shithub: riscv

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ref: d6a91e0ae47b4e1df9a9783c49666e2a7357e277
parent: cfafa676408057a7434ec81e5dc15ae0ffba91f2
author: cinap_lenrek <cinap_lenrek@felloff.net>
date: Tue May 26 15:25:06 EDT 2015 

cc: set unspecified elements to zero in local variable initializers

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 */
}


--- a/sys/src/cmd/cc/dcl.c
+++ b/sys/src/cmd/cc/dcl.c
@@ -1542,6 +1542,48 @@
 	}
 }
 
+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 @@
 	}
 	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)
@@ -1589,47 +1625,29 @@
 
 	v = s->offset;
 
-	/* unaligned front */ 
-	while(w > 0 && (v % ewidth[TIND]) != 0){
-		p = new(ONAME, Z, Z);
-		*p = *q;
-
+	/* unaligned front */
+	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)