expose value of constant integers in module reflection (#6367)

* Expose value of constant integers in module reflection

This commit adds `VariableReflection::getDefaultValueInt` to get the value of a variable if it is a compile-time constant integer.
TODO: currently it works only if the initializer expression is an integer literal, references to other constant values are not handled.

* Update VarDecl folded constant value during DeclBodyVisitor

Constant folding for integer values is already done internally by _validateCircularVarDefinition, this just reuses the result.

* Address review comments & formatting

* Formatting

---------

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

7 files changed, 63 insertions, 6 deletions

diff --git a/examples/reflection-api/compute-simple.slang b/examples/reflection-api/compute-simple.slang
index 3d8872180..00d45d857 100644
--- a/examples/reflection-api/compute-simple.slang
+++ b/examples/reflection-api/compute-simple.slang
@@ -1,5 +1,8 @@
 // compute-simple.slang
 
+static const uint THREADGROUP_SIZE_X = 8;
+static const uint THREADGROUP_SIZE_Y = THREADGROUP_SIZE_X;
+
 struct ImageProcessingOptions
 {
     float3 tintColor;
@@ -10,7 +13,7 @@ struct ImageProcessingOptions
 }
 
 [shader("compute")]
-[numthreads(8, 8)]
+[numthreads(THREADGROUP_SIZE_X, THREADGROUP_SIZE_Y)]
 void processImage(
     uint3 threadID : SV_DispatchThreadID,
     uniform Texture2D inputImage,
diff --git a/examples/reflection-api/main.cpp b/examples/reflection-api/main.cpp
index c072c641b..2ff4475bf 100644
--- a/examples/reflection-api/main.cpp
+++ b/examples/reflection-api/main.cpp
@@ -114,6 +114,21 @@ struct ReflectingPrinting
 
         List<ComPtr<slang::IComponentType>> componentsToLink;
 
+        // ### Variable decls
+        //
+        key("global constants");
+        WITH_ARRAY()
+        for (auto decl : module->getModuleReflection()->getChildren())
+        {
+            if (auto varDecl = decl->asVariable(); varDecl &&
+                                                   varDecl->findModifier(slang::Modifier::Const) &&
+                                                   varDecl->findModifier(slang::Modifier::Static))
+            {
+                element();
+                printVariable(varDecl);
+            }
+        }
+
         // ### Finding Entry Points
         //
 
@@ -213,6 +228,13 @@ struct ReflectingPrinting
         printQuotedString(name);
         key("type");
         printType(type);
+
+        int64_t value;
+        if (SLANG_SUCCEEDED(variable->getDefaultValueInt(&value)))
+        {
+            key("value");
+            printf("%" PRId64, value);
+        }
     }
 
     // ### Types
diff --git a/include/slang-deprecated.h b/include/slang-deprecated.h
index 82d81af75..df6e41488 100644
--- a/include/slang-deprecated.h
+++ b/include/slang-deprecated.h
@@ -659,6 +659,8 @@ extern "C"
         SlangSession* globalSession,
         char const* name);
     SLANG_API bool spReflectionVariable_HasDefaultValue(SlangReflectionVariable* inVar);
+    SLANG_API SlangResult
+    spReflectionVariable_GetDefaultValueInt(SlangReflectionVariable* inVar, int64_t* rs);
     SLANG_API SlangReflectionGeneric* spReflectionVariable_GetGenericContainer(
         SlangReflectionVariable* var);
     SLANG_API SlangReflectionVariable* spReflectionVariable_applySpecializations(
diff --git a/include/slang.h b/include/slang.h
index af635e3c4..54647b830 100644
--- a/include/slang.h
+++ b/include/slang.h
@@ -2832,6 +2832,11 @@ struct VariableReflection
         return spReflectionVariable_HasDefaultValue((SlangReflectionVariable*)this);
     }
 
+    SlangResult getDefaultValueInt(int64_t* value)
+    {
+        return spReflectionVariable_GetDefaultValueInt((SlangReflectionVariable*)this, value);
+    }
+
     GenericReflection* getGenericContainer()
     {
         return (GenericReflection*)spReflectionVariable_GetGenericContainer(
diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 0c42817c8..1659a161b 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -1430,7 +1430,7 @@ bool SemanticsVisitor::shouldSkipChecking(Decl* decl, DeclCheckState state)
     return false;
 }
 
-void SemanticsVisitor::_validateCircularVarDefinition(VarDeclBase* varDecl)
+IntVal* SemanticsVisitor::_validateCircularVarDefinition(VarDeclBase* varDecl)
 {
     // The easiest way to test if the declaration is circular is to
     // validate it as a constant.
@@ -1444,8 +1444,11 @@ void SemanticsVisitor::_validateCircularVarDefinition(VarDeclBase* varDecl)
     //
     //
     if (!isScalarIntegerType(varDecl->type))
-        return;
-    tryConstantFoldDeclRef(DeclRef<VarDeclBase>(varDecl), ConstantFoldingKind::LinkTime, nullptr);
+        return nullptr;
+    return tryConstantFoldDeclRef(
+        DeclRef<VarDeclBase>(varDecl),
+        ConstantFoldingKind::LinkTime,
+        nullptr);
 }
 
 void SemanticsDeclModifiersVisitor::visitStructDecl(StructDecl* structDecl)
@@ -2350,7 +2353,13 @@ void SemanticsDeclBodyVisitor::checkVarDeclCommon(VarDeclBase* varDecl)
         // a constant with a circular definition.
         //
         varDecl->setCheckState(DeclCheckState::DefinitionChecked);
-        _validateCircularVarDefinition(varDecl);
+
+        // Update constant value
+        //
+        if (!varDecl->val)
+        {
+            varDecl->val = _validateCircularVarDefinition(varDecl);
+        }
     }
     else
     {
diff --git a/source/slang/slang-check-impl.h b/source/slang/slang-check-impl.h
index edb199299..ba3792af7 100644
--- a/source/slang/slang-check-impl.h
+++ b/source/slang/slang-check-impl.h
@@ -1496,7 +1496,7 @@ public:
     /// by calling a function that indirectly reads the variable) will be allowed and then
     /// exhibit undefined behavior at runtime.
     ///
-    void _validateCircularVarDefinition(VarDeclBase* varDecl);
+    IntVal* _validateCircularVarDefinition(VarDeclBase* varDecl);
 
     bool shouldSkipChecking(Decl* decl, DeclCheckState state);
 
diff --git a/source/slang/slang-reflection-api.cpp b/source/slang/slang-reflection-api.cpp
index 52047a751..9295bfdf6 100644
--- a/source/slang/slang-reflection-api.cpp
+++ b/source/slang/slang-reflection-api.cpp
@@ -3164,6 +3164,22 @@ SLANG_API bool spReflectionVariable_HasDefaultValue(SlangReflectionVariable* inV
     return false;
 }
 
+SLANG_API SlangResult
+spReflectionVariable_GetDefaultValueInt(SlangReflectionVariable* inVar, int64_t* rs)
+{
+    auto decl = convert(inVar).getDecl();
+    if (auto varDecl = as<VarDeclBase>(decl))
+    {
+        if (auto constantVal = as<ConstantIntVal>(varDecl->val))
+        {
+            *rs = constantVal->getValue();
+            return 0;
+        }
+    }
+
+    return SLANG_E_INVALID_ARG;
+}
+
 SLANG_API SlangReflectionGeneric* spReflectionVariable_GetGenericContainer(
     SlangReflectionVariable* var)
 {