILowerControlFlowPass();
FunctionPass *createSIFixControlFlowLiveIntervalsPass();
FunctionPass *createSIFixSGPRCopiesPass();
FunctionPass *createSIFixSGPRLiveRangesPass();
FunctionPass *createSICodeEmitterPass(formatted_raw_ostream &OS);
FunctionPass *createSIInsertNopsPass();
FunctionPass *createSIInsertWaitsPass();
@ -93,9 +92,6 @@ FunctionPass *createAMDGPUAnnotateUniformValues();
void initializeSIFixControlFlowLiveIntervalsPass(PassRegistry&);
extern char &SIFixControlFlowLiveIntervalsID;
void initializeSIFixSGPRLiveRangesPass(PassRegistry&);
extern char &SIFixSGPRLiveRangesID;
void initializeAMDGPUAnnotateUniformValuesPass(PassRegistry&);
extern char &AMDGPUAnnotateUniformValuesPassID;

7
llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
View File

@ -48,7 +48,6 @@ extern "C" void LLVMInitializeAMDGPUTarget() {
initializeSILowerI1CopiesPass(*PR);
initializeSIFixSGPRCopiesPass(*PR);
initializeSIFoldOperandsPass(*PR);
initializeSIFixSGPRLiveRangesPass(*PR);
initializeSIFixControlFlowLiveIntervalsPass(*PR);
initializeSILoadStoreOptimizerPass(*PR);
initializeAMDGPUAnnotateKernelFeaturesPass(*PR);
@ -351,16 +350,10 @@ void GCNPassConfig::addPreRegAlloc() {
}
void GCNPassConfig::addFastRegAlloc(FunctionPass *RegAllocPass) {
addPass(&SIFixSGPRLiveRangesID);
TargetPassConfig::addFastRegAlloc(RegAllocPass);
}
void GCNPassConfig::addOptimizedRegAlloc(FunctionPass *RegAllocPass) {
// We want to run this after LiveVariables is computed to avoid computing them
// twice.
// FIXME: We shouldn't disable the verifier here. r249087 introduced a failure
// that needs to be fixed.
insertPass(&LiveVariablesID, &SIFixSGPRLiveRangesID, /*VerifyAfter=*/false);
TargetPassConfig::addOptimizedRegAlloc(RegAllocPass);
}

1
llvm/lib/Target/AMDGPU/CMakeLists.txt
View File

@ -48,7 +48,6 @@ add_llvm_target(AMDGPUCodeGen
SIAnnotateControlFlow.cpp
SIFixControlFlowLiveIntervals.cpp
SIFixSGPRCopies.cpp
SIFixSGPRLiveRanges.cpp
SIFoldOperands.cpp
SIFrameLowering.cpp
SIInsertNopsPass.cpp

230
llvm/lib/Target/AMDGPU/SIFixSGPRLiveRanges.cpp
View File

@ -1,230 +0,0 @@
//===-- SIFixSGPRLiveRanges.cpp - Fix SGPR live ranges ----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \file SALU instructions ignore the execution mask, so we need to modify the
/// live ranges of the registers they define in some cases.
///
/// The main case we need to handle is when a def is used in one side of a
/// branch and not another. For example:
///
/// %def
/// IF
/// ...
/// ...
/// ELSE
/// %use
/// ...
/// ENDIF
///
/// Here we need the register allocator to avoid assigning any of the defs
/// inside of the IF to the same register as %def. In traditional live
/// interval analysis %def is not live inside the IF branch, however, since
/// SALU instructions inside of IF will be executed even if the branch is not
/// taken, there is the chance that one of the instructions will overwrite the
/// value of %def, so the use in ELSE will see the wrong value.
///
/// The strategy we use for solving this is to add an extra use after the ENDIF:
///
/// %def
/// IF
/// ...
/// ...
/// ELSE
/// %use
/// ...
/// ENDIF
/// %use
///
/// Adding this use will make the def live throughout the IF branch, which is
/// what we want.
#include "AMDGPU.h"
#include "SIInstrInfo.h"
#include "SIRegisterInfo.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachinePostDominators.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
#define DEBUG_TYPE "si-fix-sgpr-live-ranges"
namespace {
class SIFixSGPRLiveRanges : public MachineFunctionPass {
public:
static char ID;
public:
SIFixSGPRLiveRanges() : MachineFunctionPass(ID) {
initializeSIFixSGPRLiveRangesPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
const char *getPassName() const override {
return "SI Fix SGPR live ranges";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LiveVariables>();
AU.addPreserved<LiveVariables>();
AU.addRequired<MachinePostDominatorTree>();
AU.addPreserved<MachinePostDominatorTree>();
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // End anonymous namespace.
INITIALIZE_PASS_BEGIN(SIFixSGPRLiveRanges, DEBUG_TYPE,
"SI Fix SGPR Live Ranges", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveVariables)
INITIALIZE_PASS_DEPENDENCY(MachinePostDominatorTree)
INITIALIZE_PASS_END(SIFixSGPRLiveRanges, DEBUG_TYPE,
"SI Fix SGPR Live Ranges", false, false)
char SIFixSGPRLiveRanges::ID = 0;
char &llvm::SIFixSGPRLiveRangesID = SIFixSGPRLiveRanges::ID;
FunctionPass *llvm::createSIFixSGPRLiveRangesPass() {
return new SIFixSGPRLiveRanges();
}
static bool hasOnlyScalarBr(const MachineBasicBlock *MBB,
const SIInstrInfo *TII) {
for (MachineBasicBlock::const_iterator I = MBB->getFirstTerminator(),
E = MBB->end(); I != E; ++I) {
if (!TII->isSOPP(*I))
return false;
}
return true;
}
bool SIFixSGPRLiveRanges::runOnMachineFunction(MachineFunction &MF) {
MachineRegisterInfo &MRI = MF.getRegInfo();
const SIInstrInfo *TII =
static_cast<const SIInstrInfo *>(MF.getSubtarget().getInstrInfo());
const SIRegisterInfo *TRI = static_cast<const SIRegisterInfo *>(
MF.getSubtarget().getRegisterInfo());
bool MadeChange = false;
MachinePostDominatorTree *PDT = &getAnalysis<MachinePostDominatorTree>();
SmallVector<unsigned, 16> SGPRLiveRanges;
LiveVariables *LV = &getAnalysis<LiveVariables>();
MachineBasicBlock *Entry = &MF.front();
// Use a depth first order so that in SSA, we encounter all defs before
// uses. Once the defs of the block have been found, attempt to insert
// SGPR_USE instructions in successor blocks if required.
for (MachineBasicBlock *MBB : depth_first(Entry)) {
for (const MachineInstr &MI : *MBB) {
for (const MachineOperand &MO : MI.defs()) {
// We should never see a live out def of a physical register, so we also
// do not need to worry about implicit_defs().
unsigned Def = MO.getReg();
if (TargetRegisterInfo::isVirtualRegister(Def)) {
if (TRI->isSGPRClass(MRI.getRegClass(Def))) {
// Only consider defs that are live outs. We don't care about def /
// use within the same block.
// LiveVariables does not consider registers that are only used in a
// phi in a sucessor block as live out, unlike LiveIntervals.
//
// This is OK because SIFixSGPRCopies replaced any SGPR phis with
// VGPRs.
if (LV->isLiveOut(Def, *MBB))
SGPRLiveRanges.push_back(Def);
}
}
}
}
if (MBB->succ_size() < 2 || hasOnlyScalarBr(MBB, TII))
continue;
// We have structured control flow, so the number of successors should be
// two.
assert(MBB->succ_size() == 2);
MachineBasicBlock *SuccA = *MBB->succ_begin();
MachineBasicBlock *SuccB = *(++MBB->succ_begin());
MachineBasicBlock *NCD = PDT->findNearestCommonDominator(SuccA, SuccB);
if (!NCD)
continue;
MachineBasicBlock::iterator NCDTerm = NCD->getFirstTerminator();
if (NCDTerm != NCD->end() && NCDTerm->getOpcode() == AMDGPU::SI_ELSE) {
assert(NCD->succ_size() == 2);
// We want to make sure we insert the Use after the ENDIF, not after
// the ELSE.
NCD = PDT->findNearestCommonDominator(*NCD->succ_begin(),
*(++NCD->succ_begin()));
}
for (unsigned Reg : SGPRLiveRanges) {
// FIXME: We could be smarter here. If the register is Live-In to one
// block, but the other doesn't have any SGPR defs, then there won't be a
// conflict. Also, if the branch condition is uniform then there will be
// no conflict.
bool LiveInToA = LV->isLiveIn(Reg, *SuccA);
bool LiveInToB = LV->isLiveIn(Reg, *SuccB);
if (!LiveInToA && !LiveInToB) {
DEBUG(dbgs() << PrintReg(Reg, TRI, 0)
<< " is live into neither successor\n");
continue;
}
if (LiveInToA && LiveInToB) {
DEBUG(dbgs() << PrintReg(Reg, TRI, 0)
<< " is live into both successors\n");
continue;
}
// This interval is live in to one successor, but not the other, so
// we need to update its range so it is live in to both.
DEBUG(dbgs() << "Possible SGPR conflict detected for "
<< PrintReg(Reg, TRI, 0)
<< " BB#" << SuccA->getNumber()
<< ", BB#" << SuccB->getNumber()
<< " with NCD = BB#" << NCD->getNumber() << '\n');
assert(TargetRegisterInfo::isVirtualRegister(Reg) &&
"Not expecting to extend live range of physreg");
// FIXME: Need to figure out how to update LiveRange here so this pass
// will be able to preserve LiveInterval analysis.
MachineInstr *NCDSGPRUse =
BuildMI(*NCD, NCD->getFirstNonPHI(), DebugLoc(),
TII->get(AMDGPU::SGPR_USE))
.addReg(Reg, RegState::Implicit);
MadeChange = true;
LV->HandleVirtRegUse(Reg, NCD, NCDSGPRUse);
DEBUG(NCDSGPRUse->dump());
}
}
return MadeChange;
}

2
llvm/test/CodeGen/AMDGPU/subreg-coalescer-undef-use.ll
View File

@ -12,7 +12,7 @@ target triple="amdgcn--"
; CHECK-NEXT: s_and_saveexec_b64 s[2:3], vcc
; CHECK-NEXT: s_xor_b64 s[2:3], exec, s[2:3]
; BB0_1:
; CHECK: s_load_dword s6, s[0:1], 0xa
; CHECK: s_load_dword s0, s[0:1], 0xa
; CHECK-NEXT: s_waitcnt lgkmcnt(0)
; BB0_2:
; CHECK: s_or_b64 exec, exec, s[2:3]