[HLSL] Implement output parameter (#101083)

HLSL output parameters are denoted with the `inout` and `out` keywords
in the function declaration. When an argument to an output parameter is
constructed a temporary value is constructed for the argument.

For `inout` pamameters the argument is initialized via copy-initialization
from the argument lvalue expression to the parameter type. For `out`
parameters the argument is not initialized before the call.

In both cases on return of the function the temporary value is written
back to the argument lvalue expression through an implicit assignment
binary operator with casting as required.

This change introduces a new HLSLOutArgExpr ast node which represents
the output argument behavior. The OutArgExpr has three defined children:
- An OpaqueValueExpr of the argument lvalue expression.
- An OpaqueValueExpr of the copy-initialized parameter.
- A BinaryOpExpr assigning the first with the value of the second.

Fixes #87526

---------

Co-authored-by: Damyan Pepper <damyanp@microsoft.com>
Co-authored-by: John McCall <rjmccall@gmail.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/lib/Serialization/ASTWriterStmt.cpp b/clang/lib/Serialization/ASTWriterStmt.cpp
index c292d0a..8371366 100644
--- a/clang/lib/Serialization/ASTWriterStmt.cpp
+++ b/clang/lib/Serialization/ASTWriterStmt.cpp
@@ -2911,6 +2911,19 @@ void ASTStmtWriter::VisitOpenACCLoopConstruct(OpenACCLoopConstruct *S) {
 }
 
 //===----------------------------------------------------------------------===//
+// HLSL Constructs/Directives.
+//===----------------------------------------------------------------------===//
+
+void ASTStmtWriter::VisitHLSLOutArgExpr(HLSLOutArgExpr *S) {
+  VisitExpr(S);
+  Record.AddStmt(S->getOpaqueArgLValue());
+  Record.AddStmt(S->getCastedTemporary());
+  Record.AddStmt(S->getWritebackCast());
+  Record.writeBool(S->isInOut());
+  Code = serialization::EXPR_HLSL_OUT_ARG;
+}
+
+//===----------------------------------------------------------------------===//
 // ASTWriter Implementation
 //===----------------------------------------------------------------------===//