Fix an ordering bug in the scalarizer.

I've added a new test case that causes the scalarizer to try and use
dead-and-erased values - caused by the basic blocks not being in
domination order within the function. To fix this, instead of iterating
through the blocks in function order, I walk them in reverse post order.

Differential Revision: https://reviews.llvm.org/D52540

llvm-svn: 344128

1 files changed, 7 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/Scalarizer.cpp b/llvm/lib/Transforms/Scalar/Scalarizer.cpp
index 34ed126155b..2f873abca66 100644
--- a/llvm/lib/Transforms/Scalar/Scalarizer.cpp
+++ b/llvm/lib/Transforms/Scalar/Scalarizer.cpp
@@ -14,6 +14,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/PostOrderIterator.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Analysis/VectorUtils.h"
@@ -289,8 +290,12 @@ bool Scalarizer::runOnFunction(Function &F) {
   if (skipFunction(F))
     return false;
   assert(Gathered.empty() && Scattered.empty());
-  for (BasicBlock &BB : F) {
-    for (BasicBlock::iterator II = BB.begin(), IE = BB.end(); II != IE;) {
+
+  // To ensure we replace gathered components correctly we need to do an ordered
+  // traversal of the basic blocks in the function.
+  ReversePostOrderTraversal<BasicBlock *> RPOT(&F.getEntryBlock());
+  for (BasicBlock *BB : RPOT) {
+    for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE;) {
       Instruction *I = &*II;
       bool Done = visit(I);
       ++II;