[clang] 8ebbb20 - [HLSL] Add an lvalue to rvalue cast when appropriate for HLSLElementwiseCast and HLSLAggregateSplatCast (#163828)

[via cfe-commits]

Author: Sarah Spall
Date: 2025-10-16T11:28:13-07:00
New Revision: 8ebbb20dffe2b3bbe43a21faacaa7b5e208b1e40

URL: https://github.com/llvm/llvm-project/commit/8ebbb20dffe2b3bbe43a21faacaa7b5e208b1e40
DIFF: https://github.com/llvm/llvm-project/commit/8ebbb20dffe2b3bbe43a21faacaa7b5e208b1e40.diff

LOG: [HLSL] Add an lvalue to rvalue cast when appropriate for HLSLElementwiseCast and HLSLAggregateSplatCast (#163828)

When the Sub expression of an HLSLAggregateSplatCast is an LValue insert
an LValue to RValue cast; done using DefaultLvalueConversion.
When the Sub expression of an HLSLElementwiseCast is an LValue and not a
record or an array insert an LValue to RValue cast.
Arrays were already handled correctly using an HLSLArrayRValue cast.

DefaultLvalueConversion is used to add the LValue to RValue cast when
appropriate and does not emit one when the expression is a record.

Update existing test which was broken by this change. Add two new tests
for HLSLElementwiseCast showing the lack of lvalue to rvalue cast for a
struct and showing the lvalue to rvalue cast for a vector.

Closes #163593

Added: 
    

Modified: 
    clang/lib/Sema/SemaCast.cpp
    clang/test/SemaHLSL/Language/AggregateSplatCasts.hlsl
    clang/test/SemaHLSL/Language/ElementwiseCasts.hlsl

Removed: 
    


################################################################################
diff  --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index ddf17d8551428..5360f8a2908bf 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -2927,6 +2927,8 @@ bool CastOperation::CheckHLSLCStyleCast(CheckedConversionKind CCK) {
       SrcExpr = Self.ImpCastExprToType(
           SrcExpr.get(), Self.Context.getArrayParameterType(SrcTy),
           CK_HLSLArrayRValue, VK_PRValue, nullptr, CCK);
+    else
+      SrcExpr = Self.DefaultLvalueConversion(SrcExpr.get());
     Kind = CK_HLSLElementwiseCast;
     return true;
   }
@@ -2935,6 +2937,7 @@ bool CastOperation::CheckHLSLCStyleCast(CheckedConversionKind CCK) {
   // If the relative order of this and the HLSLElementWise cast checks
   // are changed, it might change which cast handles what in a few cases
   if (Self.HLSL().CanPerformAggregateSplatCast(SrcExpr.get(), DestType)) {
+    SrcExpr = Self.DefaultLvalueConversion(SrcExpr.get());
     const VectorType *VT = SrcTy->getAs<VectorType>();
     // change splat from vec1 case to splat from scalar
     if (VT && VT->getNumElements() == 1)

diff  --git a/clang/test/SemaHLSL/Language/AggregateSplatCasts.hlsl b/clang/test/SemaHLSL/Language/AggregateSplatCasts.hlsl
index e5a851c50caf8..623fca0ef9aca 100644
--- a/clang/test/SemaHLSL/Language/AggregateSplatCasts.hlsl
+++ b/clang/test/SemaHLSL/Language/AggregateSplatCasts.hlsl
@@ -3,8 +3,9 @@
 // splat from vec1 to vec
 // CHECK-LABEL: call1
 // CHECK: CStyleCastExpr {{.*}} 'int3':'vector<int, 3>' <HLSLAggregateSplatCast>
-// CHECK-NEXT: ImplicitCastExpr {{.*}} 'int' lvalue <FloatingToIntegral> part_of_explicit_cast
-// CHECK-NEXT: ImplicitCastExpr {{.*}} 'float' lvalue <HLSLVectorTruncation> part_of_explicit_cast
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'int' <FloatingToIntegral> part_of_explicit_cast
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'float' <HLSLVectorTruncation> part_of_explicit_cast
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'float1':'vector<float, 1>' <LValueToRValue> part_of_explicit_cast
 // CHECK-NEXT: DeclRefExpr {{.*}} 'float1':'vector<float, 1>' lvalue Var {{.*}} 'A' 'float1':'vector<float, 1>'
 export void call1() {
   float1 A = {1.0};
@@ -21,7 +22,7 @@ struct S {
 // splat from scalar to aggregate
 // CHECK-LABEL: call2
 // CHECK: CStyleCastExpr {{.*}} 'S' <HLSLAggregateSplatCast>
-// CHECK-NEXt: IntegerLiteral {{.*}} 'int' 5
+// CHECK-NEXT: IntegerLiteral {{.*}} 'int' 5
 export void call2() {
   S s = (S)5; 
 }

diff  --git a/clang/test/SemaHLSL/Language/ElementwiseCasts.hlsl b/clang/test/SemaHLSL/Language/ElementwiseCasts.hlsl
index 563d3f02a1485..8481cfc1b18e2 100644
--- a/clang/test/SemaHLSL/Language/ElementwiseCasts.hlsl
+++ b/clang/test/SemaHLSL/Language/ElementwiseCasts.hlsl
@@ -21,3 +21,27 @@ export void call2() {
   float B[1] = {1.0};
   B = (float[1])A;
 }
+
+struct S {
+  int A;
+  float F;
+};
+
+// cast from a struct
+// CHECK-LABEL: call3
+// CHECK: CStyleCastExpr {{.*}} 'int[2]' <HLSLElementwiseCast>
+// CHECK-NEXT: DeclRefExpr {{.*}} 'S' lvalue Var {{.*}} 'SS' 'S'
+export void call3() {
+  S SS = {1,1.0};
+  int A[2] = (int[2])SS;
+}
+
+// cast from a vector
+// CHECK-LABEL: call4
+// CHECK: CStyleCastExpr {{.*}} 'float[3]' <HLSLElementwiseCast>
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'int3':'vector<int, 3>' <LValueToRValue> part_of_explicit_cast
+// CHECK-NEXT: DeclRefExpr {{.*}} 'int3':'vector<int, 3>' lvalue Var {{.*}} 'A' 'int3'
+export void call4() {
+  int3 A = {1,2,3};
+  float B[3] = (float[3])A;
+}