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#include "ir.h"
static struct bitset globusage[1];
static struct bitset taken[1];
static void
def(struct instr *ins)
{
if (ins->reg)
bsclr(taken, ins->reg - 1);
}
static void
take(int r) {
bsset(taken, r);
bsset(globusage, r);
}
static int
nextreg(enum irclass cls)
{
int r0, rend, i;
assert(cls);
if (kisint(cls)) {
r0 = mctarg->gpr0;
rend = mctarg->gpr0 + mctarg->ngpr;
} else if (kisflt(cls)) {
r0 = mctarg->fpr0;
rend = mctarg->fpr0 + mctarg->nfpr;
} else assert(0);
for (i = r0; i < rend; ++i) {
if (!bstest(taken, i)) {
take(i);
return i;
}
}
assert(!"no more reg");
}
static void
use(struct block *blk, enum op op, int hint, union ref *ref)
{
struct instr *ins;
if (ref->t == RMORE) {
if (op == Ophi) {
struct phi *phi = &phitab.p[ref->i];
for (int i = 0; i < phi->n; ++i)
use(blk, 0, hint, &phi->ref[i]);
} else {
struct addr *addr = &addrtab.p[ref->i];
if (addr->base.t) use(blk, 0, hint, &addr->base);
if (addr->index.t) use(blk, 0, hint, &addr->index);
}
return;
} else if (ref->t != RTMP) return;
ins = &instrtab[ref->i];
if (oisalloca(ins->op)) return;
if (!ins->cls) return;
if (!ins->reg) {
if (op == -1) /* cond branch */
if (oiscmp(ins->op) && ref->i == blk->ins.p[blk->ins.n-1])
/* result of comparison instr is only used to conditionally branch,
* doesn't usually need a reg (handled by isel) */
return;
assert(ins->op != Ocall);
if (hint != -1 && !bstest(taken, hint)) {
take(hint);
ins->reg = hint + 1;
} else {
ins->reg = nextreg(ins->cls) + 1;
}
*ref = mkref(RREG, ins->reg-1);
}
}
void
regalloc(struct function *fn)
{
struct instr *ins;
struct block *last = fn->entry->lprev, *blk;
/* a dumb linear register allocator that visits instructions physically backwards
* starting at the end of the function, when encountering a use of a new
* temporary, it allocates a register for it. when encountering the definition
* of a temporary, it frees up its register
*/
blk = last;
do {
for (int i = 0; i < 2; ++i) {
if (!blk->jmp.arg[i].t) break;
use(blk, (blk->jmp.t == Jb) - 1,
blk->jmp.t == Jret ? fn->abiret[i].reg : -1,
&blk->jmp.arg[i]);
}
for (struct block *s = blk->s1; s; s = blk->s2) {
/* introduce necessary moves for successors' phis */
for (int i = 0; i < s->phi.n; ++i) {
ins = &instrtab[s->phi.p[i]];
struct phi *phi = &phitab.p[ins->l.i];
for (int i = 0; i < phi->n; ++i) {
if (phi->blk[i] == blk) {
union ref src = phi->ref[i];
int reg = ins->reg - 1;
assert(reg >= 0);
if (src.t != RTMP || instrtab[src.i].reg-1 != reg) /* not in the right register already */
insertinstr(blk, blk->ins.n,
(struct instr){Ocopy, ins->cls, reg+1, .l = src});
break;
}
}
}
if (s == blk->s2) break;
}
for (int i = blk->ins.n - 1; i >= 0; --i) {
int hint0 = -1, hint1 = -1;
ins = &instrtab[blk->ins.p[i]];
if (!ins->reg && ins->skip) { /* unused */
*ins = mkinstr(Onop, 0,);
continue;
}
def(ins);
if (ins->op == Omove) {
use(blk, ins->op, ins->l.i, &ins->r);
} else if (ins->op != Ocall) {
if (ins->op == Ocopy) hint0 = ins->reg - 1;
if (ins->l.t) use(blk, ins->op, hint0, &ins->l);
if (ins->r.t) use(blk, ins->op, hint1, &ins->r);
} else {
struct call *call = &calltab.p[ins->r.i];
use(blk, ins->op, hint0, &ins->l);
}
}
for (int i = blk->phi.n - 1; i >= 0; --i) {
ins = &instrtab[blk->phi.p[i]];
assert(ins->op == Ophi);
def(ins);
use(blk, Ophi, ins->reg - 1, &ins->l);
}
} while ((blk = blk->lprev) != last);
do vfree(&blk->phi); while ((blk = blk->lprev) != last);
if (ccopt.dbg.r) {
efmt("after regalloc:\n");
irdump(fn, fn->name);
}
bscopy(fn->regusage, globusage, 1);
}
/* vim:set ts=3 sw=3 expandtab: */
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