1 files changed, 87 insertions, 0 deletions
diff --git a/src/cmd/gc/unsafe.c b/src/cmd/gc/unsafe.c
new file mode 100644
index 000000000..9c1f9519a
--- /dev/null
+++ b/src/cmd/gc/unsafe.c
@@ -0,0 +1,87 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "go.h"
+
+/*
+ * look for
+ *	unsafe.Sizeof
+ *	unsafe.Offsetof
+ * rewrite with a constant
+ */
+Node*
+unsafenmagic(Node *fn, NodeList *args)
+{
+	Node *r, *n;
+	Sym *s;
+	Type *t, *tr;
+	long v;
+	Val val;
+
+	if(fn == N || fn->op != ONAME || (s = fn->sym) == S)
+		goto no;
+	if(strcmp(s->package, "unsafe") != 0)
+		goto no;
+
+	if(args == nil) {
+		yyerror("missing argument for %S", s);
+		goto no;
+	}
+	r = args->n;
+
+	n = nod(OLITERAL, N, N);
+	if(strcmp(s->name, "Sizeof") == 0) {
+		typecheck(&r, Erv);
+		tr = r->type;
+		if(r->op == OLITERAL && r->val.ctype == CTSTR)
+			tr = types[TSTRING];
+		if(tr == T)
+			goto no;
+		v = tr->width;
+		goto yes;
+	}
+	if(strcmp(s->name, "Offsetof") == 0) {
+		if(r->op != ODOT && r->op != ODOTPTR)
+			goto no;
+		typecheck(&r, Erv);
+		v = r->xoffset;
+		goto yes;
+	}
+	if(strcmp(s->name, "Alignof") == 0) {
+		typecheck(&r, Erv);
+		tr = r->type;
+		if(r->op == OLITERAL && r->val.ctype == CTSTR)
+			tr = types[TSTRING];
+		if(tr == 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 = tr;
+		// compute struct widths
+		dowidth(t);
+
+		// the offset of T is its required alignment
+		v = t->type->down->width;
+		goto yes;
+	}
+
+no:
+	return N;
+
+yes:
+	if(args->next != nil)
+		yyerror("extra arguments for %S", s);
+	// any side effects disappear; ignore init
+	val.ctype = CTINT;
+	val.u.xval = mal(sizeof(*n->val.u.xval));
+	mpmovecfix(val.u.xval, v);
+	n = nod(OLITERAL, N, N);
+	n->val = val;
+	n->type = types[TINT];
+	return n;
+}