compiler: support function pointers outside of addrspace 0

In LLVM 8, the AVR backend has moved all function pointers to address
space 1 by default. Much of the code still assumes function pointers
live in address space 0, leading to assertion failures.

This commit fixes this problem by autodetecting function pointers and
avoiding them in interface pseudo-calls.

4 files changed, 29 insertions, 23 deletions

diff --git a/compiler/compiler.go b/compiler/compiler.go
index a60341af1..26f145b5d 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -57,6 +57,7 @@ type Compiler struct {
 	targetData              llvm.TargetData
 	intType                 llvm.Type
 	i8ptrType               llvm.Type // for convenience
+	funcPtrAddrSpace        int
 	uintptrType             llvm.Type
 	initFuncs               []llvm.Value
 	interfaceInvokeWrappers []interfaceInvokeWrapper
@@ -125,6 +126,11 @@ func NewCompiler(pkgName string, config Config) (*Compiler, error) {
 	}
 	c.i8ptrType = llvm.PointerType(c.ctx.Int8Type(), 0)
 
+	dummyFuncType := llvm.FunctionType(c.ctx.VoidType(), nil, false)
+	dummyFunc := llvm.AddFunction(c.mod, "tinygo.dummy", dummyFuncType)
+	c.funcPtrAddrSpace = dummyFunc.Type().PointerAddressSpace()
+	dummyFunc.EraseFromParentAsFunction()
+
 	return c, nil
 }
 
@@ -462,7 +468,7 @@ func (c *Compiler) getLLVMType(goType types.Type) (llvm.Type, error) {
 		// {context, funcptr}
 		paramTypes = append(paramTypes, c.i8ptrType) // context
 		paramTypes = append(paramTypes, c.i8ptrType) // parent coroutine
-		ptr := llvm.PointerType(llvm.FunctionType(returnType, paramTypes, false), 0)
+		ptr := llvm.PointerType(llvm.FunctionType(returnType, paramTypes, false), c.funcPtrAddrSpace)
 		ptr = c.ctx.StructType([]llvm.Type{c.i8ptrType, ptr}, false)
 		return ptr, nil
 	case *types.Slice:
diff --git a/compiler/interface-lowering.go b/compiler/interface-lowering.go
index 520932334..736237093 100644
--- a/compiler/interface-lowering.go
+++ b/compiler/interface-lowering.go
@@ -304,7 +304,7 @@ func (p *lowerInterfacesPass) run() {
 			// interface value should already have returned false.
 			// Replace the function pointer with undef (which will then be
 			// called), indicating to the optimizer this code is unreachable.
-			use.ReplaceAllUsesWith(llvm.Undef(p.i8ptrType))
+			use.ReplaceAllUsesWith(llvm.Undef(p.uintptrType))
 			use.EraseFromParentAsInstruction()
 		} else if len(itf.types) == 1 {
 			// There is only one implementation of the given type.
@@ -314,12 +314,12 @@ func (p *lowerInterfacesPass) run() {
 			// There are multiple types implementing this interface, thus there
 			// are multiple possible functions to call. Delegate calling the
 			// right function to a special wrapper function.
-			bitcasts := getUses(use)
-			if len(bitcasts) != 1 || bitcasts[0].IsABitCastInst().IsNil() {
-				panic("expected exactly one bitcast use of runtime.interfaceMethod")
+			inttoptrs := getUses(use)
+			if len(inttoptrs) != 1 || inttoptrs[0].IsAIntToPtrInst().IsNil() {
+				panic("expected exactly one inttoptr use of runtime.interfaceMethod")
 			}
-			bitcast := bitcasts[0]
-			calls := getUses(bitcast)
+			inttoptr := inttoptrs[0]
+			calls := getUses(inttoptr)
 			if len(calls) != 1 || calls[0].IsACallInst().IsNil() {
 				panic("expected exactly one call use of runtime.interfaceMethod")
 			}
@@ -340,14 +340,14 @@ func (p *lowerInterfacesPass) run() {
 			// call, after selecting the right concrete type.
 			redirector := p.getInterfaceMethodFunc(itf, signature, call.Type(), paramTypes)
 
-			// Replace the old lookup/bitcast/call with the new call.
+			// Replace the old lookup/inttoptr/call with the new call.
 			p.builder.SetInsertPointBefore(call)
 			retval := p.builder.CreateCall(redirector, params, "")
 			if retval.Type().TypeKind() != llvm.VoidTypeKind {
 				call.ReplaceAllUsesWith(retval)
 			}
 			call.EraseFromParentAsInstruction()
-			bitcast.EraseFromParentAsInstruction()
+			inttoptr.EraseFromParentAsInstruction()
 			use.EraseFromParentAsInstruction()
 		}
 	}
@@ -542,22 +542,22 @@ func (p *lowerInterfacesPass) getSignature(name string) *signatureInfo {
 	return p.signatures[name]
 }
 
-// replaceInvokeWithCall replaces a runtime.interfaceMethod + bitcast with a
+// replaceInvokeWithCall replaces a runtime.interfaceMethod + inttoptr with a
 // concrete method. This can be done when only one type implements the
 // interface.
 func (p *lowerInterfacesPass) replaceInvokeWithCall(use llvm.Value, typ *typeInfo, signature *signatureInfo) {
-	bitcasts := getUses(use)
-	if len(bitcasts) != 1 || bitcasts[0].IsABitCastInst().IsNil() {
-		panic("expected exactly one bitcast use of runtime.interfaceMethod")
+	inttoptrs := getUses(use)
+	if len(inttoptrs) != 1 || inttoptrs[0].IsAIntToPtrInst().IsNil() {
+		panic("expected exactly one inttoptr use of runtime.interfaceMethod")
 	}
-	bitcast := bitcasts[0]
+	inttoptr := inttoptrs[0]
 	function := typ.getMethod(signature).function
-	if bitcast.Type() != function.Type() {
+	if inttoptr.Type() != function.Type() {
 		p.builder.SetInsertPointBefore(use)
-		function = p.builder.CreateBitCast(function, bitcast.Type(), "")
+		function = p.builder.CreateBitCast(function, inttoptr.Type(), "")
 	}
-	bitcast.ReplaceAllUsesWith(function)
-	bitcast.EraseFromParentAsInstruction()
+	inttoptr.ReplaceAllUsesWith(function)
+	inttoptr.EraseFromParentAsInstruction()
 	use.EraseFromParentAsInstruction()
 }
 
diff --git a/compiler/interface.go b/compiler/interface.go
index 3a2f64bfe..f39bc1059 100644
--- a/compiler/interface.go
+++ b/compiler/interface.go
@@ -203,7 +203,7 @@ func (c *Compiler) getTypeMethodSet(typ types.Type) (llvm.Value, error) {
 		}
 		methodInfo := llvm.ConstNamedStruct(interfaceMethodInfoType, []llvm.Value{
 			signatureGlobal,
-			llvm.ConstBitCast(fn, c.i8ptrType),
+			llvm.ConstPtrToInt(fn, c.uintptrType),
 		})
 		methods[i] = methodInfo
 	}
@@ -400,7 +400,7 @@ func (c *Compiler) getInvokeCall(frame *Frame, instr *ssa.CallCommon) (llvm.Valu
 		c.getMethodSignature(instr.Method),
 	}
 	fn := c.createRuntimeCall("interfaceMethod", values, "invoke.func")
-	fnCast := c.builder.CreateBitCast(fn, llvmFnType, "invoke.func.cast")
+	fnCast := c.builder.CreateIntToPtr(fn, llvmFnType, "invoke.func.cast")
 	receiverValue := c.builder.CreateExtractValue(itf, 1, "invoke.func.receiver")
 
 	args := []llvm.Value{receiverValue}
diff --git a/src/runtime/interface.go b/src/runtime/interface.go
index 3daf56d23..61d3114da 100644
--- a/src/runtime/interface.go
+++ b/src/runtime/interface.go
@@ -39,8 +39,8 @@ func interfaceTypeAssert(ok bool) {
 // See compiler/interface-lowering.go for details.
 
 type interfaceMethodInfo struct {
-	signature *uint8 // external *i8 with a name identifying the Go function signature
-	funcptr   *uint8 // bitcast from the actual function pointer
+	signature *uint8  // external *i8 with a name identifying the Go function signature
+	funcptr   uintptr // bitcast from the actual function pointer
 }
 
 // Pseudo function call used while putting a concrete value in an interface,
@@ -59,4 +59,4 @@ func interfaceImplements(typecode uintptr, interfaceMethodSet **uint8) bool
 
 // Pseudo function that returns a function pointer to the method to call.
 // See the interface lowering pass for how this is lowered to a real call.
-func interfaceMethod(typecode uintptr, interfaceMethodSet **uint8, signature *uint8) *uint8
+func interfaceMethod(typecode uintptr, interfaceMethodSet **uint8, signature *uint8) uintptr