[DSE] Check write location in IsRedundantStore (llvm#93400)

Fix llvm#93298.

Author: eaeltsin

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

@@ -2109,10 +2109,12 @@ struct DSEState {
         if (auto *MemSetI = dyn_cast<MemSetInst>(UpperInst)) {
           if (auto *SI = dyn_cast<StoreInst>(DefInst)) {
             // MemSetInst must have a write location.
-            MemoryLocation UpperLoc = *getLocForWrite(UpperInst);
+            auto UpperLoc = getLocForWrite(UpperInst);
+            if (!UpperLoc)
+              return false;
             int64_t InstWriteOffset = 0;
             int64_t DepWriteOffset = 0;
-            auto OR = isOverwrite(UpperInst, DefInst, UpperLoc, *MaybeDefLoc,
+            auto OR = isOverwrite(UpperInst, DefInst, *UpperLoc, *MaybeDefLoc,
                                   InstWriteOffset, DepWriteOffset);
             Value *StoredByte = isBytewiseValue(SI->getValueOperand(), DL);
             return StoredByte && StoredByte == MemSetI->getOperand(1) &&

llvm/test/Transforms/DeadStoreElimination/simple.ll

@@ -790,3 +790,16 @@ define i32 @test48(ptr %P, ptr noalias %Q, ptr %R) {
   %l = load i32, ptr %R
   ret i32 %l
 }
+
+define void @test49() {
+; CHECK-LABEL: @test49(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr readonly null, i8 0, i64 0, i1 false)
+; CHECK-NEXT:    store ptr null, ptr null, align 8
+; CHECK-NEXT:    ret void
+;
+bb:
+  call void @llvm.memset.p0.i64(ptr readonly null, i8 0, i64 0, i1 false)
+  store ptr null, ptr null, align 8
+  ret void
+}