compiler: implement internal/abi.Escape

Author: aykevl

compiler/intrinsics.go

@@ -121,6 +121,29 @@ func (b *builder) createKeepAliveImpl() {
 	b.CreateRetVoid()
 }
 
+// createAbiEscapeImpl implements the generic internal/abi.Escape function. It
+// currently only supports pointer types.
+func (b *builder) createAbiEscapeImpl() {
+	b.createFunctionStart(true)
+
+	// The first parameter is assumed to be a pointer. This is checked at the
+	// call site of createAbiEscapeImpl.
+	pointerValue := b.getValue(b.fn.Params[0], getPos(b.fn))
+
+	// Create an equivalent of the following C code, which is basically just a
+	// nop but ensures the pointerValue is kept alive:
+	//
+	//     __asm__ __volatile__("" : : "r"(pointerValue))
+	//
+	// It should be portable to basically everything as the "r" register type
+	// exists basically everywhere.
+	asmType := llvm.FunctionType(b.dataPtrType, []llvm.Type{b.dataPtrType}, false)
+	asmFn := llvm.InlineAsm(asmType, "", "=r,0", true, false, 0, false)
+	result := b.createCall(asmType, asmFn, []llvm.Value{pointerValue}, "")
+
+	b.CreateRet(result)
+}
+
 var mathToLLVMMapping = map[string]string{
 	"math.Ceil":  "llvm.ceil.f64",
 	"math.Exp":   "llvm.exp.f64",

compiler/symbol.go

@@ -253,6 +253,23 @@ func (c *compilerContext) maybeCreateSyntheticFunction(fn *ssa.Function, llvmFn
 	// The exception is the package initializer, which does appear in the
 	// *ssa.Package members and so shouldn't be created here.
 	if fn.Synthetic != "" && fn.Synthetic != "package initializer" && fn.Synthetic != "generic function" && fn.Synthetic != "range-over-func yield" {
+		if origin := fn.Origin(); origin != nil && origin.RelString(nil) == "internal/abi.Escape" {
+			// This is a special implementation or internal/abi.Escape, which
+			// can only really be implemented in the compiler.
+			// For simplicity we'll only implement pointer parameters for now.
+			if _, ok := fn.Params[0].Type().Underlying().(*types.Pointer); ok {
+				irbuilder := c.ctx.NewBuilder()
+				defer irbuilder.Dispose()
+				b := newBuilder(c, irbuilder, fn)
+				b.createAbiEscapeImpl()
+				llvmFn.SetLinkage(llvm.LinkOnceODRLinkage)
+				llvmFn.SetUnnamedAddr(true)
+			}
+			// If the parameter is not of a pointer type, it will be left
+			// unimplemented. This will result in a linker error if the function
+			// is really called, making it clear it needs to be implemented.
+			return
+		}
 		if len(fn.Blocks) == 0 {
 			c.addError(fn.Pos(), "missing function body")
 			return

src/internal/abi/escape.go

@@ -8,3 +8,10 @@ import "unsafe"
 func NoEscape(p unsafe.Pointer) unsafe.Pointer {
 	return p
 }
+
+func Escape[T any](x T) T {
+	// This function is either implemented in the compiler, or left undefined
+	// for some variation of T. The body of this function should not be compiled
+	// as-is.
+	panic("internal/abi.Escape: unreachable (implemented in the compiler)")
+}