Add support for [noinline] attribute (#1650)

This adds the `[noinline]` attribute to the front-end, and passes it through when generating HLSL output.

Notes:

* This change doesn't include a test since the dxc version I have locally parses `[noinline]` but then generates DXIL that fails validation.

* This change doesn't include logic to handle `[noinline]` for other targets. Notably, SPIR-V has decorations that convey the same intention, but we don't yet take advantage of the GLSL extension(s) that would let us generate those decorations.

* By necesstiy, `[noinline]` is only a "strong suggestion" and not actually something the compiler can ever guarantee/enforce.

9 files changed, 53 insertions, 0 deletions

diff --git a/source/slang/core.meta.slang b/source/slang/core.meta.slang
index f8b1bd1f9..9fecc7661 100644
--- a/source/slang/core.meta.slang
+++ b/source/slang/core.meta.slang
@@ -2082,3 +2082,6 @@ attribute_syntax [builtin] : BuiltinAttribute;
 
 __attributeTarget(DeclBase)
 attribute_syntax [__requiresNVAPI] : RequiresNVAPIAttribute;
+
+__attributeTarget(FunctionDeclBase)
+attribute_syntax [noinline] : NoInlineAttribute;
\ No newline at end of file
diff --git a/source/slang/slang-ast-modifier.h b/source/slang/slang-ast-modifier.h
index 55b62483b..3d0c3c6c1 100644
--- a/source/slang/slang-ast-modifier.h
+++ b/source/slang/slang-ast-modifier.h
@@ -937,4 +937,16 @@ class NVAPISlotModifier : public Modifier
     String spaceName;
 };
 
+    /// A `[noinline]` attribute represents a request by the application that,
+    /// to the extent possible, a function should not be inlined into call sites.
+    ///
+    /// Note that due to various limitations of different targets, it is entirely
+    /// possible for such functions to be inlined or specialized to call sites.
+    ///
+class NoInlineAttribute : public Attribute
+{
+    SLANG_AST_CLASS(NoInlineAttribute)
+};
+
+
 } // namespace Slang
diff --git a/source/slang/slang-emit-c-like.cpp b/source/slang/slang-emit-c-like.cpp
index facb8a710..44564e575 100644
--- a/source/slang/slang-emit-c-like.cpp
+++ b/source/slang/slang-emit-c-like.cpp
@@ -3160,6 +3160,7 @@ void CLikeSourceEmitter::emitSimpleFuncImpl(IRFunc* func)
 
     auto name = getName(func);
 
+    emitFuncDecorations(func);
     emitType(resultType, name);
     emitSimpleFuncParamsImpl(func);
     emitSemantics(func);
@@ -3268,6 +3269,7 @@ void CLikeSourceEmitter::emitFuncDecl(IRFunc* func)
 
     auto name = getName(func);
 
+    emitFuncDecorations(func);
     emitType(resultType, name);
 
     m_writer->emit("(");
@@ -3344,6 +3346,15 @@ void CLikeSourceEmitter::emitFunc(IRFunc* func)
     }
 }
 
+void CLikeSourceEmitter::emitFuncDecorations(IRFunc* func)
+{
+    for(auto decoration : func->getDecorations())
+    {
+        emitFuncDecorationImpl(decoration);
+    }
+}
+
+
 void CLikeSourceEmitter::emitStruct(IRStructType* structType)
 {
     // If the selected `struct` type is actually an intrinsic
diff --git a/source/slang/slang-emit-c-like.h b/source/slang/slang-emit-c-like.h
index a26959e54..0544668cc 100644
--- a/source/slang/slang-emit-c-like.h
+++ b/source/slang/slang-emit-c-like.h
@@ -246,6 +246,7 @@ public:
     bool isTargetIntrinsic(IRFunc* func);
 
     void emitFunc(IRFunc* func);
+    void emitFuncDecorations(IRFunc* func);
 
     void emitStruct(IRStructType* structType);
 
@@ -340,6 +341,7 @@ public:
     virtual void emitIntrinsicCallExprImpl(IRCall* inst, IRTargetIntrinsicDecoration* targetIntrinsic, EmitOpInfo const& inOuterPrec);
     virtual void emitFunctionPreambleImpl(IRInst* inst) { SLANG_UNUSED(inst); }
     virtual void emitLoopControlDecorationImpl(IRLoopControlDecoration* decl) { SLANG_UNUSED(decl); }
+    virtual void emitFuncDecorationImpl(IRDecoration* decoration) { SLANG_UNUSED(decoration); }
 
         // Only needed for glsl output with $ prefix intrinsics - so perhaps removable in the future
     virtual void emitTextureOrTextureSamplerTypeImpl(IRTextureTypeBase*  type, char const* baseName) { SLANG_UNUSED(type); SLANG_UNUSED(baseName); }
diff --git a/source/slang/slang-emit-hlsl.cpp b/source/slang/slang-emit-hlsl.cpp
index 57d603940..a1da1bbdf 100644
--- a/source/slang/slang-emit-hlsl.cpp
+++ b/source/slang/slang-emit-hlsl.cpp
@@ -693,6 +693,20 @@ void HLSLSourceEmitter::emitLoopControlDecorationImpl(IRLoopControlDecoration* d
     }
 }
 
+void HLSLSourceEmitter::emitFuncDecorationImpl(IRDecoration* decoration)
+{
+    switch( decoration->op )
+    {
+    case kIROp_NoInlineDecoration:
+        m_writer->emit("[noinline]\n");
+        break;
+
+    default:
+        break;
+    }
+}
+
+
 void HLSLSourceEmitter::emitSimpleValueImpl(IRInst* inst)
 {
     switch (inst->op)
diff --git a/source/slang/slang-emit-hlsl.h b/source/slang/slang-emit-hlsl.h
index b93cc694b..614ee58bc 100644
--- a/source/slang/slang-emit-hlsl.h
+++ b/source/slang/slang-emit-hlsl.h
@@ -45,6 +45,8 @@ protected:
     virtual bool tryEmitInstExprImpl(IRInst* inst, const EmitOpInfo& inOuterPrec) SLANG_OVERRIDE;
     virtual void emitSimpleValueImpl(IRInst* inst) SLANG_OVERRIDE;
     virtual void emitLoopControlDecorationImpl(IRLoopControlDecoration* decl) SLANG_OVERRIDE;
+    virtual void emitFuncDecorationImpl(IRDecoration* decoration) SLANG_OVERRIDE;
+
 
     virtual void handleRequiredCapabilitiesImpl(IRInst* inst) SLANG_OVERRIDE;
     virtual void emitPreludeDirectivesImpl() SLANG_OVERRIDE;
diff --git a/source/slang/slang-ir-inst-defs.h b/source/slang/slang-ir-inst-defs.h
index 736cb0cec..7b26ad9cb 100644
--- a/source/slang/slang-ir-inst-defs.h
+++ b/source/slang/slang-ir-inst-defs.h
@@ -599,6 +599,9 @@ INST(HighLevelDeclDecoration,               highLevelDecl,          1, 0)
         /// that the NVAPI shader parameter intends to use.
     INST(NVAPISlotDecoration, nvapiSlot, 2, 0)
 
+        /// Applie to an IR function and signals that inlining should not be performed unless unavoidable.
+    INST(NoInlineDecoration, noInline, 0, 0)
+
     INST(SemanticDecoration, semantic, 2, 0)
 
     INST_RANGE(Decoration, HighLevelDeclDecoration, SemanticDecoration)
diff --git a/source/slang/slang-ir-insts.h b/source/slang/slang-ir-insts.h
index dc42fde70..3c7406d3b 100644
--- a/source/slang/slang-ir-insts.h
+++ b/source/slang/slang-ir-insts.h
@@ -266,6 +266,7 @@ IR_SIMPLE_DECORATION(PreciseDecoration)
 IR_SIMPLE_DECORATION(PublicDecoration)
 IR_SIMPLE_DECORATION(KeepAliveDecoration)
 IR_SIMPLE_DECORATION(RequiresNVAPIDecoration)
+IR_SIMPLE_DECORATION(NoInlineDecoration)
 
 struct IRNVAPIMagicDecoration : IRDecoration
 {
diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index 34b189b14..1ea3c71fb 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -7041,6 +7041,11 @@ struct DeclLoweringVisitor : DeclVisitor<DeclLoweringVisitor, LoweredValInfo>
             getBuilder()->addSimpleDecoration<IRRequiresNVAPIDecoration>(irFunc);
         }
 
+        if(decl->findModifier<NoInlineAttribute>())
+        {
+            getBuilder()->addSimpleDecoration<IRNoInlineDecoration>(irFunc);
+        }
+
         if (decl->findModifier<PublicModifier>()) {
             getBuilder()->addSimpleDecoration<IRPublicDecoration>(irFunc);
         }