tint: Stub intrinsic @const evaluation

Add support for @const to builtins in intrinsics.def.
Propagate this flag through to the intrinsic table.
Handle builtins that are @const annotated in the resolver.

Currently no intrinsics are decorated with @const, so there's nothing to
test (yet).

Bug: tint:1504
Change-Id: I172483688617782bd7c58b70e3f38d0222a5d1af
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/92323
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>

tools/src/cmd/intrinsic-gen/gen/builtin_table.go

@@ -105,6 +105,8 @@ type Overload struct {
 	IsDeprecated bool
 	// The kind of overload
 	Kind string
+	// The function name used to evaluate the overload at shader-creation time
+	ConstEvalFunction string
 }
 
 // Intrinsic is used to create the C++ IntrinsicInfo structure
@@ -206,6 +208,7 @@ func (b *IntrinsicTableBuilder) buildOverload(o *sem.Overload) (Overload, error)
 		CanBeUsedInStage:           o.CanBeUsedInStage,
 		IsDeprecated:               o.IsDeprecated,
 		Kind:                       string(o.Decl.Kind),
+		ConstEvalFunction:          o.ConstEvalFunction,
 	}, nil
 }
 

tools/src/cmd/intrinsic-gen/resolver/resolve.go

@@ -326,6 +326,16 @@ func (r *resolver) intrinsic(
 			Compute:  true,
 		}
 	}
+	if constEvalFn := a.Attributes.Take("const"); constEvalFn != nil {
+		switch len(constEvalFn.Values) {
+		case 0:
+			overload.ConstEvalFunction = overload.Decl.Name
+		case 1:
+			overload.ConstEvalFunction = constEvalFn.Values[0]
+		default:
+			return fmt.Errorf("%v too many values for @const attribute", constEvalFn.Source)
+		}
+	}
 	if deprecated := a.Attributes.Take("deprecated"); deprecated != nil {
 		overload.IsDeprecated = true
 		if len(deprecated.Values) != 0 {

tools/src/cmd/intrinsic-gen/sem/sem.go

@@ -143,15 +143,16 @@ type Intrinsic struct {
 
 // Overload describes a single overload of a builtin or operator
 type Overload struct {
-	Decl             ast.IntrinsicDecl
-	Intrinsic        *Intrinsic
-	TemplateParams   []TemplateParam
-	TemplateTypes    []*TemplateTypeParam
-	TemplateNumbers  []TemplateParam
-	ReturnType       *FullyQualifiedName
-	Parameters       []Parameter
-	CanBeUsedInStage StageUses
-	IsDeprecated     bool // True if this overload is deprecated
+	Decl              ast.IntrinsicDecl
+	Intrinsic         *Intrinsic
+	TemplateParams    []TemplateParam
+	TemplateTypes     []*TemplateTypeParam
+	TemplateNumbers   []TemplateParam
+	ReturnType        *FullyQualifiedName
+	Parameters        []Parameter
+	CanBeUsedInStage  StageUses
+	IsDeprecated      bool   // True if this overload is deprecated
+	ConstEvalFunction string // Name of the function used to evaluate the intrinsic at shader creation time
 }
 
 // StageUses describes the stages an overload can be used in