[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320488 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 01fc1528681b79450137e92d89f3592b518762d7..27adcade8f12c5e3fbab15f74064a57c09f8d859 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1341,8 +1341,7 @@ static bool equivalentAddressValues(Value *A, Value *B) {
 /// select ((cmp load V1, load V2), V1, V2).
 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 +1353,26 @@ 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 *SI = cast<StoreInst>(UI);
+    IC.Builder.SetInsertPoint(SI);
+    combineStoreToNewValue(IC, *SI, NewLI);
+    IC.eraseInstFromFunction(*SI);
+  }
+  IC.replaceInstUsesWith(*LI, UndefValue::get(LI->getType()));
+  IC.eraseInstFromFunction(*LI);
   return true;
 }
 
@@ -1385,7 +1401,7 @@ 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)) {

diff --git a/test/Transforms/InstCombine/multiple-uses-load-bitcast-select.ll b/test/Transforms/InstCombine/multiple-uses-load-bitcast-select.ll
new file mode 100644 (file)
index 0000000..28509df
--- /dev/null
+++ b/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
+}
+