From 651972b31f7da9a1d522fc427a6d6693070f1cb5 Mon Sep 17 00:00:00 2001
From: Ian Lance Taylor <iant@golang.org>
Date: Tue, 10 Feb 2009 11:46:26 -0800
Subject: [PATCH] Implement unsafe.Alignof.

R=ken
DELTA=20  (19 added, 0 deleted, 1 changed)
OCL=24719
CL=24771
---
 src/cmd/gc/dcl.c       | 19 ++++++++++++++++++-
 src/cmd/gc/sysimport.c |  1 +
 src/cmd/gc/unsafe.go   |  1 +
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/cmd/gc/dcl.c b/src/cmd/gc/dcl.c
index d5d3a9bf4df..35d1a8e62b6 100644
--- a/src/cmd/gc/dcl.c
+++ b/src/cmd/gc/dcl.c
@@ -1495,6 +1495,7 @@ unsafenmagic(Node *l, Node *r)
 {
 	Node *n;
 	Sym *s;
+	Type *t;
 	long v;
 	Val val;
 
@@ -1519,7 +1520,23 @@ unsafenmagic(Node *l, Node *r)
 		if(r->op != ODOT && r->op != ODOTPTR)
 			goto no;
 		walktype(r, Erv);
-		v = n->xoffset;
+		v = r->xoffset;
+		goto yes;
+	}
+	if(strcmp(s->name, "Alignof") == 0) {
+		walktype(r, Erv);
+		if (r->type == T)
+			goto no;
+		// make struct { byte; T; }
+		t = typ(TSTRUCT);
+		t->type = typ(TFIELD);
+		t->type->type = types[TUINT8];
+		t->type->down = typ(TFIELD);
+		t->type->down->type = r->type;
+		// compute struct widths
+		dowidth(t);
+		// the offset of T is its required alignment
+		v = t->type->down->width;
 		goto yes;
 	}
 
diff --git a/src/cmd/gc/sysimport.c b/src/cmd/gc/sysimport.c
index 4d682d675d0..ccc38343d7e 100644
--- a/src/cmd/gc/sysimport.c
+++ b/src/cmd/gc/sysimport.c
@@ -67,5 +67,6 @@ char *unsafeimport =
 	"type unsafe.Pointer *any\n"
 	"func unsafe.Offsetof (? any) (? int)\n"
 	"func unsafe.Sizeof (? any) (? int)\n"
+	"func unsafe.Alignof (? any) (? int)\n"
 	"\n"
 	"$$\n";
diff --git a/src/cmd/gc/unsafe.go b/src/cmd/gc/unsafe.go
index 47703f6e0ff..d1dcee02a83 100644
--- a/src/cmd/gc/unsafe.go
+++ b/src/cmd/gc/unsafe.go
@@ -8,3 +8,4 @@ package PACKAGE
 type	Pointer	*any;
 func	Offsetof(any) int;
 func	Sizeof(any) int;
+func	Alignof(any) int;