gc: allow taking address of out parameters

Fixes issue 186.

R=ken2
CC=golang-dev
http://codereview.appspot.com/793041

5 files changed, 95 insertions, 11 deletions

diff --git a/src/cmd/5g/ggen.c b/src/cmd/5g/ggen.c
index e2313d85b..c60c05863 100644
--- a/src/cmd/5g/ggen.c
+++ b/src/cmd/5g/ggen.c
@@ -7,6 +7,8 @@
 #include "gg.h"
 #include "opt.h"
 
+static Prog *pret;
+
 void
 compile(Node *fn)
 {
@@ -65,6 +67,16 @@ compile(Node *fn)
 	afunclit(&ptxt->from);
 
 	genlist(curfn->enter);
+	
+	pret = nil;
+	if(hasdefer || curfn->exit) {
+		Prog *p1;
+
+		p1 = gjmp(nil);
+		pret = gjmp(nil);
+		patch(p1, pc);
+	}
+
 	genlist(curfn->nbody);
 	checklabels();
 	if(nerrors != 0)
@@ -73,6 +85,14 @@ compile(Node *fn)
 	if(curfn->type->outtuple != 0)
 		ginscall(throwreturn, 0);
 
+	if(pret)
+		patch(pret, pc);
+	ginit();
+	if(curfn->exit)
+		genlist(curfn->exit);
+	gclean();
+	if(nerrors != 0)
+		goto ret;
 	if(hasdefer)
 		ginscall(deferreturn, 0);
 	pc->as = ARET;	// overwrite AEND
diff --git a/src/cmd/6g/ggen.c b/src/cmd/6g/ggen.c
index 99a4aea04..140020fda 100644
--- a/src/cmd/6g/ggen.c
+++ b/src/cmd/6g/ggen.c
@@ -7,6 +7,8 @@
 #include "gg.h"
 #include "opt.h"
 
+static Prog *pret;
+
 void
 compile(Node *fn)
 {
@@ -66,6 +68,16 @@ compile(Node *fn)
 
 	ginit();
 	genlist(curfn->enter);
+
+	pret = nil;
+	if(hasdefer || curfn->exit) {
+		Prog *p1;
+
+		p1 = gjmp(nil);
+		pret = gjmp(nil);
+		patch(p1, pc);
+	}
+
 	genlist(curfn->nbody);
 	gclean();
 	checklabels();
@@ -75,6 +87,14 @@ compile(Node *fn)
 	if(curfn->type->outtuple != 0)
 		ginscall(throwreturn, 0);
 
+	if(pret)
+		patch(pret, pc);
+	ginit();
+	if(curfn->exit)
+		genlist(curfn->exit);
+	gclean();
+	if(nerrors != 0)
+		goto ret;
 	if(hasdefer)
 		ginscall(deferreturn, 0);
 	pc->as = ARET;	// overwrite AEND
@@ -325,9 +345,10 @@ void
 cgen_ret(Node *n)
 {
 	genlist(n->list);		// copy out args
-	if(hasdefer)
-		ginscall(deferreturn, 0);
-	gins(ARET, N, N);
+	if(hasdefer || curfn->exit)
+		gjmp(pret);
+	else
+		gins(ARET, N, N);
 }
 
 /*
diff --git a/src/cmd/8g/ggen.c b/src/cmd/8g/ggen.c
index 23177c240..468f67ae9 100644
--- a/src/cmd/8g/ggen.c
+++ b/src/cmd/8g/ggen.c
@@ -7,6 +7,8 @@
 #include "gg.h"
 #include "opt.h"
 
+static Prog *pret;
+
 void
 compile(Node *fn)
 {
@@ -66,6 +68,16 @@ compile(Node *fn)
 
 	ginit();
 	genlist(curfn->enter);
+
+	pret = nil;
+	if(hasdefer || curfn->exit) {
+		Prog *p1;
+
+		p1 = gjmp(nil);
+		pret = gjmp(nil);
+		patch(p1, pc);
+	}
+
 	genlist(curfn->nbody);
 	gclean();
 	checklabels();
@@ -75,6 +87,14 @@ compile(Node *fn)
 	if(curfn->type->outtuple != 0)
 		ginscall(throwreturn, 0);
 
+	if(pret)
+		patch(pret, pc);
+	ginit();
+	if(curfn->exit)
+		genlist(curfn->exit);
+	gclean();
+	if(nerrors != 0)
+		goto ret;
 	if(hasdefer)
 		ginscall(deferreturn, 0);
 	pc->as = ARET;	// overwrite AEND
@@ -362,9 +382,10 @@ void
 cgen_ret(Node *n)
 {
 	genlist(n->list);		// copy out args
-	if(hasdefer)
-		ginscall(deferreturn, 0);
-	gins(ARET, N, N);
+	if(pret)
+		gjmp(pret);
+	else
+		gins(ARET, N, N);
 }
 
 /*
diff --git a/src/cmd/gc/typecheck.c b/src/cmd/gc/typecheck.c
index d10bf8f74..c219ad8c5 100644
--- a/src/cmd/gc/typecheck.c
+++ b/src/cmd/gc/typecheck.c
@@ -1988,17 +1988,15 @@ addrescapes(Node *n)
 		if(n->noescape)
 			break;
 		switch(n->class) {
-		case PPARAMOUT:
-			yyerror("cannot take address of out parameter %s", n->sym->name);
-			break;
 		case PAUTO:
 		case PPARAM:
+		case PPARAMOUT:
 			// if func param, need separate temporary
 			// to hold heap pointer.
 			// the function type has already been checked
 			// (we're in the function body)
 			// so the param already has a valid xoffset.
-			if(n->class == PPARAM) {
+			if(n->class == PPARAM || n->class == PPARAMOUT) {
 				// expression to refer to stack copy
 				n->stackparam = nod(OPARAM, n, N);
 				n->stackparam->type = n->type;
diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 9c904f14c..fa6157bb0 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -2288,7 +2288,29 @@ paramstoheap(Type **argin)
 		if(v->alloc == nil)
 			v->alloc = callnew(v->type);
 		nn = list(nn, nod(OAS, v->heapaddr, v->alloc));
-		nn = list(nn, nod(OAS, v, v->stackparam));
+		if((v->class & ~PHEAP) != PPARAMOUT)
+			nn = list(nn, nod(OAS, v, v->stackparam));
+	}
+	return nn;
+}
+
+/*
+ * walk through argout parameters copying back to stack
+ */
+NodeList*
+returnsfromheap(Type **argin)
+{
+	Type *t;
+	Iter savet;
+	Node *v;
+	NodeList *nn;
+
+	nn = nil;
+	for(t = structfirst(&savet, argin); t != T; t = structnext(&savet)) {
+		v = t->nname;
+		if(v == N || v->class != (PHEAP|PPARAMOUT))
+			continue;
+		nn = list(nn, nod(OAS, v->stackparam, v));
 	}
 	return nn;
 }
@@ -2305,7 +2327,9 @@ heapmoves(void)
 
 	nn = paramstoheap(getthis(curfn->type));
 	nn = concat(nn, paramstoheap(getinarg(curfn->type)));
+	nn = concat(nn, paramstoheap(getoutarg(curfn->type)));
 	curfn->enter = concat(curfn->enter, nn);
+	curfn->exit = returnsfromheap(getoutarg(curfn->type));
 }
 
 static Node*