Legalize the Entry-point for WGSL (#5498)

* Legalize the Entry-point for WGSL

The return type of the entry-point needs to be legalized when targeting
WGSL.
This commit flattens the nested-structs of the return type and the input
parameters of the entry-point.

Most of code is copied from the legalization code for Metal. The
following functions are exactly same to the implementation for Metal or
almost same.
- flattenInputParameters() : 136 lines
- reportUnsupportedSystemAttribute() : 7 lines
- ensureResultStructHasUserSemantic() : 46 lines
- struct MapStructToFlatStruct : 176 lines
- flattenNestedStructs() : 95 lines
- maybeFlattenNestedStructs() : 42 lines
- _replaceAllReturnInst() : 19 lines
- _returnNonOverlappingAttributeIndex() : 16 lines
- _replaceAttributeOfLayout() : 23 lines
- tryConvertValue() : 41 lines
- legalizeSystemValueParameters() : 11 lines

They need to be refactored to reduce the duplication later.

The test case, `tests/compute/assoctype-lookup.slang`, had a bug that
the compute shader was trying to use the varying input/output with the
user defined semantics.

This commit removes the user defined semantics, because the compute
shaders cannot use the user defined semantics.

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/source/slang/slang-emit-c-like.cpp b/source/slang/slang-emit-c-like.cpp
index 5d04a50db..020c31fdc 100644
--- a/source/slang/slang-emit-c-like.cpp
+++ b/source/slang/slang-emit-c-like.cpp
@@ -3293,6 +3293,11 @@ void CLikeSourceEmitter::emitSemanticsUsingVarLayout(IRVarLayout* varLayout)
     }
 }
 
+void CLikeSourceEmitter::emitSemanticsPrefix(IRInst* inst)
+{
+    emitSemanticsPrefixImpl(inst);
+}
+
 void CLikeSourceEmitter::emitSemantics(IRInst* inst, bool allowOffsetLayout)
 {
     emitSemanticsImpl(inst, allowOffsetLayout);
@@ -3869,6 +3874,7 @@ void CLikeSourceEmitter::emitStructDeclarationsBlock(
                 emitPackOffsetModifier(fieldKey, fieldType, packOffsetDecoration);
             }
         }
+        emitSemanticsPrefix(fieldKey);
         emitStructFieldAttributes(structType, ff);
         emitMemoryQualifiers(fieldKey);
         emitType(fieldType, getName(fieldKey));