commit 5e9726946dcb9248dbd34ded1bdd4f7af8dc2d31
parent c5cd65261e05029889450ca27050785504164853
Author: Quentin Carbonneaux <quentin@c9x.me>
Date: Sun, 18 Dec 2022 17:35:19 +0100
new UNDEF Ref
Crashing loads of uninitialized memory
proved to be a problem when implementing
unions using qbe. This patch introduces
a new UNDEF Ref to represent data that is
known to be uninitialized. Optimization
passes can make use of it to eliminate
some code. In the last compilation stages,
UNDEF is treated as the constant 0xdeaddead.
Diffstat:
8 files changed, 46 insertions(+), 28 deletions(-)
diff --git a/all.h b/all.h
@@ -90,10 +90,11 @@ enum {
RMem,
};
-#define R (Ref){0, 0}
+#define R (Ref){RTmp, 0}
+#define UNDEF (Ref){RCon, 0} /* represents uninitialized data */
+#define CON_Z (Ref){RCon, 1}
#define TMP(x) (Ref){RTmp, x}
#define CON(x) (Ref){RCon, x}
-#define CON_Z CON(0) /* reserved zero constant */
#define SLOT(x) (Ref){RSlot, (x)&0x1fffffff}
#define TYPE(x) (Ref){RType, x}
#define CALL(x) (Ref){RCall, x}
diff --git a/amd64/isel.c b/amd64/isel.c
@@ -482,7 +482,7 @@ seljmp(Blk *b, Fn *fn)
}
fi = flagi(b->ins, &b->ins[b->nins]);
if (!fi || !req(fi->to, r)) {
- selcmp((Ref[2]){r, CON_Z}, Kw, 0, fn); /* todo, long jnz */
+ selcmp((Ref[2]){r, CON_Z}, Kw, 0, fn);
b->jmp.type = Jjf + Cine;
}
else if (iscmp(fi->op, &k, &c)
diff --git a/copy.c b/copy.c
@@ -125,7 +125,7 @@ subst(Ref *pr, Ref *cpy)
*pr = copyof(*pr, cpy);
}
-/* requires use and rpo, breaks use */
+/* requires use and dom, breaks use */
void
copy(Fn *fn)
{
@@ -155,12 +155,16 @@ copy(Fn *fn)
for (a=0; a<p->narg; a++)
if (p->blk[a]->id < n) {
r1 = copyof(p->arg[a], cpy);
- if (req(r, R) || req(r1, r))
+ if (req(r, R) || req(r, UNDEF))
+ r = r1;
+ if (req(r1, r) || req(r1, UNDEF))
eq++;
- r = r1;
}
assert(!req(r, R));
- if (eq == p->narg)
+ if (rtype(r) == RTmp
+ && !dom(fn->rpo[fn->tmp[r.val].bid], b))
+ cpy[p->to.val] = p->to;
+ else if (eq == p->narg)
cpy[p->to.val] = r;
else {
cpy[p->to.val] = p->to;
diff --git a/fold.c b/fold.c
@@ -1,8 +1,8 @@
#include "all.h"
enum {
- Bot = -2, /* lattice bottom */
- Top = -1, /* lattice top */
+ Bot = -1, /* lattice bottom */
+ Top = 0, /* lattice top (matches UNDEF) */
};
typedef struct Edge Edge;
@@ -126,7 +126,6 @@ visitjmp(Blk *b, int n, Fn *fn)
switch (b->jmp.type) {
case Jjnz:
l = latval(b->jmp.arg);
- assert(l != Top && "ssa invariant broken");
if (l == Bot) {
edge[n][1].work = flowrk;
edge[n][0].work = &edge[n][1];
@@ -174,7 +173,6 @@ renref(Ref *r)
if (rtype(*r) == RTmp)
if ((l=val[r->val]) != Bot) {
- assert(l != Top && "ssa invariant broken");
*r = CON(l);
return 1;
}
@@ -294,9 +292,13 @@ fold(Fn *fn)
for (i=b->ins; i<&b->ins[b->nins]; i++)
if (renref(&i->to))
*i = (Ins){.op = Onop};
- else
+ else {
for (n=0; n<2; n++)
renref(&i->arg[n]);
+ if (isstore(i->op))
+ if (req(i->arg[0], UNDEF))
+ *i = (Ins){.op = Onop};
+ }
renref(&b->jmp.arg);
if (b->jmp.type == Jjnz && rtype(b->jmp.arg) == RCon) {
if (iscon(&fn->con[b->jmp.arg.val], 0, 0)) {
diff --git a/mem.c b/mem.c
@@ -201,7 +201,7 @@ coalesce(Fn *fn)
Ref *arg;
bits x;
int64_t off0, off1;
- int n, m, sz, nsl, nbl, ip, *stk;
+ int n, m, ip, sz, nsl, nbl, *stk;
uint total, freed, fused;
/* minimize the stack usage
@@ -317,26 +317,31 @@ coalesce(Fn *fn)
while (n--) {
t = &fn->tmp[stk[n]];
assert(t->ndef == 1 && t->def);
- *t->def = (Ins){.op = Onop};
+ i = t->def;
+ if (isload(i->op)) {
+ i->op = Ocopy;
+ i->arg[0] = UNDEF;
+ continue;
+ }
+ *i = (Ins){.op = Onop};
for (u=t->use; u<&t->use[t->nuse]; u++) {
if (u->type == UJmp) {
b = fn->rpo[u->bid];
- b->jmp.arg = CON_Z;
+ assert(isret(b->jmp.type));
+ b->jmp.type = Jret0;
+ b->jmp.arg = R;
continue;
}
assert(u->type == UIns);
i = u->u.ins;
- /* make loads crash */
- if (isload(i->op))
- i->arg[0] = CON_Z;
- else if (i->op == Oargc)
- i->arg[1] = CON_Z;
- else if (!req(i->to, R)) {
+ if (!req(i->to, R)) {
assert(rtype(i->to) == RTmp);
vgrow(&stk, ++n);
stk[n-1] = i->to.val;
+ } else if (isarg(i->op)) {
+ assert(i->op == Oargc);
+ i->arg[1] = CON_Z; /* crash */
} else {
- assert(!isarg(i->op));
if (i->op == Oblit0)
*(i+1) = (Ins){.op = Onop};
*i = (Ins){.op = Onop};
diff --git a/parse.c b/parse.c
@@ -867,7 +867,7 @@ parsefn(Lnk *lnk)
curi = insb;
curf = alloc(sizeof *curf);
curf->ntmp = 0;
- curf->ncon = 1; /* first constant must be 0 */
+ curf->ncon = 2;
curf->tmp = vnew(curf->ntmp, sizeof curf->tmp[0], PFn);
curf->con = vnew(curf->ncon, sizeof curf->con[0], PFn);
for (i=0; i<Tmp0; ++i)
@@ -876,6 +876,8 @@ parsefn(Lnk *lnk)
else
newtmp(0, Kl, curf);
curf->con[0].type = CBits;
+ curf->con[0].bits.i = 0xdeaddead; /* UNDEF */
+ curf->con[1].type = CBits;
curf->lnk = *lnk;
blink = &curf->start;
curf->retty = Kx;
@@ -1230,7 +1232,10 @@ printref(Ref r, Fn *fn, FILE *f)
fprintf(f, "%%%s", fn->tmp[r.val].name);
break;
case RCon:
- printcon(&fn->con[r.val], f);
+ if (req(r, UNDEF))
+ fprintf(f, "UNDEF");
+ else
+ printcon(&fn->con[r.val], f);
break;
case RSlot:
fprintf(f, "S%d", rsval(r));
diff --git a/ssa.c b/ssa.c
@@ -264,7 +264,7 @@ getstk(int t, Blk *b, Name **stk)
stk[t] = n;
if (!n) {
/* uh, oh, warn */
- return CON_Z;
+ return UNDEF;
} else
return n->r;
}
diff --git a/util.c b/util.c
@@ -361,7 +361,7 @@ newcon(Con *c0, Fn *fn)
Con *c1;
int i;
- for (i=0; i<fn->ncon; i++) {
+ for (i=1; i<fn->ncon; i++) {
c1 = &fn->con[i];
if (c0->type == c1->type
&& symeq(c0->sym, c1->sym)
@@ -378,8 +378,9 @@ getcon(int64_t val, Fn *fn)
{
int c;
- for (c=0; c<fn->ncon; c++)
- if (fn->con[c].type == CBits && fn->con[c].bits.i == val)
+ for (c=1; c<fn->ncon; c++)
+ if (fn->con[c].type == CBits
+ && fn->con[c].bits.i == val)
return CON(c);
vgrow(&fn->con, ++fn->ncon);
fn->con[c] = (Con){.type = CBits, .bits.i = val};
