Fix a regression for r259736.

When SCEV expansion tries to reuse an existing value, it is needed to ensure
that using the Value at the InsertPt will not break LCSSA. The fix adds a
check that InsertPt is either inside the candidate Value's parent loop, or
the candidate Value's parent loop is nullptr.

llvm-svn: 259815

1 files changed, 10 insertions, 3 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index f95e191e5ee..86cfe2d00ab 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1652,10 +1652,17 @@ Value *SCEVExpander::expand(const SCEV *S) {
     // If S is scConstant, it may be worse to reuse an existing Value.
     if (S->getSCEVType() != scConstant && Set) {
       // Choose a Value from the set which dominates the insertPt.
+      // insertPt should be inside the Value's parent loop so as not to break
+      // the LCSSA form.
       for (auto const &Ent : *Set) {
-        if (Ent && isa<Instruction>(Ent) && S->getType() == Ent->getType() &&
-            cast<Instruction>(Ent)->getFunction() == InsertPt->getFunction() &&
-            SE.DT.dominates(cast<Instruction>(Ent), InsertPt)) {
+        Instruction *EntInst = nullptr;
+        if (Ent && isa<Instruction>(Ent) &&
+            (EntInst = cast<Instruction>(Ent)) &&
+            S->getType() == Ent->getType() &&
+            EntInst->getFunction() == InsertPt->getFunction() &&
+            SE.DT.dominates(EntInst, InsertPt) &&
+            (SE.LI.getLoopFor(EntInst->getParent()) == nullptr ||
+             SE.LI.getLoopFor(EntInst->getParent())->contains(InsertPt))) {
           V = Ent;
           break;
         }