[MemorySSA] Fix existing phis when inserting defs.

Summary:
When inserting a new Def, and inserting Phis in the IDF when needed,
also mark the already existing Phis in the IDF as non-optimized, since
these may need fixing as well.
In the test attached, there is a Phi in the IDF that happens to be
trivial, and is wrongfully removed by the call to getLastDef that
follows. This is a valid situation and the existing IDF Phis need to
marked as "may need fixing" as well.
Resolves PR43044.

Reviewers: george.burgess.iv

Subscribers: Prazek, sanjoy.google, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66495

llvm-svn: 369464

1 files changed, 12 insertions, 8 deletions

diff --git a/llvm/lib/Analysis/MemorySSAUpdater.cpp b/llvm/lib/Analysis/MemorySSAUpdater.cpp
index 87818c59176..e63a9b8c341 100644
--- a/llvm/lib/Analysis/MemorySSAUpdater.cpp
+++ b/llvm/lib/Analysis/MemorySSAUpdater.cpp
@@ -341,16 +341,20 @@ void MemorySSAUpdater::insertDef(MemoryDef *MD, bool RenameUses) {
       IDFs.setDefiningBlocks(DefiningBlocks);
       IDFs.calculate(IDFBlocks);
       SmallVector<AssertingVH<MemoryPhi>, 4> NewInsertedPHIs;
-      for (auto *BBIDF : IDFBlocks)
-        if (!MSSA->getMemoryAccess(BBIDF)) {
-          auto *MPhi = MSSA->createMemoryPhi(BBIDF);
+      for (auto *BBIDF : IDFBlocks) {
+        auto *MPhi = MSSA->getMemoryAccess(BBIDF);
+        if (!MPhi) {
+          MPhi = MSSA->createMemoryPhi(BBIDF);
           NewInsertedPHIs.push_back(MPhi);
-          // Add the phis created into the IDF blocks to NonOptPhis, so they are
-          // not optimized out as trivial by the call to getPreviousDefFromEnd
-          // below. Once they are complete, all these Phis are added to the
-          // FixupList, and removed from NonOptPhis inside fixupDefs().
-          NonOptPhis.insert(MPhi);
         }
+        // Add the phis created into the IDF blocks to NonOptPhis, so they are
+        // not optimized out as trivial by the call to getPreviousDefFromEnd
+        // below. Once they are complete, all these Phis are added to the
+        // FixupList, and removed from NonOptPhis inside fixupDefs().
+        // Existing Phis in IDF may need fixing as well, and potentially be
+        // trivial before this insertion, hence add all IDF Phis. See PR43044.
+        NonOptPhis.insert(MPhi);
+      }
 
       for (auto &MPhi : NewInsertedPHIs) {
         auto *BBIDF = MPhi->getBlock();