[IndVarSimplify] Ignore unreachable users of truncs

If a trunc has a user in a block which is not reachable from entry,
we can safely perform trunc elimination as if this user didn't exist.

llvm-svn: 335816

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index ed227918055..7b07c9a3c4a 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -535,6 +535,10 @@ bool SimplifyIndvar::eliminateTrunc(TruncInst *TI) {
   // Bail if we find something different.
   SmallVector<ICmpInst *, 4> ICmpUsers;
   for (auto *U : TI->users()) {
+    // We don't care about users in unreachable blocks.
+    if (isa<Instruction>(U) &&
+        !DT->isReachableFromEntry(cast<Instruction>(U)->getParent()))
+      continue;
     if (ICmpInst *ICI = dyn_cast<ICmpInst>(U)) {
       if (ICI->getOperand(0) == TI && L->isLoopInvariant(ICI->getOperand(1))) {
         assert(L->contains(ICI->getParent()) && "LCSSA form broken?");