Implement specialization constant support in numthreads / local_size (#5963)

* Allow using specialization constants in numthreads attribute

* Add support for GLSL local_size_x_id syntax

* Fix overeager specialization constant parsing

* Add diagnostics for specialization constant numthreads

* Remove unused variable

* Fix local_size_x_id not finding existing specialization constant

* Allow materializeGetWorkGroupSize to reference specialization constants

* Use SpvOpExecutionModeId for modes that require it

* Cleanup specialization constant numthreads code

* Add tests for specialization constant work group sizes

* Fix implicit Slang::Int -> int32_t cast

* Fix querying thread group size in reflection API

---------

Co-authored-by: Yong He <yonghe@outlook.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/source/slang/slang-emit-glsl.cpp b/source/slang/slang-emit-glsl.cpp
index 23fff37ac..0dab07cfc 100644
--- a/source/slang/slang-emit-glsl.cpp
+++ b/source/slang/slang-emit-glsl.cpp
@@ -1335,7 +1335,8 @@ void GLSLSourceEmitter::emitEntryPointAttributesImpl(
     auto emitLocalSizeLayout = [&]()
     {
         Int sizeAlongAxis[kThreadGroupAxisCount];
-        getComputeThreadGroupSize(irFunc, sizeAlongAxis);
+        Int specializationConstantIds[kThreadGroupAxisCount];
+        getComputeThreadGroupSize(irFunc, sizeAlongAxis, specializationConstantIds);
 
         m_writer->emit("layout(");
         char const* axes[] = {"x", "y", "z"};
@@ -1345,8 +1346,17 @@ void GLSLSourceEmitter::emitEntryPointAttributesImpl(
                 m_writer->emit(", ");
             m_writer->emit("local_size_");
             m_writer->emit(axes[ii]);
-            m_writer->emit(" = ");
-            m_writer->emit(sizeAlongAxis[ii]);
+
+            if (specializationConstantIds[ii] >= 0)
+            {
+                m_writer->emit("_id = ");
+                m_writer->emit(specializationConstantIds[ii]);
+            }
+            else
+            {
+                m_writer->emit(" = ");
+                m_writer->emit(sizeAlongAxis[ii]);
+            }
         }
         m_writer->emit(") in;\n");
     };