[InstCombine] Fix PR35618: Instcombine hangs on single minmax load bitcast.

If we have pattern `store (load(bitcast(select (cmp(V1, V2), &V1,
&V2)))), bitcast)`, but the load is used in other instructions, it leads
to looping in InstCombiner. Patch adds additional check that all users
of the load instructions are stores and then replaces all uses of load
instruction by the new one with new type.

Reviewers: RKSimon, spatel, majnemer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D41072

llvm-svn: 320483

1 files changed, 17 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 01fc1528681..9f00e6f8358 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1354,9 +1354,24 @@ bool removeBitcastsFromLoadStoreOnMinMax(InstCombiner &IC, StoreInst &SI) {
   if (!isMinMaxWithLoads(LoadAddr))
     return false;
 
+  if (!all_of(LI->users(), [LI](User *U) {
+        auto *SI = dyn_cast<StoreInst>(U);
+        return SI && SI->getPointerOperand() != LI &&
+               !SI->getPointerOperand()->isSwiftError();
+      }))
+    return false;
+
+  IC.Builder.SetInsertPoint(LI);
   LoadInst *NewLI = combineLoadToNewType(
       IC, *LI, LoadAddr->getType()->getPointerElementType());
-  combineStoreToNewValue(IC, SI, NewLI);
+  // Replace all the stores with stores of the newly loaded value.
+  for (auto *UI : LI->users()) {
+    auto *SI = cast<StoreInst>(UI);
+    IC.Builder.SetInsertPoint(SI);
+    combineStoreToNewValue(IC, *SI, NewLI);
+    IC.eraseInstFromFunction(*SI);
+  }
+  IC.Worklist.Add(LI);
   return true;
 }
 
@@ -1385,7 +1400,7 @@ Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
     return eraseInstFromFunction(SI);
 
   if (removeBitcastsFromLoadStoreOnMinMax(*this, SI))
-    return eraseInstFromFunction(SI);
+    return nullptr;
 
   // Replace GEP indices if possible.
   if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Ptr, SI)) {