re PR go/91781 (r275691 breaks go test "reflect")

PR go/91781
    reflect: promote integer closure return to full word
    
    The libffi library expects an integer return type to be promoted to a
    full word.  Implement that when returning from a closure written in Go.
    This only matters on big-endian systems when returning an integer smaller
    than the pointer size, which is why we didn't notice it until now.
    
    Fixes https://gcc.gnu.org/PR91781.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/195858

From-SVN: r275813

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-ff18e041624b8c23ffcd747f51e9dda945777d2a
+7aabaf8623cf88e2378057476a034093abbe5aab
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/reflect/makefunc_ffi.go

@@ -28,7 +28,7 @@ func makeCIF(ft *funcType) unsafe.Pointer
 //
 // The ffi_callback handles __go_makefunc_can_recover, and
 // then passes off the data as received from ffi here.
-func ffiCallbackGo(results unsafe.Pointer, params unsafe.Pointer, impl *makeFuncImpl) {
+func ffiCallbackGo(results unsafe.Pointer, params unsafe.Pointer, impl *makeFuncImpl, wordsize int32, bigEndian bool) {
 	ftyp := impl.typ
 	in := make([]Value, 0, len(ftyp.in))
 	ap := params
@@ -42,21 +42,46 @@ func ffiCallbackGo(results unsafe.Pointer, params unsafe.Pointer, impl *makeFunc
 
 	out := impl.call(in)
 
-	off := uintptr(0)
+	checkValue := func(v Value, typ *rtype, addr unsafe.Pointer) {
-	for i, typ := range ftyp.out {
-		v := out[i]
 		if v.flag&flagRO != 0 {
 			panic("reflect: function created by MakeFunc using " + funcName(impl.fn) +
 				" returned value obtained from unexported field")
 		}
 
-		off = align(off, uintptr(typ.fieldAlign))
-		addr := unsafe.Pointer(uintptr(results) + off)
-
 		// Convert v to type typ if v is assignable to a variable
 		// of type t in the language spec.
 		// See issue 28761.
 		v = v.assignTo("reflect.MakeFunc", typ, addr)
+	}
+
+	// In libffi a single integer return value is always promoted
+	// to a full word. This only matters for integers whose size
+	// is less than the size of a full word. There is similar code
+	// in libgo/runtime/go-reflect-call.c.
+	if len(ftyp.out) == 1 {
+		typ := ftyp.out[0]
+		switch typ.Kind() {
+		case Bool, Int8, Int16, Int32, Uint8, Uint16, Uint32:
+			v := out[0]
+			checkValue(v, typ, nil)
+
+			if bigEndian {
+				results = unsafe.Pointer(uintptr(results) + uintptr(wordsize) - typ.size)
+			}
+
+			memmove(results, v.ptr, typ.size)
+			return
+		}
+	}
+
+	off := uintptr(0)
+	for i, typ := range ftyp.out {
+		v := out[i]
+
+		off = align(off, uintptr(typ.fieldAlign))
+		addr := unsafe.Pointer(uintptr(results) + off)
+
+		checkValue(v, typ, addr)
 
 		if v.flag&flagIndir == 0 && (v.kind() == Ptr || v.kind() == UnsafePointer) {
 			*(*unsafe.Pointer)(addr) = v.ptr

libgo/go/reflect/makefunc_ffi_c.c

@@ -25,7 +25,8 @@ void makeFuncFFI(void *cif, void *impl)
    function ffiCall with the pointer to the arguments, the results area,
    and the closure structure.  */
 
-extern void ffiCallbackGo(void *result, void **args, ffi_go_closure *closure)
+extern void ffiCallbackGo(void *result, void **args, ffi_go_closure *closure,
+                          int32 wordsize, _Bool big_endian)
   __asm__ (GOSYM_PREFIX "reflect.ffiCallbackGo");
 
 extern void makefuncfficanrecover(Slice)
@@ -72,7 +73,8 @@ ffi_callback (ffi_cif* cif __attribute__ ((unused)), void *results,
       makefuncfficanrecover (s);
     }
 
-  ffiCallbackGo(results, args, closure);
+  ffiCallbackGo(results, args, closure, sizeof(ffi_arg),
+                __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__);
 
   if (i < n)
     makefuncreturning ();

libgo/runtime/go-reflect-call.c

@@ -44,8 +44,8 @@ go_results_size (const struct functype *func)
 
   types = (const struct _type **) func->out.__values;
 
-  /* A single integer return value is always promoted to a full
+  /* A single integer return value is always promoted to a full word.
-     word.  */
+     There is similar code below and in libgo/go/reflect/makefunc_ffi.go.*/
   if (count == 1)
     {
       switch (types[0]->kind & kindMask)
@@ -57,8 +57,6 @@ go_results_size (const struct functype *func)
 	case kindUint8:
 	case kindUint16:
 	case kindUint32:
-	case kindInt:
-	case kindUint:
 	  return sizeof (ffi_arg);
 
 	default:
@@ -108,8 +106,8 @@ go_set_results (const struct functype *func, unsigned char *call_result,
 
   types = (const struct _type **) func->out.__values;
 
-  /* A single integer return value is always promoted to a full
+  /* A single integer return value is always promoted to a full word.
-     word.  */
+     There is similar code above and in libgo/go/reflect/makefunc_ffi.go.*/
   if (count == 1)
     {
       switch (types[0]->kind & kindMask)
@@ -121,8 +119,6 @@ go_set_results (const struct functype *func, unsigned char *call_result,
 	case kindUint8:
 	case kindUint16:
 	case kindUint32:
-	case kindInt:
-	case kindUint:
 	  {
 	    union
 	    {