[llvm-branch-commits] [llvm] 94dcc1d - [IndVarSimplify] Fix poison-safety when reusing instructions (#80458)

[Tom Stellard via llvm-branch-commits]

Author: Nikita Popov
Date: 2024-02-20T16:44:46-08:00
New Revision: 94dcc1d6ae0912910c1a001da54ca64171d36374

URL: https://github.com/llvm/llvm-project/commit/94dcc1d6ae0912910c1a001da54ca64171d36374
DIFF: https://github.com/llvm/llvm-project/commit/94dcc1d6ae0912910c1a001da54ca64171d36374.diff

LOG: [IndVarSimplify] Fix poison-safety when reusing instructions (#80458)

IndVars may replace an instruction with one of its operands, if they
have the same SCEV expression. However, such a replacement may be more
poisonous.

First, check whether the operand being poison implies that the
instruction is also poison, in which case the replacement is always
safe. If this fails, check whether SCEV can determine that reusing the
instruction is safe, using the same check as SCEVExpander.

Fixes https://github.com/llvm/llvm-project/issues/79861.

(cherry picked from commit 7d2b6f0b355bc98bbe3aa5bae83316a708da33ee)

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
    llvm/test/Transforms/IndVarSimplify/pr55925.ll
    llvm/test/Transforms/IndVarSimplify/pr79861.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 0ed3324a27b6c9..1b142f14d81139 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -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"
@@ -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
@@ -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);

diff  --git a/llvm/test/Transforms/IndVarSimplify/pr55925.ll b/llvm/test/Transforms/IndVarSimplify/pr55925.ll
index 420fc209949d4f..312a8295ccdc9f 100644
--- a/llvm/test/Transforms/IndVarSimplify/pr55925.ll
+++ b/llvm/test/Transforms/IndVarSimplify/pr55925.ll
@@ -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 }
@@ -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 }

diff  --git a/llvm/test/Transforms/IndVarSimplify/pr79861.ll b/llvm/test/Transforms/IndVarSimplify/pr79861.ll
index 7e267d04c94cc8..66250944961397 100644
--- a/llvm/test/Transforms/IndVarSimplify/pr79861.ll
+++ b/llvm/test/Transforms/IndVarSimplify/pr79861.ll
@@ -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]]
@@ -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]]