[llvm] 652cd7c - [InstCombine] Fix user iterator invalidation in bitcast of phi transform

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-01-14T20:38:10+01:00
New Revision: 652cd7c1007aa5a13ad9864fadc939c5710c5199

URL: https://github.com/llvm/llvm-project/commit/652cd7c1007aa5a13ad9864fadc939c5710c5199
DIFF: https://github.com/llvm/llvm-project/commit/652cd7c1007aa5a13ad9864fadc939c5710c5199.diff

LOG: [InstCombine] Fix user iterator invalidation in bitcast of phi transform

This fixes the issue encountered in D71164. Instead of using a
range-based for, manually iterate over the users and advance the
iterator beforehand, so we do not skip any users due to iterator
invalidation.

Differential Revision: https://reviews.llvm.org/D72657

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
    llvm/test/Transforms/InstCombine/bitcast-phi-uselistorder.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 3ba56bbe53e0..f6c7bb5d4479 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -2344,7 +2344,10 @@ Instruction *InstCombiner::optimizeBitCastFromPhi(CastInst &CI, PHINode *PN) {
   Instruction *RetVal = nullptr;
   for (auto *OldPN : OldPhiNodes) {
     PHINode *NewPN = NewPNodes[OldPN];
-    for (User *V : OldPN->users()) {
+    for (auto It = OldPN->user_begin(), End = OldPN->user_end(); It != End; ) {
+      User *V = *It;
+      // We may remove this user, advance to avoid iterator invalidation.
+      ++It;
       if (auto *SI = dyn_cast<StoreInst>(V)) {
         assert(SI->isSimple() && SI->getOperand(0) == OldPN);
         Builder.SetInsertPoint(SI);

diff  --git a/llvm/test/Transforms/InstCombine/bitcast-phi-uselistorder.ll b/llvm/test/Transforms/InstCombine/bitcast-phi-uselistorder.ll
index d1af21f6c4d5..d5489484bddf 100644
--- a/llvm/test/Transforms/InstCombine/bitcast-phi-uselistorder.ll
+++ b/llvm/test/Transforms/InstCombine/bitcast-phi-uselistorder.ll
@@ -8,16 +8,13 @@ define double @test(i1 %c, i64* %p) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br i1 [[C:%.*]], label [[IF:%.*]], label [[END:%.*]]
 ; CHECK:       if:
-; CHECK-NEXT:    [[LOAD:%.*]] = load i64, i64* bitcast (double* @Q to i64*), align 8
-; CHECK-NEXT:    [[TMP0:%.*]] = bitcast i64 [[LOAD]] to double
-; CHECK-NEXT:    [[PHITMP:%.*]] = bitcast i64 [[LOAD]] to double
+; CHECK-NEXT:    [[LOAD1:%.*]] = load double, double* @Q, align 8
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[TMP1:%.*]] = phi double [ 0.000000e+00, [[ENTRY:%.*]] ], [ [[TMP0]], [[IF]] ]
-; CHECK-NEXT:    [[PHI:%.*]] = phi double [ 0.000000e+00, [[ENTRY]] ], [ [[PHITMP]], [[IF]] ]
-; CHECK-NEXT:    [[TMP2:%.*]] = bitcast i64* [[P:%.*]] to double*
-; CHECK-NEXT:    store double [[TMP1]], double* [[TMP2]], align 8
-; CHECK-NEXT:    ret double [[PHI]]
+; CHECK-NEXT:    [[TMP0:%.*]] = phi double [ 0.000000e+00, [[ENTRY:%.*]] ], [ [[LOAD1]], [[IF]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i64* [[P:%.*]] to double*
+; CHECK-NEXT:    store double [[TMP0]], double* [[TMP1]], align 8
+; CHECK-NEXT:    ret double [[TMP0]]
 ;
 entry:
   br i1 %c, label %if, label %end