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[LICM] Create LoopNest Invariant Code Motion (LNICM) pass

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This patch adds a new pass called LNICM which is a LoopNest version of LICM and a test case to show how LNICM works.
Basically, LNICM only hoists invariants out of loop nest (not a loop) to keep/make perfect loop nest. This enables later optimizations that require perfect loop nest.

Reviewed By: Whitney

Differential Revision: https://reviews.llvm.org/D104180
This commit is contained in:
maekawatoshiki 2021-07-20 00:31:18 +09:00
parent 9fc3416fcc
commit 10a3d40457
5 changed files with 154 additions and 6 deletions
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16
include/llvm/Transforms/Scalar/LICM.h
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@ -57,6 +57,22 @@ public:
PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR, LPMUpdater &U);
};
/// Performs LoopNest Invariant Code Motion Pass.
class LNICMPass : public PassInfoMixin<LNICMPass> {
unsigned LicmMssaOptCap;
unsigned LicmMssaNoAccForPromotionCap;
public:
LNICMPass()
: LicmMssaOptCap(SetLicmMssaOptCap),
LicmMssaNoAccForPromotionCap(SetLicmMssaNoAccForPromotionCap) {}
LNICMPass(unsigned LicmMssaOptCap, unsigned LicmMssaNoAccForPromotionCap)
: LicmMssaOptCap(LicmMssaOptCap),
LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap) {}
PreservedAnalyses run(LoopNest &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR, LPMUpdater &U);
};
} // end namespace llvm
#endif // LLVM_TRANSFORMS_SCALAR_LICM_H

2
include/llvm/Transforms/Utils/LoopUtils.h
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@ -165,7 +165,7 @@ bool hoistRegion(DomTreeNode *, AAResults *, LoopInfo *, DominatorTree *,
BlockFrequencyInfo *, TargetLibraryInfo *, Loop *,
AliasSetTracker *, MemorySSAUpdater *, ScalarEvolution *,
ICFLoopSafetyInfo *, SinkAndHoistLICMFlags &,
OptimizationRemarkEmitter *);
OptimizationRemarkEmitter *, bool);
/// This function deletes dead loops. The caller of this function needs to
/// guarantee that the loop is infact dead.

1
lib/Passes/PassRegistry.def
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@ -415,6 +415,7 @@ LOOP_PASS("canon-freeze", CanonicalizeFreezeInLoopsPass())
LOOP_PASS("dot-ddg", DDGDotPrinterPass())
LOOP_PASS("invalidate<all>", InvalidateAllAnalysesPass())
LOOP_PASS("licm", LICMPass())
LOOP_PASS("lnicm", LNICMPass())
LOOP_PASS("loop-flatten", LoopFlattenPass())
LOOP_PASS("loop-idiom", LoopIdiomRecognizePass())
LOOP_PASS("loop-instsimplify", LoopInstSimplifyPass())

38
lib/Transforms/Scalar/LICM.cpp
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@ -196,7 +196,7 @@ struct LoopInvariantCodeMotion {
bool runOnLoop(Loop *L, AAResults *AA, LoopInfo *LI, DominatorTree *DT,
BlockFrequencyInfo *BFI, TargetLibraryInfo *TLI,
TargetTransformInfo *TTI, ScalarEvolution *SE, MemorySSA *MSSA,
OptimizationRemarkEmitter *ORE);
OptimizationRemarkEmitter *ORE, bool LoopNestMode = false);
LoopInvariantCodeMotion(unsigned LicmMssaOptCap,
unsigned LicmMssaNoAccForPromotionCap)
@ -295,6 +295,33 @@ PreservedAnalyses LICMPass::run(Loop &L, LoopAnalysisManager &AM,
return PA;
}
PreservedAnalyses LNICMPass::run(LoopNest &LN, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR,
LPMUpdater &) {
// For the new PM, we also can't use OptimizationRemarkEmitter as an analysis
// pass. Function analyses need to be preserved across loop transformations
// but ORE cannot be preserved (see comment before the pass definition).
OptimizationRemarkEmitter ORE(LN.getParent());
LoopInvariantCodeMotion LICM(LicmMssaOptCap, LicmMssaNoAccForPromotionCap);
Loop &OutermostLoop = LN.getOutermostLoop();
bool Changed = LICM.runOnLoop(&OutermostLoop, &AR.AA, &AR.LI, &AR.DT, AR.BFI,
&AR.TLI, &AR.TTI, &AR.SE, AR.MSSA, &ORE, true);
if (!Changed)
return PreservedAnalyses::all();
auto PA = getLoopPassPreservedAnalyses();
PA.preserve<DominatorTreeAnalysis>();
PA.preserve<LoopAnalysis>();
if (AR.MSSA)
PA.preserve<MemorySSAAnalysis>();
return PA;
}
char LegacyLICMPass::ID = 0;
INITIALIZE_PASS_BEGIN(LegacyLICMPass, "licm", "Loop Invariant Code Motion",
false, false)
@ -347,7 +374,8 @@ llvm::SinkAndHoistLICMFlags::SinkAndHoistLICMFlags(
bool LoopInvariantCodeMotion::runOnLoop(
Loop *L, AAResults *AA, LoopInfo *LI, DominatorTree *DT,
BlockFrequencyInfo *BFI, TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
ScalarEvolution *SE, MemorySSA *MSSA, OptimizationRemarkEmitter *ORE) {
ScalarEvolution *SE, MemorySSA *MSSA, OptimizationRemarkEmitter *ORE,
bool LoopNestMode) {
bool Changed = false;
assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");
@ -414,7 +442,7 @@ bool LoopInvariantCodeMotion::runOnLoop(
if (Preheader)
Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, BFI, TLI, L,
CurAST.get(), MSSAU.get(), SE, &SafetyInfo,
*Flags.get(), ORE);
*Flags.get(), ORE, LoopNestMode);
// Now that all loop invariants have been removed from the loop, promote any
// memory references to scalars that we can.
@ -859,7 +887,7 @@ bool llvm::hoistRegion(DomTreeNode *N, AAResults *AA, LoopInfo *LI,
AliasSetTracker *CurAST, MemorySSAUpdater *MSSAU,
ScalarEvolution *SE, ICFLoopSafetyInfo *SafetyInfo,
SinkAndHoistLICMFlags &Flags,
OptimizationRemarkEmitter *ORE) {
OptimizationRemarkEmitter *ORE, bool LoopNestMode) {
// Verify inputs.
assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
CurLoop != nullptr && SafetyInfo != nullptr &&
@ -882,7 +910,7 @@ bool llvm::hoistRegion(DomTreeNode *N, AAResults *AA, LoopInfo *LI,
for (BasicBlock *BB : Worklist) {
// Only need to process the contents of this block if it is not part of a
// subloop (which would already have been processed).
if (inSubLoop(BB, CurLoop, LI))
if (!LoopNestMode && inSubLoop(BB, CurLoop, LI))
continue;
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {

103
test/Transforms/LICM/lnicm.ll Normal file
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@ -0,0 +1,103 @@
; RUN: opt -aa-pipeline=basic-aa -passes='loop(loop-interchange)' -S %s | FileCheck %s --check-prefixes INTC
; RUN: opt -aa-pipeline=basic-aa -passes='loop(lnicm,loop-interchange)' -S %s | FileCheck %s --check-prefixes LNICM,CHECK
; RUN: opt -aa-pipeline=basic-aa -passes='loop(licm,loop-interchange)' -S %s | FileCheck %s --check-prefixes LICM,CHECK
; This test represents the following function:
; void test(int x[10][10], int y[10], int *z) {
; for (int k = 0; k < 10; k++) {
; int tmp = *z;
; for (int i = 0; i < 10; i++)
; x[i][k] += y[k] + tmp;
; }
; }
; We only want to hoist the load of z out of the loop nest.
; LICM hoists the load of y[k] out of the i-loop, but LNICM doesn't do so
; to keep perfect loop nest. This enables optimizations that require
; perfect loop nest (e.g. loop-interchange) to perform.
define dso_local void @test([10 x i32]* noalias %x, i32* noalias readonly %y, i32* readonly %z) {
; CHECK-LABEL: @test(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[Z:%.*]] = load i32, i32* %z, align 4
; CHECK-NEXT: br label [[FOR_BODY3_PREHEADER:%.*]]
; LNICM: for.body.preheader:
; LICM-NOT: for.body.preheader:
; INTC-NOT: for.body.preheader:
; LNICM-NEXT: br label [[FOR_BODY:%.*]]
; CHECK: for.body:
; LNICM-NEXT: [[K:%.*]] = phi i32 [ [[INC10:%.*]], [[FOR_END:%.*]] ], [ 0, [[FOR_BODY_PREHEADER:%.*]] ]
; LNICM-NEXT: br label [[FOR_BODY3_SPLIT1:%.*]]
; LICM: [[TMP:%.*]] = load i32, i32* [[ARRAYIDX:%.*]], align 4
; LNICM: for.body3.preheader:
; LICM-NOT: for.body3.preheader:
; INTC-NOT: for.body3.preheader:
; LNICM-NEXT: br label [[FOR_BODY3:%.*]]
; CHECK: for.body3:
; LNICM-NEXT: [[I:%.*]] = phi i32 [ [[TMP3:%.*]], [[FOR_BODY3_SPLIT:%.*]] ], [ 0, [[FOR_BODY3_PREHEADER:%.*]] ]
; LNICM-NEXT: br label [[FOR_BODY_PREHEADER:%.*]]
; LNICM: for.body3.split1:
; LNICM-NEXT: [[IDXPROM:%.*]] = sext i32 [[K:%.*]] to i64
; LNICM-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i32, i32* %y, i64 [[IDXPROM:%.*]]
; LNICM-NEXT: [[TMP:%.*]] = load i32, i32* [[ARRAYIDX:%.*]], align 4
; LNICM-NEXT: [[ADD:%.*]] = add nsw i32 [[TMP:%.*]], [[Z:%.*]]
; LNICM-NEXT: [[IDXPROM4:%.*]] = sext i32 [[I:%.*]] to i64
; LNICM-NEXT: [[ARRAYIDX5:%.*]] = getelementptr inbounds [10 x i32], [10 x i32]* %x, i64 [[IDXPROM4:%.*]]
; LNICM-NEXT: [[IDXPROM6:%.*]] = sext i32 [[K:%.*]] to i64
; LNICM-NEXT: [[ARRAYIDX7:%.*]] = getelementptr inbounds [10 x i32], [10 x i32]* [[ARRAYIDX5:%.*]], i64 0, i64 [[IDXPROM6:%.*]]
; LNICM-NEXT: [[TMP2:%.*]] = load i32, i32* [[ARRAYIDX7:%.*]], align 4
; LNICM-NEXT: [[ADD8:%.*]] = add nsw i32 [[TMP2:%.*]], [[ADD:%.*]]
; LNICM-NEXT: store i32 [[ADD8:%.*]], i32* [[ARRAYIDX7:%.*]], align 4
; LNICM-NEXT: [[INC:%.*]] = add nsw i32 [[I:%.*]], 1
; LNICM-NEXT: [[CMP2:%.*]] = icmp slt i32 [[INC:%.*]], 10
; LNICM-NEXT: br label [[FOR_END:%.*]]
; LNICM: for.body3.split:
; LICM-NOT: for.body3.split:
; INTC-NOT: for.body3.split:
; LNICM-NEXT: [[TMP3:%.*]] = add nsw i32 [[I:%.*]], 1
; LNICM-NEXT: [[TMP4:%.*]] = icmp slt i32 [[TMP3:%.*]], 10
; LNICM-NEXT: br i1 [[TMP4:%.*]], label [[FOR_BODY3:%.*]], label [[FOR_END11:%.*]], !llvm.loop !0
; LNICM: for.end:
; LNICM-NEXT: [[INC10:%.*]] = add nsw i32 [[K:%.*]], 1
; LNICM-NEXT: [[CMP:%.*]] = icmp slt i32 [[INC10:%.*]], 10
; LNICM-NEXT: br i1 [[CMP:%.*]], label [[FOR_BODY:%.*]], label [[FOR_BODY3_SPLIT:%.*]], !llvm.loop !2
; LNICM: for.end11:
; LNICM-NEXT: ret void
entry:
br label %for.body
for.body:
%k.02 = phi i32 [ 0, %entry ], [ %inc10, %for.end ]
%0 = load i32, i32* %z, align 4
br label %for.body3
for.body3:
%i.01 = phi i32 [ 0, %for.body ], [ %inc, %for.body3 ]
%idxprom = sext i32 %k.02 to i64
%arrayidx = getelementptr inbounds i32, i32* %y, i64 %idxprom
%1 = load i32, i32* %arrayidx, align 4
%add = add nsw i32 %1, %0
%idxprom4 = sext i32 %i.01 to i64
%arrayidx5 = getelementptr inbounds [10 x i32], [10 x i32]* %x, i64 %idxprom4
%idxprom6 = sext i32 %k.02 to i64
%arrayidx7 = getelementptr inbounds [10 x i32], [10 x i32]* %arrayidx5, i64 0, i64 %idxprom6
%2 = load i32, i32* %arrayidx7, align 4
%add8 = add nsw i32 %2, %add
store i32 %add8, i32* %arrayidx7, align 4
%inc = add nsw i32 %i.01, 1
%cmp2 = icmp slt i32 %inc, 10
br i1 %cmp2, label %for.body3, label %for.end, !llvm.loop !0
for.end:
%inc10 = add nsw i32 %k.02, 1
%cmp = icmp slt i32 %inc10, 10
br i1 %cmp, label %for.body, label %for.end11, !llvm.loop !2
for.end11:
ret void
}
!0 = distinct !{!0, !1}
!1 = !{!"llvm.loop.mustprogress"}
!2 = distinct !{!2, !1}