[SROA] Correctly invalidate analyses when dead instructions deleted

Summary:
SROA can fail in rewriting alloca but still rewrite a phi resulting
in dead instruction elimination. The Changed flag was not being set
correctly, resulting in downstream passes using stale analyses.
The included test case will assert during the second BDCE pass as a
result.

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D39921

llvm-svn: 318677

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index 6de6c8cce2c..2d668f940fb 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -4243,8 +4243,9 @@ bool SROA::runOnAlloca(AllocaInst &AI) {
 ///
 /// We also record the alloca instructions deleted here so that they aren't
 /// subsequently handed to mem2reg to promote.
-void SROA::deleteDeadInstructions(
+bool SROA::deleteDeadInstructions(
     SmallPtrSetImpl<AllocaInst *> &DeletedAllocas) {
+  bool Changed = false;
   while (!DeadInsts.empty()) {
     Instruction *I = DeadInsts.pop_back_val();
     DEBUG(dbgs() << "Deleting dead instruction: " << *I << "\n");
@@ -4270,7 +4271,9 @@ void SROA::deleteDeadInstructions(
 
     ++NumDeleted;
     I->eraseFromParent();
+    Changed = true;
   }
+  return Changed;
 }
 
 /// \brief Promote the allocas, using the best available technique.
@@ -4312,7 +4315,7 @@ PreservedAnalyses SROA::runImpl(Function &F, DominatorTree &RunDT,
   do {
     while (!Worklist.empty()) {
       Changed |= runOnAlloca(*Worklist.pop_back_val());
-      deleteDeadInstructions(DeletedAllocas);
+      Changed |= deleteDeadInstructions(DeletedAllocas);
 
       // Remove the deleted allocas from various lists so that we don't try to
       // continue processing them.