[IndVars] Set Changed if sinkUnusedInvariants changes IR. PR38863

Currently, `sinkUnusedInvariants` does not set Changed flag even if it makes
changes in the IR. There is no clear evidence that it can cause a crash, but it
looks highly suspicious and likely invalid.

Differential Revision: https://reviews.llvm.org/D51777
Reviewed By: skatkov

llvm-svn: 341777

1 files changed, 9 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 0b2583565f4..5d73723e0d6 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -150,7 +150,7 @@ class IndVarSimplify {
   Value *linearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
                                    PHINode *IndVar, SCEVExpander &Rewriter);
 
-  void sinkUnusedInvariants(Loop *L);
+  bool sinkUnusedInvariants(Loop *L);
 
 public:
   IndVarSimplify(LoopInfo *LI, ScalarEvolution *SE, DominatorTree *DT,
@@ -2476,13 +2476,14 @@ linearFunctionTestReplace(Loop *L,
 /// If there's a single exit block, sink any loop-invariant values that
 /// were defined in the preheader but not used inside the loop into the
 /// exit block to reduce register pressure in the loop.
-void IndVarSimplify::sinkUnusedInvariants(Loop *L) {
+bool IndVarSimplify::sinkUnusedInvariants(Loop *L) {
   BasicBlock *ExitBlock = L->getExitBlock();
-  if (!ExitBlock) return;
+  if (!ExitBlock) return false;
 
   BasicBlock *Preheader = L->getLoopPreheader();
-  if (!Preheader) return;
+  if (!Preheader) return false;
 
+  bool MadeAnyChanges = false;
   BasicBlock::iterator InsertPt = ExitBlock->getFirstInsertionPt();
   BasicBlock::iterator I(Preheader->getTerminator());
   while (I != Preheader->begin()) {
@@ -2552,10 +2553,13 @@ void IndVarSimplify::sinkUnusedInvariants(Loop *L) {
       Done = true;
     }
 
+    MadeAnyChanges = true;
     ToMove->moveBefore(*ExitBlock, InsertPt);
     if (Done) break;
     InsertPt = ToMove->getIterator();
   }
+
+  return MadeAnyChanges;
 }
 
 //===----------------------------------------------------------------------===//
@@ -2649,7 +2653,7 @@ bool IndVarSimplify::run(Loop *L) {
 
   // Loop-invariant instructions in the preheader that aren't used in the
   // loop may be sunk below the loop to reduce register pressure.
-  sinkUnusedInvariants(L);
+  Changed |= sinkUnusedInvariants(L);
 
   // rewriteFirstIterationLoopExitValues does not rely on the computation of
   // trip count and therefore can further simplify exit values in addition to