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cc: set unspecified elements to zero in local variable initializers

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the compiler used to skip zero initialization when initializer
list was given not covering unspecified elements. now we zero
all non explicitely initialized elements. for example:

typedef struct F F;
struct F
{
	int a;
	int b;
	int c;
};

void
main(void)
{
	char a[16] = { 1, 2, 3 };	/* a[3..15] initialized to zero */
	F f = { .b = 1 };			/* f.a, f.c initialized to zero */
}
This commit is contained in:
cinap_lenrek 2015-05-26 19:25:06 +02:00
parent cfafa67640
commit d6a91e0ae4
1 changed files with 59 additions and 41 deletions
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98
sys/src/cmd/cc/dcl.c
View file

@ -1542,6 +1542,48 @@ symadjust(Sym *s, Node *n, long del)
}
}
static int
covered1(long o, Node *n)
{
if(n->op == OLIST)
return covered1(o, n->left) || covered1(o, n->right);
if(n->op == OASI)
return covered1(o, n->left);
if(n->op != ONAME)
return 0;
return o >= n->xoffset && o < n->xoffset+n->type->width;
}
static int
covered(long o, long w, Node *n)
{
while(w > 0 && covered1(o, n)) {
o++;
w--;
}
return w == 0;
}
static Node*
initz(Node *q, Type *t, long o, Node *n)
{
Node *p;
if(covered(o, t->width, n))
return n;
p = new(ONAME, Z, Z);
*p = *q;
p->type = t;
p->xoffset = o;
q = new(OCONST, Z, Z);
q->vconst = 0;
q->type = t;
return new(OLIST, new(OASI, p, q), n);
}
Node*
contig(Sym *s, Node *n, long v)
{
@ -1573,12 +1615,6 @@ contig(Sym *s, Node *n, long v)
}
if(n->op == OAS)
diag(Z, "oops in contig");
/*ZZZ this appears incorrect
need to check if the list completely covers the data.
if not, bail
*/
if(n->op == OLIST)
goto no;
if(n->op == OASI)
if(n->left->type)
if(n->left->type->width == w)
@ -1590,46 +1626,28 @@ if not, bail
v = s->offset;
/* unaligned front */
while(w > 0 && (v % ewidth[TIND]) != 0){
p = new(ONAME, Z, Z);
*p = *q;
while(w > 0 && (v % ewidth[TIND]) != 0) {
zt = types[TCHAR];
if(w >= ewidth[TLONG] && (v % ewidth[TLONG]) == 0)
p->type = types[TLONG];
else
p->type = types[TCHAR];
zt = types[TLONG];
n = initz(q, zt, v, n);
v += zt->width;
w -= zt->width;
}
p->xoffset = v;
v += p->type->width;
w -= p->type->width;
m = new(OCONST, Z, Z);
m->vconst = 0;
m->type = p->type;
r = new(OAS, p, m);
n = new(OLIST, r, n);
/* skip initialized words */
while(w >= ewidth[TIND] && covered(v, ewidth[TIND], n)) {
v += ewidth[TIND];
w -= ewidth[TIND];
}
/* unaligned (or small) back */
while(w > 0 && ((w % ewidth[TIND]) != 0 || w <= 16)){
p = new(ONAME, Z, Z);
*p = *q;
while(w > 0 && ((w % ewidth[TIND]) != 0 || w <= 16)) {
zt = types[TCHAR];
if(w >= ewidth[TLONG] && (w % ewidth[TLONG]) == 0)
p->type = types[TLONG];
else
p->type = types[TCHAR];
w -= p->type->width;
p->xoffset = v + w;
m = new(OCONST, Z, Z);
m->vconst = 0;
m->type = p->type;
r = new(OAS, p, m);
n = new(OLIST, r, n);
zt = types[TLONG];
w -= zt->width;
n = initz(q, zt, v + w, n);
}
if(w == 0)