compiler: really define runtime.mem* as LLVM intrinsic wrappers

This makes it possible to //go:linkname them from other places, like in
the reflect package. And is in my opinion a much cleaner solution.

compiler/compiler.go

@@ -1619,10 +1619,6 @@ func (b *builder) createFunctionCall(instr *ssa.CallCommon) (llvm.Value, error)
 		// applied) function call. If it is anonymous, it may be a closure.
 		name := fn.RelString(nil)
 		switch {
-		case name == "runtime.memcpy" || name == "runtime.memmove" || name == "reflect.memcpy":
-			return b.createMemoryCopyCall(fn, instr.Args)
-		case name == "runtime.memzero":
-			return b.createMemoryZeroCall(instr.Args)
 		case name == "math.Ceil" || name == "math.Floor" || name == "math.Sqrt" || name == "math.Trunc":
 			result, ok := b.createMathOp(instr)
 			if ok {

compiler/intrinsics.go

@@ -20,6 +20,10 @@ import (
 func (b *builder) defineIntrinsicFunction() {
 	name := b.fn.RelString(nil)
 	switch {
+	case name == "runtime.memcpy" || name == "runtime.memmove":
+		b.createMemoryCopyImpl()
+	case name == "runtime.memzero":
+		b.createMemoryZeroImpl()
 	case strings.HasPrefix(name, "runtime/volatile.Load"):
 		b.createVolatileLoad()
 	case strings.HasPrefix(name, "runtime/volatile.Store"):
@@ -35,30 +39,32 @@ func (b *builder) defineIntrinsicFunction() {
 	}
 }
 
-// createMemoryCopyCall creates a call to a builtin LLVM memcpy or memmove
+// createMemoryCopyImpl creates a call to a builtin LLVM memcpy or memmove
 // function, declaring this function if needed. These calls are treated
 // specially by optimization passes possibly resulting in better generated code,
 // and will otherwise be lowered to regular libc memcpy/memmove calls.
-func (b *builder) createMemoryCopyCall(fn *ssa.Function, args []ssa.Value) (llvm.Value, error) {
-	fnName := "llvm." + fn.Name() + ".p0i8.p0i8.i" + strconv.Itoa(b.uintptrType.IntTypeWidth())
+func (b *builder) createMemoryCopyImpl() {
+	b.createFunctionStart()
+	fnName := "llvm." + b.fn.Name() + ".p0i8.p0i8.i" + strconv.Itoa(b.uintptrType.IntTypeWidth())
 	llvmFn := b.mod.NamedFunction(fnName)
 	if llvmFn.IsNil() {
 		fnType := llvm.FunctionType(b.ctx.VoidType(), []llvm.Type{b.i8ptrType, b.i8ptrType, b.uintptrType, b.ctx.Int1Type()}, false)
 		llvmFn = llvm.AddFunction(b.mod, fnName, fnType)
 	}
 	var params []llvm.Value
-	for _, param := range args {
+	for _, param := range b.fn.Params {
 		params = append(params, b.getValue(param))
 	}
 	params = append(params, llvm.ConstInt(b.ctx.Int1Type(), 0, false))
 	b.CreateCall(llvmFn, params, "")
-	return llvm.Value{}, nil
+	b.CreateRetVoid()
 }
 
-// createMemoryZeroCall creates calls to llvm.memset.* to zero a block of
+// createMemoryZeroImpl creates calls to llvm.memset.* to zero a block of
 // memory, declaring the function if needed. These calls will be lowered to
 // regular libc memset calls if they aren't optimized out in a different way.
-func (b *builder) createMemoryZeroCall(args []ssa.Value) (llvm.Value, error) {
+func (b *builder) createMemoryZeroImpl() {
+	b.createFunctionStart()
 	fnName := "llvm.memset.p0i8.i" + strconv.Itoa(b.uintptrType.IntTypeWidth())
 	llvmFn := b.mod.NamedFunction(fnName)
 	if llvmFn.IsNil() {
@@ -66,13 +72,13 @@ func (b *builder) createMemoryZeroCall(args []ssa.Value) (llvm.Value, error) {
 		llvmFn = llvm.AddFunction(b.mod, fnName, fnType)
 	}
 	params := []llvm.Value{
-		b.getValue(args[0]),
+		b.getValue(b.fn.Params[0]),
 		llvm.ConstInt(b.ctx.Int8Type(), 0, false),
-		b.getValue(args[1]),
+		b.getValue(b.fn.Params[1]),
 		llvm.ConstInt(b.ctx.Int1Type(), 0, false),
 	}
 	b.CreateCall(llvmFn, params, "")
-	return llvm.Value{}, nil
+	b.CreateRetVoid()
 }
 
 var mathToLLVMMapping = map[string]string{

src/reflect/value.go

@@ -808,8 +808,7 @@ func (e *ValueError) Error() string {
 	return "reflect: call of " + e.Method + " on " + e.Kind.String() + " Value"
 }
 
-// Calls to this function are converted to LLVM intrinsic calls such as
-// llvm.memcpy.p0i8.p0i8.i32().
+//go:linkname memcpy runtime.memcpy
 func memcpy(dst, src unsafe.Pointer, size uintptr)
 
 //go:linkname alloc runtime.alloc

src/runtime/runtime.go

@@ -26,19 +26,19 @@ func GOROOT() string {
 }
 
 // Copy size bytes from src to dst. The memory areas must not overlap.
-// Calls to this function are converted to LLVM intrinsic calls such as
-// llvm.memcpy.p0i8.p0i8.i32(dst, src, size, false).
+// This function is implemented by the compiler as a call to a LLVM intrinsic
+// like llvm.memcpy.p0i8.p0i8.i32(dst, src, size, false).
 func memcpy(dst, src unsafe.Pointer, size uintptr)
 
 // Copy size bytes from src to dst. The memory areas may overlap and will do the
 // correct thing.
-// Calls to this function are converted to LLVM intrinsic calls such as
-// llvm.memmove.p0i8.p0i8.i32(dst, src, size, false).
+// This function is implemented by the compiler as a call to a LLVM intrinsic
+// like llvm.memmove.p0i8.p0i8.i32(dst, src, size, false).
 func memmove(dst, src unsafe.Pointer, size uintptr)
 
 // Set the given number of bytes to zero.
-// Calls to this function are converted to LLVM intrinsic calls such as
-// llvm.memset.p0i8.i32(ptr, 0, size, false).
+// This function is implemented by the compiler as a call to a LLVM intrinsic
+// like llvm.memset.p0i8.i32(ptr, 0, size, false).
 func memzero(ptr unsafe.Pointer, size uintptr)
 
 // This intrinsic returns the current stack pointer.