diff options
Diffstat (limited to 'fold.c')
| -rw-r--r-- | fold.c | 231 |
1 files changed, 231 insertions, 0 deletions
diff --git a/fold.c b/fold.c new file mode 100644 index 0000000..0ca68c3 --- /dev/null +++ b/fold.c @@ -0,0 +1,231 @@ +#include "all.h" + +enum { + Bot = -2, /* lattice bottom */ + Top = -1, /* lattice top */ +}; + +typedef struct Edge Edge; + +struct Edge { + int dest; + int dead; + Edge *work; +}; + +int evalop(int, int, int, int); + +static int *val; +static Edge *flowrk, (*edge)[2]; +static Use **usewrk; +static uint nuse; + +static int +czero(Con *c) +{ + return c->type == CBits && c->bits.i == 0; +} + +static int +latval(Ref r) +{ + switch (rtype(r)) { + case RTmp: + return val[r.val]; + case RCon: + return r.val; + case RType: + return Bot; + default: + die("unreachable"); + } +} + +static int +latmerge(int l, int r) +{ + if (l == Bot || r == Bot) + return Bot; + if (l == Top) + return r; + if (r == Top) + return l; + if (l == r) + return l; + return Bot; +} + +static void +update(int t, int v, Fn *fn) +{ + Tmp *tmp; + uint u; + + if (val[t] != v) { + tmp = &fn->tmp[t]; + for (u=0; u<tmp->nuse; u++) { + vgrow(usewrk, ++nuse); + usewrk[nuse-1] = &tmp->use[u]; + } + } +} + +static void +visitphi(Phi *p, int n, Fn *fn) +{ + int v, dead; + uint a; + + v = Top; + for (a=0; a<p->narg; a++) { + if (edge[n][0].dest == p->blk[a]->id) + dead = edge[n][0].dead; + else + dead = edge[n][1].dead; + if (!dead) + v = latmerge(v, latval(p->arg[a])); + } + assert(v != Top); + update(p->to.val, v, fn); +} + +static void +visitins(Ins *i, Fn *fn) +{ + int v, l, r; + + if (rtype(i->to) != RTmp) + return; + l = latval(i->arg[0]); + r = latval(i->arg[1]); + v = evalop(i->op, i->cls, l, r); + assert(v != Top); + update(i->to.val, v, fn); +} + +static void +visitjmp(Blk *b, int n, Fn *fn) +{ + int l; + + switch (b->jmp.type) { + case JJnz: + l = latval(b->jmp.arg); + if (l == Bot) { + edge[n][1].work = flowrk; + edge[n][0].work = &edge[n][1]; + flowrk = &edge[n][0]; + } + else if (czero(&fn->con[l])) { + assert(edge[n][0].dead); + edge[n][1].work = flowrk; + flowrk = &edge[n][1]; + } + else { + assert(edge[n][1].dead); + edge[n][0].work = flowrk; + flowrk = &edge[n][0]; + } + break; + case JJmp: + edge[n][0].work = flowrk; + flowrk = &edge[n][0]; + break; + default: + if (isret(b->jmp.type)) + break; + die("unreachable"); + } +} + +static void +initedge(Edge *e, Blk *s) +{ + if (s) + e->dest = s->id; + else + e->dest = -1; + e->dead = 1; + e->work = 0; +} + +/* require rpo, use, pred */ +void +fold(Fn *fn) +{ + Edge *e; + Use *u; + Blk *b; + Phi *p; + Ins *i; + int n; + + val = emalloc(fn->ntmp * sizeof val[0]); + edge = emalloc(fn->nblk * sizeof edge[0]); + usewrk = vnew(0, sizeof usewrk[0]); + + for (n=0; n<fn->ntmp; n++) + val[n] = Bot; + for (n=0; n<fn->nblk; n++) { + b = fn->rpo[n]; + b->visit = 0; + initedge(&edge[n][0], b->s1); + initedge(&edge[n][1], b->s2); + } + assert(fn->start->id == 0); + edge[0][0].work = &edge[0][1]; + flowrk = &edge[0][0]; + nuse = 0; + + /* 1. find out constants and dead cfg edges */ + for (;;) { + e = flowrk; + if (e) { + flowrk = e->work; + e->work = 0; + if (e->dest == -1 || !e->dead) + continue; + e->dead = 0; + n = e->dest; + b = fn->rpo[n]; + for (p=b->phi; p; p=p->link) + visitphi(p, n, fn); + if (b->visit == 0) { + for (i=b->ins; i-b->ins < b->nins; i++) + visitins(i, fn); + visitjmp(b, n, fn); + } + b->visit++; + assert(b->jmp.type != JJmp + || edge[n][0].dead != 0 + || flowrk == &edge[n][0]); + } + else if (nuse) { + u = usewrk[--nuse]; + if (u->type == UPhi) { + visitphi(u->u.phi, u->bid, fn); + continue; + } + if (b->visit == 0) + continue; + n = u->bid; + switch (u->type) { + case UIns: + visitins(u->u.ins, fn); + break; + case UJmp: + visitjmp(fn->rpo[n], n, fn); + break; + default: + die("unreachable"); + } + } + else + break; + } + + /* 2. trim dead code, replace constants */ + + free(val); + free(edge); +} |