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// 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(safemode || fn == N || fn->op != ONAME || (s = fn->sym) == S)
goto no;
if(s->pkg != unsafepkg)
goto no;
if(args == nil) {
yyerror("missing argument for %S", s);
goto no;
}
r = args->n;
if(strcmp(s->name, "Sizeof") == 0) {
typecheck(&r, Erv);
defaultlit(&r, T);
tr = r->type;
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);
defaultlit(&r, T);
tr = r->type;
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;
}
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