| Issue |
183461
|
| Summary |
[HLSL] Explicitly casting an array to a scalar performs an HLSLElementwiseCast
|
| Labels |
clang:frontend,
HLSL
|
| Assignees |
|
| Reporter |
Icohedron
|
Explicitly casting an array to a scalar performs an elementwise conversion (`HLSLElementwiseCast`) in Clang but not in DXC.
The [hlsl-spec](https://github.com/microsoft/hlsl-specs/blob/58965078aa95b157767b035f5566c76318c70dfd/specs/language/conversions.tex#L124-L125) also states that an elementwise conversion is aggregate -> aggregate, and does not mention aggregate -> scalar.
Repro: https://hlsl.godbolt.org/z/qGoTPMshK
Given the HLSL:
```hlsl
void fn() {
int A[4] = {1, 2, 3, 4};
int I = (int)A;
}
```
The following AST is produced for the VarDecl `int I = (int)A;`:
```
`-VarDecl <col:5, col:18> col:9 I 'int' cinit
`-CStyleCastExpr <col:13, col:18> 'int' <HLSLElementwiseCast>
`-ImplicitCastExpr <col:18> 'int[4]' <HLSLArrayRValue> part_of_explicit_cast
`-DeclRefExpr <col:18> 'int[4]' lvalue Var 0x1c037468 'A' 'int[4]'
```
DXC produces the following AST for the same VarDecl:
```
`-VarDecl <col:5, col:18> col:9 I 'int' cinit
`-ImplicitCastExpr <col:13, col:18> 'int' <LValueToRValue>
`-CStyleCastExpr <col:13, col:18> 'int' lvalue <NoOp>
`-ImplicitCastExpr <col:18> 'int' <FlatConversion>
`-ImplicitCastExpr <col:18> 'int [4]' <LValueToRValue>
`-DeclRefExpr <col:18> 'int [4]' lvalue Var 0x5a64f371e528 'A' 'int [4]'
```
While this seems harmless and produces the expected behavior, it affects the implementation of the new constant _expression_ evaluator which now has to explicitly account for the possibility of `HLSLElementwiseCast` emitting a scalar instead of an aggregate type.
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