MemCpyOpt: When merging memsets also merge the trivial case of two memsets...

MemCpyOpt: When merging memsets also merge the trivial case of two memsets with the same destination.

The testcase is from PR19092, but I think the bug described there is actually a clang issue.

llvm-svn: 203489

llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp

@@ -75,6 +75,13 @@ static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
                             const DataLayout &TD) {
   Ptr1 = Ptr1->stripPointerCasts();
   Ptr2 = Ptr2->stripPointerCasts();
+
+  // Handle the trivial case first.
+  if (Ptr1 == Ptr2) {
+    Offset = 0;
+    return true;
+  }
+
   GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
   GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);
 

llvm/test/Transforms/MemCpyOpt/form-memset.ll

@@ -272,3 +272,15 @@ define void @test9() nounwind {
 ; CHECK-LABEL: @test9(
 ; CHECK: call void @llvm.memset.p0i8.i64(i8* bitcast ([16 x i64]* @test9buf to i8*), i8 -1, i64 16, i32 16, i1 false)
 }
+
+; PR19092
+define void @test10(i8* nocapture %P) nounwind {
+  tail call void @llvm.memset.p0i8.i64(i8* %P, i8 0, i64 42, i32 1, i1 false)
+  tail call void @llvm.memset.p0i8.i64(i8* %P, i8 0, i64 23, i32 1, i1 false)
+  ret void
+; CHECK-LABEL: @test10(
+; CHECK-NOT: memset
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %P, i8 0, i64 42, i32 1, i1 false)
+; CHECK-NOT: memset
+; CHECK: ret void
+}