[PATCH] D72657: [InstCombine] Fix user iterator invalidation in bitcast of phi transform

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: spatel, lebedev.ri.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

This fixes the issue encountered in D71164 <https://reviews.llvm.org/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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72657

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


Index: llvm/test/Transforms/InstCombine/bitcast-phi-uselistorder.ll
===================================================================
--- llvm/test/Transforms/InstCombine/bitcast-phi-uselistorder.ll
+++ llvm/test/Transforms/InstCombine/bitcast-phi-uselistorder.ll
@@ -8,16 +8,13 @@
 ; 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
Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -2344,7 +2344,10 @@
   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);


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