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[IndVarSimplify] Fix poison-safety when reusing instructions #80458

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Feb 5, 2024
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[IndVarSimplify] Fix poison-safety when reusing instructions #80458

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18 changes: 16 additions & 2 deletions llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
Expand Down Expand Up @@ -713,8 +714,11 @@ bool SimplifyIndvar::replaceFloatIVWithIntegerIV(Instruction *UseInst) {
bool SimplifyIndvar::eliminateIdentitySCEV(Instruction *UseInst,
Instruction *IVOperand) {
if (!SE->isSCEVable(UseInst->getType()) ||
(UseInst->getType() != IVOperand->getType()) ||
(SE->getSCEV(UseInst) != SE->getSCEV(IVOperand)))
UseInst->getType() != IVOperand->getType())
return false;

const SCEV *UseSCEV = SE->getSCEV(UseInst);
if (UseSCEV != SE->getSCEV(IVOperand))
return false;

// getSCEV(X) == getSCEV(Y) does not guarantee that X and Y are related in the
Expand Down Expand Up @@ -742,6 +746,16 @@ bool SimplifyIndvar::eliminateIdentitySCEV(Instruction *UseInst,
if (!LI->replacementPreservesLCSSAForm(UseInst, IVOperand))
return false;

// Make sure the operand is not more poisonous than the instruction.
if (!impliesPoison(IVOperand, UseInst)) {
SmallVector<Instruction *> DropPoisonGeneratingInsts;
if (!SE->canReuseInstruction(UseSCEV, IVOperand, DropPoisonGeneratingInsts))
return false;

for (Instruction *I : DropPoisonGeneratingInsts)
I->dropPoisonGeneratingFlagsAndMetadata();
}

LLVM_DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n');

SE->forgetValue(UseInst);
Expand Down
4 changes: 2 additions & 2 deletions llvm/test/Transforms/IndVarSimplify/pr55925.ll
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Expand Up @@ -18,9 +18,9 @@ define void @test(ptr %p) personality ptr undef {
; CHECK-NEXT: [[RES:%.*]] = invoke i32 @foo(i32 returned [[TMP0]])
; CHECK-NEXT: to label [[LOOP_LATCH]] unwind label [[EXIT:%.*]]
; CHECK: loop.latch:
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[INDVARS_IV]] to i32
; CHECK-NEXT: [[TMP2:%.*]] = call i32 @foo(i32 [[TMP1]])
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add i64 [[INDVARS_IV]], 1
; CHECK-NEXT: br label [[LOOP]]
; CHECK: exit:
; CHECK-NEXT: [[LP:%.*]] = landingpad { ptr, i32 }
Expand Down Expand Up @@ -64,8 +64,8 @@ define void @test_critedge(i1 %c, ptr %p) personality ptr undef {
; CHECK-NEXT: br label [[LOOP_LATCH]]
; CHECK: loop.latch:
; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ [[TMP1]], [[LOOP_INVOKE]] ], [ 0, [[LOOP_OTHER]] ]
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[TMP2:%.*]] = call i32 @foo(i32 [[PHI]])
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add i64 [[INDVARS_IV]], 1
; CHECK-NEXT: br label [[LOOP]]
; CHECK: exit:
; CHECK-NEXT: [[LP:%.*]] = landingpad { ptr, i32 }
Expand Down
6 changes: 4 additions & 2 deletions llvm/test/Transforms/IndVarSimplify/pr79861.ll
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Expand Up @@ -12,7 +12,9 @@ define void @or_disjoint() {
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 2, [[ENTRY:%.*]] ], [ [[IV_DEC:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[OR:%.*]] = or disjoint i64 [[IV]], 1
; CHECK-NEXT: call void @use(i64 [[OR]])
; CHECK-NEXT: [[ADD:%.*]] = add nuw nsw i64 [[IV]], 1
; CHECK-NEXT: [[SEL:%.*]] = select i1 false, i64 [[OR]], i64 [[ADD]]
; CHECK-NEXT: call void @use(i64 [[SEL]])
; CHECK-NEXT: [[IV_DEC]] = add nsw i64 [[IV]], -1
; CHECK-NEXT: [[EXIT_COND:%.*]] = icmp eq i64 [[IV_DEC]], 0
; CHECK-NEXT: br i1 [[EXIT_COND]], label [[EXIT:%.*]], label [[LOOP]]
Expand Down Expand Up @@ -44,7 +46,7 @@ define void @add_nowrap_flags(i64 %n) {
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_INC:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[ADD1:%.*]] = add nuw nsw i64 [[IV]], 123
; CHECK-NEXT: [[ADD1:%.*]] = add i64 [[IV]], 123
; CHECK-NEXT: call void @use(i64 [[ADD1]])
; CHECK-NEXT: [[IV_INC]] = add i64 [[IV]], 1
; CHECK-NEXT: [[EXIT_COND:%.*]] = icmp eq i64 [[IV_INC]], [[N]]
Expand Down
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