From 1246ad8390c72211e98602895791a204440227fb Mon Sep 17 00:00:00 2001
From: Ken Thompson <ken@golang.org>
Date: Tue, 29 Jun 2010 12:48:24 -0700
Subject: [PATCH] code gen bug in len(nil) and cap(nil) fixes #892

R=rsc
CC=golang-dev
https://golang.org/cl/1745042
---
 src/cmd/5g/gsubr.c | 4 ++++
 src/cmd/6g/gsubr.c | 4 ++++
 src/cmd/8g/gsubr.c | 4 ++++
 3 files changed, 12 insertions(+)

diff --git a/src/cmd/5g/gsubr.c b/src/cmd/5g/gsubr.c
index ea6ab1d70bc..700602c3501 100644
--- a/src/cmd/5g/gsubr.c
+++ b/src/cmd/5g/gsubr.c
@@ -1137,6 +1137,8 @@ naddr(Node *n, Addr *a, int canemitcode)
 	case OLEN:
 		// len of string or slice
 		naddr(n->left, a, canemitcode);
+		if(a->type == D_CONST && a->offset == 0)
+			break;	// len(nil)
 		a->offset += Array_nel;
 		if(a->offset >= unmappedzero && a->offset-Array_nel < unmappedzero)
 			checkoffset(a, canemitcode);
@@ -1145,6 +1147,8 @@ naddr(Node *n, Addr *a, int canemitcode)
 	case OCAP:
 		// cap of string or slice
 		naddr(n->left, a, canemitcode);
+		if(a->type == D_CONST && a->offset == 0)
+			break;	// cap(nil)
 		a->offset += Array_cap;
 		if(a->offset >= unmappedzero && a->offset-Array_cap < unmappedzero)
 			checkoffset(a, canemitcode);
diff --git a/src/cmd/6g/gsubr.c b/src/cmd/6g/gsubr.c
index 1c11b14aebb..52ff6fdea2d 100644
--- a/src/cmd/6g/gsubr.c
+++ b/src/cmd/6g/gsubr.c
@@ -1079,6 +1079,8 @@ naddr(Node *n, Addr *a, int canemitcode)
 	case OLEN:
 		// len of string or slice
 		naddr(n->left, a, canemitcode);
+		if(a->type == D_CONST && a->offset == 0)
+			break;	// len(nil)
 		a->etype = TUINT;
 		a->offset += Array_nel;
 		if(a->offset >= unmappedzero && a->offset-Array_nel < unmappedzero)
@@ -1088,6 +1090,8 @@ naddr(Node *n, Addr *a, int canemitcode)
 	case OCAP:
 		// cap of string or slice
 		naddr(n->left, a, canemitcode);
+		if(a->type == D_CONST && a->offset == 0)
+			break;	// cap(nil)
 		a->etype = TUINT;
 		a->offset += Array_cap;
 		if(a->offset >= unmappedzero && a->offset-Array_cap < unmappedzero)
diff --git a/src/cmd/8g/gsubr.c b/src/cmd/8g/gsubr.c
index 3e85b7e30e8..6890c683e6f 100644
--- a/src/cmd/8g/gsubr.c
+++ b/src/cmd/8g/gsubr.c
@@ -1789,6 +1789,8 @@ naddr(Node *n, Addr *a, int canemitcode)
 	case OLEN:
 		// len of string or slice
 		naddr(n->left, a, canemitcode);
+		if(a->type == D_CONST && a->offset == 0)
+			break;	// len(nil)
 		a->etype = TUINT;
 		a->offset += Array_nel;
 		if(a->offset >= unmappedzero && a->offset-Array_nel < unmappedzero)
@@ -1798,6 +1800,8 @@ naddr(Node *n, Addr *a, int canemitcode)
 	case OCAP:
 		// cap of string or slice
 		naddr(n->left, a, canemitcode);
+		if(a->type == D_CONST && a->offset == 0)
+			break;	// cap(nil)
 		a->etype = TUINT;
 		a->offset += Array_cap;
 		if(a->offset >= unmappedzero && a->offset-Array_nel < unmappedzero)