From e73674b291a2029297d2188293de796885f083fa Mon Sep 17 00:00:00 2001
From: Ken Thompson <ken@golang.org>
Date: Mon, 31 Mar 2008 19:19:37 -0700
Subject: [PATCH] code to assign nil to an interface without conversions

SVN=114453
---
 src/c/gen.c   | 28 ++++++++++++++++++----------
 src/c/gen.h   |  2 +-
 src/c/go.h    |  1 +
 src/c/gsubr.c |  1 +
 src/c/obj.c   | 21 +++++++++++++++++++++
 src/c/subr.c  | 12 ++++++++++++
 6 files changed, 54 insertions(+), 11 deletions(-)

diff --git a/src/c/gen.c b/src/c/gen.c
index 0644d17651..99993145b7 100644
--- a/src/c/gen.c
+++ b/src/c/gen.c
@@ -827,19 +827,19 @@ loop:
 			break;
 
 		case PAS_SINGLE: // single return val used in expr
-			if(nr == N) {
+			if(nr == N || isnil(nr)) {
 				if(nl->addable) {
 					gopcodet(PSTOREZ, nl->type, nl);
 					break;
 				}
 				agen(nl);
-				gopcodet(PSTOREZIP, nl->type, N);
+				gopcodet(PSTOREZI, nl->type, N);
 				break;
 			}
 
 			if(nl->addable) {
 				cgen(nr);
-				genconv(nl->type, nr->type);
+				genconv(nl, nr);
 				gopcodet(PSTORE, nl->type, nl);
 				break;
 			}
@@ -851,7 +851,7 @@ loop:
 			}
 			if(!usesptr(nr)) {
 				cgen(nr);
-				genconv(nl->type, nr->type);
+				genconv(nl, nr);
 				agen(nl);
 				gopcodet(PSTOREI, nr->type, N);
 				break;
@@ -860,7 +860,7 @@ loop:
 			r = tempname(ptrto(nl->type));
 			gopcode(PSTORE, PTADDR, r);
 			cgen(nr);
-			genconv(nl->type, nr->type);
+			genconv(nl, nr);
 			gopcode(PLOAD, PTADDR, r);
 			gopcodet(PSTOREI, nl->type, N);
 			break;
@@ -964,7 +964,7 @@ cgen_ret(Node *n)
 			gopcodet(PSTOREI, arg->type, arg);
 		} else {
 			cgen(arg);
-			genconv(f->type, arg->type);
+			genconv(f, arg);
 			gopcode(PLOAD, PTADDR, a->nname);
 			gopcode(PADDO, PTADDR, f->nname);
 			gopcodet(PSTOREI, f->type, N);
@@ -1010,7 +1010,7 @@ cgen_call(Node *n, int toss)
 			gopcodet(PSTOREI, at->type, ae);
 		} else {
 			cgen(ae);
-			genconv(at->type, ae->type);
+			genconv(at, ae);
 			gopcode(PADDR, PTADDR, sn);
 			gopcode(PADDO, PTADDR, at->nname);
 			gopcodet(PSTOREI, at->type, N);
@@ -1120,9 +1120,13 @@ genprint(Node *n)
 int
 needconvert(Node *tl, Node *tr)
 {
-	if(isinter(tl))
-		if(isptrto(tr, TSTRUCT) || isinter(tr))
+	if(isinter(tl)) {
+		if(isptrto(tr, TSTRUCT))
 			return 1;
+		if(isinter(tr))
+			return 1;
+		return 0;
+	}
 	if(isptrto(tl, TSTRUCT))
 		if(isinter(tr))
 			return 1;
@@ -1130,8 +1134,12 @@ needconvert(Node *tl, Node *tr)
 }
 
 void
-genconv(Node *tl, Node *tr)
+genconv(Node *l, Node *r)
 {
+	Node *tl, *tr;
+
+	tl = l->type;
+	tr = r->type;
 	if(needconvert(tl, tr))
 		gopcode(PCONV, PTNIL, nod(OCONV, tl, tr));
 }
diff --git a/src/c/gen.h b/src/c/gen.h
index 13383141ad..9ccef59265 100644
--- a/src/c/gen.h
+++ b/src/c/gen.h
@@ -103,7 +103,7 @@ enum
 
 	PLOAD, PLOADI,
 	PSTORE, PSTOREI,
-	PSTOREZ, PSTOREZIP,
+	PSTOREZ, PSTOREZI,
 	PCONV, PADDR, PADDO, PINDEX, PINDEXZ,
 	PSLICE,
 
diff --git a/src/c/go.h b/src/c/go.h
index 73cc8da1c9..003bb0d2e4 100644
--- a/src/c/go.h
+++ b/src/c/go.h
@@ -395,6 +395,7 @@ Node*	unrev(Node*);
 void	dodump(Node*, int);
 void	dump(char*, Node*);
 Node*	aindex(Node*, Node*);
+int	isnil(Node*);
 int	isptrto(Node*, int);
 int	isinter(Node*);
 int	isbytearray(Node*);
diff --git a/src/c/gsubr.c b/src/c/gsubr.c
index bf6c31b578..2ac8ea8cf0 100644
--- a/src/c/gsubr.c
+++ b/src/c/gsubr.c
@@ -236,6 +236,7 @@ pnames[] =
 	[PSTORE]	= "STORE",
 	[PSTOREI]	= "STOREI",
 	[PSTOREZ]	= "STOREZ",
+	[PSTOREZI]	= "STOREZI",
 	[PCONV]		= "CONV",
 	[PADDR]		= "ADDR",
 	[PADDO]		= "ADDO",
diff --git a/src/c/obj.c b/src/c/obj.c
index 2c220226cd..f44a0f0832 100644
--- a/src/c/obj.c
+++ b/src/c/obj.c
@@ -243,6 +243,27 @@ obj1(Prog *p)
 		}
 		break;
 
+	case PSTOREZI:
+		switch(p->pt) {
+		default:
+			Bprint(bout, "\t*(%Q*)%R = 0;\n", p->pt, PTADDR);
+			break;
+
+		case PTARRAY:
+		case PTSTRUCT:
+			Bprint(bout, "\tmemset((%Q*)%R, 0, sizeof((%Q*)%R));\n", p->pt, PTADDR, p->pt, PTADDR);
+			break;
+
+		case PTINTER:
+			Bprint(bout, "\t((%Q*)%R)->s = 0; ((%Q*)%R)->m = 0;\n", p->pt, PTADDR, p->pt, PTADDR);
+			break;
+
+		case PTSTRING:
+			Bprint(bout, "\t(%Q*)%R = &nilstring;\n", p->pt, PTADDR);
+			break;
+		}
+		break;
+
 	case PCONV:
 		doconv(p);
 		break;
diff --git a/src/c/subr.c b/src/c/subr.c
index 052179c9ed..e03cf85850 100644
--- a/src/c/subr.c
+++ b/src/c/subr.c
@@ -997,6 +997,18 @@ out:
 	return fmtstrcpy(fp, buf);
 }
 
+int
+isnil(Node *n)
+{
+	if(n == N)
+		return 0;
+	if(n->op != OLITERAL)
+		return 0;
+	if(n->val.ctype != CTNIL)
+		return 0;
+	return 1;
+}
+
 int
 isptrto(Node *t, int et)
 {
-- 
2.48.1