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

Summary:
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: 320499

2 files changed, 51 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 01fc1528681..fbbdfaa04dd 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1339,10 +1339,10 @@ static bool equivalentAddressValues(Value *A, Value *B) {
 /// Converts store (bitcast (load (bitcast (select ...)))) to
 /// store (load (select ...)), where select is minmax:
 /// select ((cmp load V1, load V2), V1, V2).
-bool removeBitcastsFromLoadStoreOnMinMax(InstCombiner &IC, StoreInst &SI) {
+static bool removeBitcastsFromLoadStoreOnMinMax(InstCombiner &IC,
+                                                StoreInst &SI) {
   // bitcast?
-  Value *StoreAddr;
-  if (!match(SI.getPointerOperand(), m_BitCast(m_Value(StoreAddr))))
+  if (!match(SI.getPointerOperand(), m_BitCast(m_Value())))
     return false;
   // load? integer?
   Value *LoadAddr;
@@ -1354,9 +1354,26 @@ bool removeBitcastsFromLoadStoreOnMinMax(InstCombiner &IC, StoreInst &SI) {
   if (!isMinMaxWithLoads(LoadAddr))
     return false;
 
+  if (!all_of(LI->users(), [LI, LoadAddr](User *U) {
+        auto *SI = dyn_cast<StoreInst>(U);
+        return SI && SI->getPointerOperand() != LI &&
+               peekThroughBitcast(SI->getPointerOperand()) != LoadAddr &&
+               !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 *USI = cast<StoreInst>(UI);
+    IC.Builder.SetInsertPoint(USI);
+    combineStoreToNewValue(IC, *USI, NewLI);
+    if (USI != &SI)
+      IC.eraseInstFromFunction(*cast<Instruction>(UI));
+  }
+  IC.Worklist.Remove(LI);
   return true;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/multiple-uses-load-bitcast-select.ll b/llvm/test/Transforms/InstCombine/multiple-uses-load-bitcast-select.ll
new file mode 100644
index 00000000000..28509df6d2f
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/multiple-uses-load-bitcast-select.ll
@@ -0,0 +1,30 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S -data-layout="E-m:e-i1:8:16-i8:8:16-i64:64-f128:64-v128:64-a:8:16-n32:64" | FileCheck %s
+
+define void @PR35618(i64* %st1, double* %st2) {
+; CHECK-LABEL: @PR35618(
+; CHECK-NEXT:    [[Y1:%.*]] = alloca double, align 8
+; CHECK-NEXT:    [[Z1:%.*]] = alloca double, align 8
+; CHECK-NEXT:    [[LD1:%.*]] = load double, double* [[Y1]], align 8
+; CHECK-NEXT:    [[LD2:%.*]] = load double, double* [[Z1]], align 8
+; CHECK-NEXT:    [[TMP10:%.*]] = fcmp olt double [[LD1]], [[LD2]]
+; CHECK-NEXT:    [[TMP121:%.*]] = select i1 [[TMP10]], double [[LD1]], double [[LD2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i64* [[ST1:%.*]] to double*
+; CHECK-NEXT:    store double [[TMP121]], double* [[TMP1]], align 8
+; CHECK-NEXT:    store double [[TMP121]], double* [[ST2:%.*]], align 8
+; CHECK-NEXT:    ret void
+;
+  %y1 = alloca double
+  %z1 = alloca double
+  %ld1 = load double, double* %y1
+  %ld2 = load double, double* %z1
+  %tmp10 = fcmp olt double %ld1, %ld2
+  %sel = select i1 %tmp10, double* %y1, double* %z1
+  %tmp11 = bitcast double* %sel to i64*
+  %tmp12 = load i64, i64* %tmp11
+  store i64 %tmp12, i64* %st1
+  %bc = bitcast double* %st2 to i64*
+  store i64 %tmp12, i64* %bc
+  ret void
+}
+