compiler: decouple func lowering from interface type codes

There is no good reason for func values to refer to interface type
codes. The only thing they need is a stable identifier for function
signatures, which is easily created as a new kind of globals. Decoupling
makes it easier to change interface related code.

compiler/compiler.go

@@ -23,7 +23,7 @@ import (
 // Version of the compiler pacakge. Must be incremented each time the compiler
 // package changes in a way that affects the generated LLVM module.
 // This version is independent of the TinyGo version number.
-const Version = 7 // last change: don't rely on runtime.typecodeID struct type name
+const Version = 8 // last change: don't use runtime.typecodeID in func lowering
 
 func init() {
 	llvm.InitializeAllTargets()

compiler/func.go

@@ -25,14 +25,13 @@ func (c *compilerContext) createFuncValue(builder llvm.Builder, funcPtr, context
 		// Closure is: {context, function pointer}
 		funcValueScalar = funcPtr
 	case "switch":
-		sigGlobal := c.getTypeCode(sig)
 		funcValueWithSignatureGlobalName := funcPtr.Name() + "$withSignature"
 		funcValueWithSignatureGlobal := c.mod.NamedGlobal(funcValueWithSignatureGlobalName)
 		if funcValueWithSignatureGlobal.IsNil() {
 			funcValueWithSignatureType := c.getLLVMRuntimeType("funcValueWithSignature")
 			funcValueWithSignature := llvm.ConstNamedStruct(funcValueWithSignatureType, []llvm.Value{
 				llvm.ConstPtrToInt(funcPtr, c.uintptrType),
-				sigGlobal,
+				c.getFuncSignatureID(sig),
 			})
 			funcValueWithSignatureGlobal = llvm.AddGlobal(c.mod, funcValueWithSignatureType, funcValueWithSignatureGlobalName)
 			funcValueWithSignatureGlobal.SetInitializer(funcValueWithSignature)
@@ -50,6 +49,19 @@ func (c *compilerContext) createFuncValue(builder llvm.Builder, funcPtr, context
 	return funcValue
 }
 
+// getFuncSignatureID returns a new external global for a given signature. This
+// global reference is not real, it is only used during func lowering to assign
+// signature types to functions and will then be removed.
+func (c *compilerContext) getFuncSignatureID(sig *types.Signature) llvm.Value {
+	sigGlobalName := "reflect/types.funcid:" + getTypeCodeName(sig)
+	sigGlobal := c.mod.NamedGlobal(sigGlobalName)
+	if sigGlobal.IsNil() {
+		sigGlobal = llvm.AddGlobal(c.mod, c.ctx.Int8Type(), sigGlobalName)
+		sigGlobal.SetGlobalConstant(true)
+	}
+	return sigGlobal
+}
+
 // extractFuncScalar returns some scalar that can be used in comparisons. It is
 // a cheap operation.
 func (b *builder) extractFuncScalar(funcValue llvm.Value) llvm.Value {
@@ -71,7 +83,7 @@ func (b *builder) decodeFuncValue(funcValue llvm.Value, sig *types.Signature) (f
 		funcPtr = b.CreateExtractValue(funcValue, 1, "")
 	case "switch":
 		llvmSig := b.getRawFuncType(sig)
-		sigGlobal := b.getTypeCode(sig)
+		sigGlobal := b.getFuncSignatureID(sig)
 		funcPtr = b.createRuntimeCall("getFuncPtr", []llvm.Value{funcValue, sigGlobal}, "")
 		funcPtr = b.CreateIntToPtr(funcPtr, llvmSig, "")
 	default:

compiler/testdata/func.ll

@@ -3,12 +3,10 @@ source_filename = "func.go"
 target datalayout = "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-f64:32:64-f80:32-n8:16:32-S128"
 target triple = "i686--linux"
 
-%runtime.typecodeID = type { %runtime.typecodeID*, i32, %runtime.interfaceMethodInfo* }
-%runtime.interfaceMethodInfo = type { i8*, i32 }
-%runtime.funcValueWithSignature = type { i32, %runtime.typecodeID* }
+%runtime.funcValueWithSignature = type { i32, i8* }
 
-@"reflect/types.type:func:{basic:int}{}" = linkonce_odr constant %runtime.typecodeID zeroinitializer
-@"main.someFunc$withSignature" = linkonce_odr constant %runtime.funcValueWithSignature { i32 ptrtoint (void (i32, i8*, i8*)* @main.someFunc to i32), %runtime.typecodeID* @"reflect/types.type:func:{basic:int}{}" }
+@"reflect/types.funcid:func:{basic:int}{}" = external constant i8
+@"main.someFunc$withSignature" = linkonce_odr constant %runtime.funcValueWithSignature { i32 ptrtoint (void (i32, i8*, i8*)* @main.someFunc to i32), i8* @"reflect/types.funcid:func:{basic:int}{}" }
 
 declare noalias nonnull i8* @runtime.alloc(i32, i8*, i8*)
 
@@ -19,7 +17,7 @@ entry:
 
 define hidden void @main.foo(i8* %callback.context, i32 %callback.funcptr, i8* %context, i8* %parentHandle) unnamed_addr {
 entry:
-  %0 = call i32 @runtime.getFuncPtr(i8* %callback.context, i32 %callback.funcptr, %runtime.typecodeID* nonnull @"reflect/types.type:func:{basic:int}{}", i8* undef, i8* null)
+  %0 = call i32 @runtime.getFuncPtr(i8* %callback.context, i32 %callback.funcptr, i8* nonnull @"reflect/types.funcid:func:{basic:int}{}", i8* undef, i8* null)
   %1 = icmp eq i32 %0, 0
   br i1 %1, label %fpcall.throw, label %fpcall.next
 
@@ -33,7 +31,7 @@ fpcall.next:                                      ; preds = %entry
   ret void
 }
 
-declare i32 @runtime.getFuncPtr(i8*, i32, %runtime.typecodeID* dereferenceable_or_null(12), i8*, i8*)
+declare i32 @runtime.getFuncPtr(i8*, i32, i8* dereferenceable_or_null(1), i8*, i8*)
 
 declare void @runtime.nilPanic(i8*, i8*)