[llvm] r313751 - Recommit [MachineCombiner] Update instruction depths incrementally for large BBs.
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 20 04:54:37 PDT 2017
Author: fhahn
Date: Wed Sep 20 04:54:37 2017
New Revision: 313751
URL: http://llvm.org/viewvc/llvm-project?rev=313751&view=rev
Log:
Recommit [MachineCombiner] Update instruction depths incrementally for large BBs.
This version of the patch fixes an off-by-one error causing PR34596. We
do not need to use std::next(BlockIter) when calling updateDepths, as
BlockIter already points to the next element.
Original commit message:
> For large basic blocks with lots of combinable instructions, the
> MachineTraceMetrics computations in MachineCombiner can dominate the compile
> time, as computing the trace information is quadratic in the number of
> instructions in a BB and it's relevant successors/predecessors.
> In most cases, knowing the instruction depth should be enough to make
> combination decisions. As we already iterate over all instructions in a basic
> block, the instruction depth can be computed incrementally. This reduces the
> cost of machine-combine drastically in cases where lots of instructions
> are combined. The major drawback is that AFAIK, computing the critical path
> length cannot be done incrementally. Therefore we only compute
> instruction depths incrementally, for basic blocks with more
> instructions than inc_threshold. The -machine-combiner-inc-threshold
> option can be used to set the threshold and allows for easier
> experimenting and checking if using incremental updates for all basic
> blocks has any impact on the performance.
>
> Reviewers: sanjoy, Gerolf, MatzeB, efriedma, fhahn
>
> Reviewed By: fhahn
>
> Subscribers: kiranchandramohan, javed.absar, efriedma, llvm-commits
>
> Differential Revision: https://reviews.llvm.org/D36619
Modified:
llvm/trunk/include/llvm/CodeGen/MachineTraceMetrics.h
llvm/trunk/lib/CodeGen/MachineCombiner.cpp
llvm/trunk/lib/CodeGen/MachineTraceMetrics.cpp
llvm/trunk/test/CodeGen/AArch64/machine-combiner.ll
llvm/trunk/test/CodeGen/X86/machine-combiner.ll
llvm/trunk/test/CodeGen/X86/mul-constant-result.ll
Modified: llvm/trunk/include/llvm/CodeGen/MachineTraceMetrics.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/MachineTraceMetrics.h?rev=313751&r1=313750&r2=313751&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/MachineTraceMetrics.h (original)
+++ llvm/trunk/include/llvm/CodeGen/MachineTraceMetrics.h Wed Sep 20 04:54:37 2017
@@ -366,6 +366,12 @@ public:
SparseSet<LiveRegUnit> &RegUnits);
void updateDepth(const MachineBasicBlock *, const MachineInstr&,
SparseSet<LiveRegUnit> &RegUnits);
+
+ /// Updates the depth of the instructions from Start to End.
+ void updateDepths(MachineBasicBlock::iterator Start,
+ MachineBasicBlock::iterator End,
+ SparseSet<LiveRegUnit> &RegUnits);
+
};
/// Strategies for selecting traces.
Modified: llvm/trunk/lib/CodeGen/MachineCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineCombiner.cpp?rev=313751&r1=313750&r2=313751&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineCombiner.cpp Wed Sep 20 04:54:37 2017
@@ -22,6 +22,7 @@
#include "llvm/CodeGen/MachineTraceMetrics.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetSchedule.h"
+#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
@@ -34,6 +35,11 @@ using namespace llvm;
STATISTIC(NumInstCombined, "Number of machineinst combined");
+static cl::opt<unsigned>
+inc_threshold("machine-combiner-inc-threshold", cl::Hidden,
+ cl::desc("Incremental depth computation will be used for basic "
+ "blocks with more instructions."), cl::init(500));
+
namespace {
class MachineCombiner : public MachineFunctionPass {
const TargetInstrInfo *TII;
@@ -73,7 +79,7 @@ private:
SmallVectorImpl<MachineInstr *> &InsInstrs,
SmallVectorImpl<MachineInstr *> &DelInstrs,
DenseMap<unsigned, unsigned> &InstrIdxForVirtReg,
- MachineCombinerPattern Pattern);
+ MachineCombinerPattern Pattern, bool SlackIsAccurate);
bool preservesResourceLen(MachineBasicBlock *MBB,
MachineTraceMetrics::Trace BlockTrace,
SmallVectorImpl<MachineInstr *> &InsInstrs,
@@ -247,7 +253,8 @@ bool MachineCombiner::improvesCriticalPa
SmallVectorImpl<MachineInstr *> &InsInstrs,
SmallVectorImpl<MachineInstr *> &DelInstrs,
DenseMap<unsigned, unsigned> &InstrIdxForVirtReg,
- MachineCombinerPattern Pattern) {
+ MachineCombinerPattern Pattern,
+ bool SlackIsAccurate) {
assert(TSchedModel.hasInstrSchedModelOrItineraries() &&
"Missing machine model\n");
// NewRoot is the last instruction in the \p InsInstrs vector.
@@ -258,7 +265,7 @@ bool MachineCombiner::improvesCriticalPa
unsigned NewRootDepth = getDepth(InsInstrs, InstrIdxForVirtReg, BlockTrace);
unsigned RootDepth = BlockTrace.getInstrCycles(*Root).Depth;
- DEBUG(dbgs() << "DEPENDENCE DATA FOR " << Root << "\n";
+ DEBUG(dbgs() << "DEPENDENCE DATA FOR " << *Root << "\n";
dbgs() << " NewRootDepth: " << NewRootDepth << "\n";
dbgs() << " RootDepth: " << RootDepth << "\n");
@@ -281,17 +288,18 @@ bool MachineCombiner::improvesCriticalPa
RootLatency += TSchedModel.computeInstrLatency(I);
unsigned RootSlack = BlockTrace.getInstrSlack(*Root);
-
+ unsigned NewCycleCount = NewRootDepth + NewRootLatency;
+ unsigned OldCycleCount = RootDepth + RootLatency +
+ (SlackIsAccurate ? RootSlack : 0);
DEBUG(dbgs() << " NewRootLatency: " << NewRootLatency << "\n";
dbgs() << " RootLatency: " << RootLatency << "\n";
- dbgs() << " RootSlack: " << RootSlack << "\n";
+ dbgs() << " RootSlack: " << RootSlack << " SlackIsAccurate="
+ << SlackIsAccurate << "\n";
dbgs() << " NewRootDepth + NewRootLatency = "
- << NewRootDepth + NewRootLatency << "\n";
+ << NewCycleCount << "\n";
dbgs() << " RootDepth + RootLatency + RootSlack = "
- << RootDepth + RootLatency + RootSlack << "\n";);
-
- unsigned NewCycleCount = NewRootDepth + NewRootLatency;
- unsigned OldCycleCount = RootDepth + RootLatency + RootSlack;
+ << OldCycleCount << "\n";
+ );
return NewCycleCount <= OldCycleCount;
}
@@ -354,17 +362,44 @@ bool MachineCombiner::doSubstitute(unsig
return false;
}
+/// Inserts InsInstrs and deletes DelInstrs. Incrementally updates instruction
+/// depths if requested.
+///
+/// \param MBB basic block to insert instructions in
+/// \param MI current machine instruction
+/// \param InsInstrs new instructions to insert in \p MBB
+/// \param DelInstrs instruction to delete from \p MBB
+/// \param MinInstr is a pointer to the machine trace information
+/// \param RegUnits set of live registers, needed to compute instruction depths
+/// \param IncrementalUpdate if true, compute instruction depths incrementally,
+/// otherwise invalidate the trace
static void insertDeleteInstructions(MachineBasicBlock *MBB, MachineInstr &MI,
SmallVector<MachineInstr *, 16> InsInstrs,
SmallVector<MachineInstr *, 16> DelInstrs,
- MachineTraceMetrics *Traces) {
+ MachineTraceMetrics::Ensemble *MinInstr,
+ SparseSet<LiveRegUnit> &RegUnits,
+ bool IncrementalUpdate) {
for (auto *InstrPtr : InsInstrs)
MBB->insert((MachineBasicBlock::iterator)&MI, InstrPtr);
- for (auto *InstrPtr : DelInstrs)
+
+ for (auto *InstrPtr : DelInstrs) {
InstrPtr->eraseFromParentAndMarkDBGValuesForRemoval();
- ++NumInstCombined;
- Traces->invalidate(MBB);
- Traces->verifyAnalysis();
+ // Erase all LiveRegs defined by the removed instruction
+ for (auto I = RegUnits.begin(); I != RegUnits.end(); ) {
+ if (I->MI == InstrPtr)
+ I = RegUnits.erase(I);
+ else
+ I++;
+ }
+ }
+
+ if (IncrementalUpdate)
+ for (auto *InstrPtr : InsInstrs)
+ MinInstr->updateDepth(MBB, *InstrPtr, RegUnits);
+ else
+ MinInstr->invalidate(MBB);
+
+ NumInstCombined++;
}
/// Substitute a slow code sequence with a faster one by
@@ -378,9 +413,16 @@ bool MachineCombiner::combineInstruction
bool Changed = false;
DEBUG(dbgs() << "Combining MBB " << MBB->getName() << "\n");
+ bool IncrementalUpdate = false;
auto BlockIter = MBB->begin();
+ auto LastUpdate = BlockIter;
// Check if the block is in a loop.
const MachineLoop *ML = MLI->getLoopFor(MBB);
+ if (!MinInstr)
+ MinInstr = Traces->getEnsemble(MachineTraceMetrics::TS_MinInstrCount);
+
+ SparseSet<LiveRegUnit> RegUnits;
+ RegUnits.setUniverse(TRI->getNumRegUnits());
while (BlockIter != MBB->end()) {
auto &MI = *BlockIter++;
@@ -419,9 +461,6 @@ bool MachineCombiner::combineInstruction
SmallVector<MachineInstr *, 16> InsInstrs;
SmallVector<MachineInstr *, 16> DelInstrs;
DenseMap<unsigned, unsigned> InstrIdxForVirtReg;
- if (!MinInstr)
- MinInstr = Traces->getEnsemble(MachineTraceMetrics::TS_MinInstrCount);
- Traces->verifyAnalysis();
TII->genAlternativeCodeSequence(MI, P, InsInstrs, DelInstrs,
InstrIdxForVirtReg);
unsigned NewInstCount = InsInstrs.size();
@@ -436,23 +475,41 @@ bool MachineCombiner::combineInstruction
if (ML && TII->isThroughputPattern(P))
SubstituteAlways = true;
+ if (IncrementalUpdate) {
+ // Update depths since the last incremental update.
+ MinInstr->updateDepths(LastUpdate, BlockIter, RegUnits);
+ LastUpdate = BlockIter;
+ }
+
// Substitute when we optimize for codesize and the new sequence has
// fewer instructions OR
// the new sequence neither lengthens the critical path nor increases
// resource pressure.
if (SubstituteAlways || doSubstitute(NewInstCount, OldInstCount)) {
- insertDeleteInstructions(MBB, MI, InsInstrs, DelInstrs, Traces);
+ insertDeleteInstructions(MBB, MI, InsInstrs, DelInstrs, MinInstr,
+ RegUnits, IncrementalUpdate);
// Eagerly stop after the first pattern fires.
Changed = true;
break;
} else {
- // Calculating the trace metrics may be expensive,
- // so only do this when necessary.
+ // For big basic blocks, we only compute the full trace the first time
+ // we hit this. We do not invalidate the trace, but instead update the
+ // instruction depths incrementally.
+ // NOTE: Only the instruction depths up to MI are accurate. All other
+ // trace information is not updated.
MachineTraceMetrics::Trace BlockTrace = MinInstr->getTrace(MBB);
+ Traces->verifyAnalysis();
if (improvesCriticalPathLen(MBB, &MI, BlockTrace, InsInstrs, DelInstrs,
- InstrIdxForVirtReg, P) &&
+ InstrIdxForVirtReg, P,
+ !IncrementalUpdate) &&
preservesResourceLen(MBB, BlockTrace, InsInstrs, DelInstrs)) {
- insertDeleteInstructions(MBB, MI, InsInstrs, DelInstrs, Traces);
+ if (MBB->size() > inc_threshold)
+ // Use incremental depth updates for basic blocks above treshold
+ IncrementalUpdate = true;
+
+ insertDeleteInstructions(MBB, MI, InsInstrs, DelInstrs, MinInstr,
+ RegUnits, IncrementalUpdate);
+
// Eagerly stop after the first pattern fires.
Changed = true;
break;
@@ -467,6 +524,8 @@ bool MachineCombiner::combineInstruction
}
}
+ if (Changed && IncrementalUpdate)
+ Traces->invalidate(MBB);
return Changed;
}
Modified: llvm/trunk/lib/CodeGen/MachineTraceMetrics.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineTraceMetrics.cpp?rev=313751&r1=313750&r2=313751&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineTraceMetrics.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineTraceMetrics.cpp Wed Sep 20 04:54:37 2017
@@ -824,6 +824,14 @@ updateDepth(const MachineBasicBlock *MBB
updateDepth(BlockInfo[MBB->getNumber()], UseMI, RegUnits);
}
+void MachineTraceMetrics::Ensemble::
+updateDepths(MachineBasicBlock::iterator Start,
+ MachineBasicBlock::iterator End,
+ SparseSet<LiveRegUnit> &RegUnits) {
+ for (; Start != End; Start++)
+ updateDepth(Start->getParent(), *Start, RegUnits);
+}
+
/// Compute instruction depths for all instructions above or in MBB in its
/// trace. This assumes that the trace through MBB has already been computed.
void MachineTraceMetrics::Ensemble::
Modified: llvm/trunk/test/CodeGen/AArch64/machine-combiner.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/machine-combiner.ll?rev=313751&r1=313750&r2=313751&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/AArch64/machine-combiner.ll (original)
+++ llvm/trunk/test/CodeGen/AArch64/machine-combiner.ll Wed Sep 20 04:54:37 2017
@@ -1,5 +1,10 @@
; RUN: llc -mtriple=aarch64-gnu-linux -mcpu=cortex-a57 -enable-unsafe-fp-math -disable-post-ra < %s | FileCheck %s
+; Incremental updates of the instruction depths should be enough for this test
+; case.
+; RUN: llc -mtriple=aarch64-gnu-linux -mcpu=cortex-a57 -enable-unsafe-fp-math \
+; RUN: -disable-post-ra -machine-combiner-inc-threshold=0 < %s | FileCheck %s
+
; Verify that the first two adds are independent regardless of how the inputs are
; commuted. The destination registers are used as source registers for the third add.
Modified: llvm/trunk/test/CodeGen/X86/machine-combiner.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/machine-combiner.ll?rev=313751&r1=313750&r2=313751&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/machine-combiner.ll (original)
+++ llvm/trunk/test/CodeGen/X86/machine-combiner.ll Wed Sep 20 04:54:37 2017
@@ -1,6 +1,11 @@
; RUN: llc -mtriple=x86_64-unknown-unknown -mcpu=x86-64 -mattr=sse -enable-unsafe-fp-math < %s | FileCheck %s --check-prefix=SSE
; RUN: llc -mtriple=x86_64-unknown-unknown -mcpu=x86-64 -mattr=avx -enable-unsafe-fp-math < %s | FileCheck %s --check-prefix=AVX
+; Incremental updates of the instruction depths should be enough for this test
+; case.
+; RUN: llc -mtriple=x86_64-unknown-unknown -mcpu=x86-64 -mattr=sse -enable-unsafe-fp-math -machine-combiner-inc-threshold=0 < %s | FileCheck %s --check-prefix=SSE
+; RUN: llc -mtriple=x86_64-unknown-unknown -mcpu=x86-64 -mattr=avx -enable-unsafe-fp-math -machine-combiner-inc-threshold=0 < %s | FileCheck %s --check-prefix=AVX
+
; Verify that the first two adds are independent regardless of how the inputs are
; commuted. The destination registers are used as source registers for the third add.
Modified: llvm/trunk/test/CodeGen/X86/mul-constant-result.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/mul-constant-result.ll?rev=313751&r1=313750&r2=313751&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/mul-constant-result.ll (original)
+++ llvm/trunk/test/CodeGen/X86/mul-constant-result.ll Wed Sep 20 04:54:37 2017
@@ -1,6 +1,9 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc < %s -mtriple=i686-unknown | FileCheck %s --check-prefix=X86
-; RUN: llc < %s -mtriple=x86_64-unknown -mcpu=haswell| FileCheck %s --check-prefix=X64-HSW
+
+; Incremental updates of the instruction depths should be enough for this test
+; case.
+; RUN: llc < %s -mtriple=x86_64-unknown -mcpu=haswell -machine-combiner-inc-threshold=0| FileCheck %s --check-prefix=X64-HSW
; Function Attrs: norecurse nounwind readnone uwtable
define i32 @mult(i32, i32) local_unnamed_addr #0 {
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