Self review

Author: spall

clang/lib/CodeGen/CGExprScalar.cpp

@@ -2796,17 +2796,20 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     return Builder.CreateExtractElement(Vec, Zero, "cast.vtrunc");
   }
   case CK_HLSLSplatCast: {
+    // This code should only handle splatting from vectors of length 1.
     assert(DestTy->isVectorType() && "Destination type must be a vector.");
     auto *DestVecTy = DestTy->getAs<VectorType>();
     QualType SrcTy = E->getType();
     SourceLocation Loc = CE->getExprLoc();
     Value *V = Visit(const_cast<Expr *>(E));
-    if (auto *VecTy = SrcTy->getAs<VectorType>()) {
-      assert(VecTy->getNumElements() == 1 && "Invalid HLSL splat cast.");
-      V = CGF.Builder.CreateExtractElement(V, (uint64_t)0, "vec.load");
-      SrcTy = VecTy->getElementType();
-    }
-    assert(SrcTy->isScalarType() && "Invalid HLSL splat cast.");
+    assert(SrcTy->isVectorType() && "Invalid HLSL splat cast.");
+
+    auto *VecTy = SrcTy->getAs<VectorType>();
+    assert(VecTy->getNumElements() == 1 && "Invalid HLSL splat cast.");
+
+    V = CGF.Builder.CreateExtractElement(V, (uint64_t)0, "vec.load");
+    SrcTy = VecTy->getElementType();
+
     Value *Cast =
         EmitScalarConversion(V, SrcTy, DestVecTy->getElementType(), Loc);
     return Builder.CreateVectorSplat(DestVecTy->getNumElements(), Cast,

clang/lib/Sema/SemaHLSL.cpp

@@ -2814,12 +2814,13 @@ bool SemaHLSL::CanPerformSplat(Expr *Src, QualType DestTy) {
     return false;
 
   const VectorType *SrcVecTy = SrcTy->getAs<VectorType>();
-  if (!(SrcTy->isScalarType() || (SrcVecTy && SrcVecTy->getNumElements() == 1)))
-    return false;
-
   if (SrcVecTy)
     SrcTy = SrcVecTy->getElementType();
 
+  // Src isn't a scalar or a vector of length 1
+  if (!SrcTy->isScalarType() && !(SrcVecTy && SrcVecTy->getNumElements() == 1))
+    return false;
+
   llvm::SmallVector<QualType> DestTypes;
   BuildFlattenedTypeList(DestTy, DestTypes);
 

clang/test/SemaHLSL/Language/SplatCasts.hlsl

@@ -0,0 +1,25 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -finclude-default-header -fnative-half-type %s -ast-dump | FileCheck %s
+
+// splat from vec1 to vec
+// CHECK-LABEL: call1
+// CHECK: CStyleCastExpr {{.*}} 'int3':'vector<int, 3>' <HLSLSplatCast>
+// CHECK-NEXT: DeclRefExpr {{.*}} 'float1':'vector<float, 1>' lvalue Var {{.*}} 'A' 'float1':'vector<float, 1>'
+export void call1() {
+  float1 A = {1.0};
+  int3 B = (int3)A;
+}
+
+struct S {
+  int A;
+  float B;
+  int C;
+  float D;
+};
+
+// splat from scalar to aggregate
+// CHECK-LABEL: call2
+// CHECK: CStyleCastExpr {{.*}} 'S' <HLSLSplatCast>
+// CHECK-NEXt: IntegerLiteral {{.*}} 'int' 5
+export void call2() {
+  S s = (S)5; 
+}