[HLSL] Implement array temporary support (#79382)

HLSL constant sized array function parameters do not decay to pointers.
Instead constant sized array types are preserved as unique types for
overload resolution, template instantiation and name mangling.

This implements the change by adding a new `ArrayParameterType` which
represents a non-decaying `ConstantArrayType`. The new type behaves the
same as `ConstantArrayType` except that it does not decay to a pointer.

Values of `ConstantArrayType` in HLSL decay during overload resolution
via a new `HLSLArrayRValue` cast to `ArrayParameterType`.

`ArrayParamterType` values are passed indirectly by-value to functions
in IR generation resulting in callee generated memcpy instructions.

The behavior of HLSL function calls is documented in the [draft language
specification](https://microsoft.github.io/hlsl-specs/specs/hlsl.pdf)
under the Expr.Post.Call heading.

Additionally the design of this implementation approach is documented in
[Clang's
documentation](https://clang.llvm.org/docs/HLSL/FunctionCalls.html)

Resolves #70123

1 files changed, 2 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 4410388..90324de 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -276,6 +276,7 @@ TypeEvaluationKind CodeGenFunction::getEvaluationKind(QualType type) {
     case Type::Record:
     case Type::ObjCObject:
     case Type::ObjCInterface:
+    case Type::ArrayParameter:
       return TEK_Aggregate;
 
     // We operate on atomic values according to their underlying type.
@@ -2361,6 +2362,7 @@ void CodeGenFunction::EmitVariablyModifiedType(QualType type) {
       type = cast<MemberPointerType>(ty)->getPointeeType();
       break;
 
+    case Type::ArrayParameter:
     case Type::ConstantArray:
     case Type::IncompleteArray:
       // Losing element qualification here is fine.