compile, runtime: make selectnbrecv return two values

The only different between selectnbrecv and selectnbrecv2 is the later
set the input pointer value by second return value from chanrecv.

So by making selectnbrecv return two values from chanrecv, we can get
rid of selectnbrecv2, the compiler can now call only selectnbrecv and
generate simpler code.

This is the gofrontend version of https://golang.org/cl/292890.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/339529

4 files changed, 37 insertions, 63 deletions

diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 801e039..5a097ff 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-54361805bd611d896042b879ee7f6d2d4d088537
+2031f0be9c0b5fda6421d290a0261eb6bd1c8205
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/gcc/go/gofrontend/runtime.def b/gcc/go/gofrontend/runtime.def
index fad8ceb..87a2708 100644
--- a/gcc/go/gofrontend/runtime.def
+++ b/gcc/go/gofrontend/runtime.def
@@ -204,12 +204,8 @@ DEF_GO_RUNTIME(SELECTNBSEND, "runtime.selectnbsend", P2(CHAN, POINTER), R1(BOOL)
 
 // Non-blocking receive a value from a channel, used for two-case select
 // statement with a default case.
-DEF_GO_RUNTIME(SELECTNBRECV, "runtime.selectnbrecv", P2(POINTER, CHAN), R1(BOOL))
-
-// Non-blocking tuple receive from a channel, used for two-case select
-// statement with a default case.
-DEF_GO_RUNTIME(SELECTNBRECV2, "runtime.selectnbrecv2", P3(POINTER, POINTER, CHAN),
-               R1(BOOL))
+DEF_GO_RUNTIME(SELECTNBRECV, "runtime.selectnbrecv", P2(POINTER, CHAN),
+	       R2(BOOL, BOOL))
 
 // Block execution.  Used for zero-case select.
 DEF_GO_RUNTIME(BLOCK, "runtime.block", P0(), R0())
diff --git a/gcc/go/gofrontend/statements.cc b/gcc/go/gofrontend/statements.cc
index 9643d1b..95fa3c4 100644
--- a/gcc/go/gofrontend/statements.cc
+++ b/gcc/go/gofrontend/statements.cc
@@ -6051,7 +6051,7 @@ Select_statement::lower_two_case(Block* b)
   Expression* chanref = Expression::make_temporary_reference(chantmp, loc);
 
   Block* bchan;
-  Expression* call;
+  Expression* cond;
   if (chancase.is_send())
     {
       // if selectnbsend(chan, &val) { body } else { default body }
@@ -6065,7 +6065,7 @@ Select_statement::lower_two_case(Block* b)
 
       Expression* ref = Expression::make_temporary_reference(ts, loc);
       Expression* addr = Expression::make_unary(OPERATOR_AND, ref, loc);
-      call = Runtime::make_call(Runtime::SELECTNBSEND, loc, 2, chanref, addr);
+      cond = Runtime::make_call(Runtime::SELECTNBSEND, loc, 2, chanref, addr);
       bchan = chancase.statements();
     }
   else
@@ -6075,34 +6075,31 @@ Select_statement::lower_two_case(Block* b)
 
       Expression* ref = Expression::make_temporary_reference(ts, loc);
       Expression* addr = Expression::make_unary(OPERATOR_AND, ref, loc);
-      Expression* okref = NULL;
-      if (chancase.closed() == NULL && chancase.closedvar() == NULL)
-        {
-          // Simple receive.
-          // if selectnbrecv(&lhs, chan) { body } else { default body }
-          call = Runtime::make_call(Runtime::SELECTNBRECV, loc, 2, addr, chanref);
-        }
-      else
-        {
-          // Tuple receive.
-          // if selectnbrecv2(&lhs, &ok, chan) { body } else { default body }
-
-          Type* booltype = Type::make_boolean_type();
-          Temporary_statement* okts = Statement::make_temporary(booltype, NULL,
-                                                                loc);
-          b->add_statement(okts);
-
-          okref = Expression::make_temporary_reference(okts, loc);
-          Expression* okaddr = Expression::make_unary(OPERATOR_AND, okref, loc);
-          call = Runtime::make_call(Runtime::SELECTNBRECV2, loc, 3, addr, okaddr,
-                                    chanref);
-        }
+
+      // selected, ok = selectnbrecv(&lhs, chan)
+      Call_expression* call = Runtime::make_call(Runtime::SELECTNBRECV, loc, 2,
+						 addr, chanref);
+
+      Temporary_statement* selected_temp =
+	Statement::make_temporary(Type::make_boolean_type(),
+				  Expression::make_call_result(call, 0),
+				  loc);
+      b->add_statement(selected_temp);
+
+      Temporary_statement* ok_temp =
+	Statement::make_temporary(Type::make_boolean_type(),
+				  Expression::make_call_result(call, 1),
+				  loc);
+      b->add_statement(ok_temp);
+
+      cond = Expression::make_temporary_reference(selected_temp, loc);
 
       Location cloc = chancase.location();
       bchan = new Block(b, loc);
       if (chancase.val() != NULL && !chancase.val()->is_sink_expression())
         {
-          Statement* as = Statement::make_assignment(chancase.val(), ref->copy(),
+          Statement* as = Statement::make_assignment(chancase.val(),
+						     ref->copy(),
                                                      cloc);
           bchan->add_statement(as);
         }
@@ -6114,12 +6111,18 @@ Select_statement::lower_two_case(Block* b)
 
       if (chancase.closed() != NULL && !chancase.closed()->is_sink_expression())
         {
+	  Expression* okref = Expression::make_temporary_reference(ok_temp,
+								   cloc);
           Statement* as = Statement::make_assignment(chancase.closed(),
-                                                     okref->copy(), cloc);
+                                                     okref, cloc);
           bchan->add_statement(as);
         }
       else if (chancase.closedvar() != NULL)
-        chancase.closedvar()->var_value()->set_init(okref->copy());
+	{
+	  Expression* okref = Expression::make_temporary_reference(ok_temp,
+								   cloc);
+	  chancase.closedvar()->var_value()->set_init(okref);
+	}
 
       Statement* bs = Statement::make_block_statement(chancase.statements(),
                                                       cloc);
@@ -6127,7 +6130,7 @@ Select_statement::lower_two_case(Block* b)
     }
 
   Statement* ifs =
-    Statement::make_if_statement(call, bchan, defcase.statements(), loc);
+    Statement::make_if_statement(cond, bchan, defcase.statements(), loc);
   b->add_statement(ifs);
 
   Statement* label =
diff --git a/libgo/go/runtime/chan.go b/libgo/go/runtime/chan.go
index 7878a8f..e3d0ad5 100644
--- a/libgo/go/runtime/chan.go
+++ b/libgo/go/runtime/chan.go
@@ -33,7 +33,6 @@ import (
 //go:linkname closechan
 //go:linkname selectnbsend
 //go:linkname selectnbrecv
-//go:linkname selectnbrecv2
 
 const (
 	maxAlign  = 8
@@ -712,28 +711,6 @@ func selectnbsend(c *hchan, elem unsafe.Pointer) (selected bool) {
 // compiler implements
 //
 //	select {
-//	case v = <-c:
-//		... foo
-//	default:
-//		... bar
-//	}
-//
-// as
-//
-//	if selectnbrecv(&v, c) {
-//		... foo
-//	} else {
-//		... bar
-//	}
-//
-func selectnbrecv(elem unsafe.Pointer, c *hchan) (selected bool) {
-	selected, _ = chanrecv(c, elem, false)
-	return
-}
-
-// compiler implements
-//
-//	select {
 //	case v, ok = <-c:
 //		... foo
 //	default:
@@ -742,16 +719,14 @@ func selectnbrecv(elem unsafe.Pointer, c *hchan) (selected bool) {
 //
 // as
 //
-//	if c != nil && selectnbrecv2(&v, &ok, c) {
+//	if selected, ok = selectnbrecv(&v, c); selected {
 //		... foo
 //	} else {
 //		... bar
 //	}
 //
-func selectnbrecv2(elem unsafe.Pointer, received *bool, c *hchan) (selected bool) {
-	// TODO(khr): just return 2 values from this function, now that it is in Go.
-	selected, *received = chanrecv(c, elem, false)
-	return
+func selectnbrecv(elem unsafe.Pointer, c *hchan) (selected, received bool) {
+	return chanrecv(c, elem, false)
 }
 
 //go:linkname reflect_chansend reflect.chansend