fix edge deletion bug in sccp

When an edge is deleted, the phis and predecessors of the
destination block have to be updated.  This is what blkdel()
was doing, but at a level too coarse.  The new function
edgedel() allows to remove a single edge (and takes care of
multiple edges).

all.h

@@ -547,7 +547,7 @@ void err(char *, ...) __attribute__((noreturn));
 
 /* cfg.c */
 Blk *blknew(void);
-void blkdel(Blk *);
+void edgedel(Blk *, Blk **);
 void fillpreds(Fn *);
 void fillrpo(Fn *);
 void filldom(Fn *);

cfg.c

@@ -12,32 +12,33 @@ blknew()
 }
 
 void
-blkdel(Blk *b)
+edgedel(Blk *bs, Blk **pbd)
 {
-	Blk *s, **ps, *succ[3];
+	Blk *bd;
 	Phi *p;
 	uint a;
+	int mult;
 
-	succ[0] = b->s1;
-	succ[1] = b->s2 == b->s1 ? 0 : b->s2;
-	succ[2] = 0;
-	for (ps=succ; (s=*ps); ps++) {
-		for (p=s->phi; p; p=p->link) {
-			for (a=0; p->blk[a]!=b; a++)
-				assert(a+1<p->narg);
-			p->narg--;
-			memmove(&p->blk[a], &p->blk[a+1],
-				sizeof p->blk[0] * (p->narg-a));
-			memmove(&p->arg[a], &p->arg[a+1],
-				sizeof p->arg[0] * (p->narg-a));
-		}
-		if (s->npred != 0) {
-			for (a=0; s->pred[a]!=b; a++)
-				assert(a+1<s->npred);
-			s->npred--;
-			memmove(&s->pred[a], &s->pred[a+1],
-				sizeof s->pred[0] * (s->npred-a));
-		}
+	bd = *pbd;
+	mult = 1 + (bs->s1 == bs->s2);
+	*pbd = 0;
+	if (!bd || mult > 1)
+		return;
+	for (p=bd->phi; p; p=p->link) {
+		for (a=0; p->blk[a]!=bs; a++)
+			assert(a+1<p->narg);
+		p->narg--;
+		memmove(&p->blk[a], &p->blk[a+1],
+			sizeof p->blk[0] * (p->narg-a));
+		memmove(&p->arg[a], &p->arg[a+1],
+			sizeof p->arg[0] * (p->narg-a));
+	}
+	if (bd->npred != 0) {
+		for (a=0; bd->pred[a]!=bs; a++)
+			assert(a+1<bd->npred);
+		bd->npred--;
+		memmove(&bd->pred[a], &bd->pred[a+1],
+			sizeof bd->pred[0] * (bd->npred-a));
 	}
 }
 
@@ -110,7 +111,8 @@ fillrpo(Fn *f)
 	f->rpo = alloc(f->nblk * sizeof f->rpo[0]);
 	for (p=&f->start; (b=*p);) {
 		if (b->id == -1u) {
-			blkdel(b);
+			edgedel(b, &b->s1);
+			edgedel(b, &b->s2);
 			*p = b->link;
 		} else {
 			b->id -= n;

fold.c

@@ -275,7 +275,8 @@ fold(Fn *fn)
 			d = 1;
 			if (debug['F'])
 				fprintf(stderr, "%s ", b->name);
-			blkdel(b);
+			edgedel(b, &b->s1);
+			edgedel(b, &b->s2);
 			*pb = b->link;
 			continue;
 		}
@@ -296,11 +297,14 @@ fold(Fn *fn)
 					renref(&i->arg[n]);
 		renref(&b->jmp.arg);
 		if (b->jmp.type == Jjnz && rtype(b->jmp.arg) == RCon) {
-				b->jmp.type = Jjmp;
-				if (czero(&fn->con[b->jmp.arg.val], 0))
+				if (czero(&fn->con[b->jmp.arg.val], 0)) {
+					edgedel(b, &b->s1);
 					b->s1 = b->s2;
+					b->s2 = 0;
+				} else
+					edgedel(b, &b->s2);
+				b->jmp.type = Jjmp;
 				b->jmp.arg = R;
-				b->s2 = 0;
 		}
 		pb = &b->link;
 	}