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/* Source code for RCC-Legacy.
Copyright (C) 2026 Richard Qin
This file is part of RCC.
RCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
RCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
along with RCC; see the file LICENSE. If not see
<http://www.gnu.org/licenses/>. */
/// @file ifopt.cc
/// @brief If-conversion: collapses if-then[-else] diamond CFG into straight-line block + sel
/// instructions.
///
/// See docs/ifopt.md for architectural notes.
#include "rcc/all.h"
namespace rcc {
namespace {
enum {
MaxIns = 2,
MaxPhis = 2,
};
bool okbranch(Blk* b) {
int n = 0;
for (Ins* i = b->ins; i < &b->ins[b->nins]; ++i) {
if (i->op == Odbgloc)
continue;
if (pinned(i))
return false;
if (i->op != Onop)
++n;
}
return n <= MaxIns;
}
bool okjoin(Blk* b) {
int n = 0;
for (Phi* p = b->phi; p; p = p->link) {
if (KBASE(p->cls) != 0)
return false;
++n;
}
return n <= MaxPhis;
}
bool okgraph(Blk* ifb, Blk* thenb, Blk* elseb, Blk* joinb) {
assert(thenb != elseb);
return joinb->npred == 2 && okjoin(joinb) && (thenb == ifb || okbranch(thenb)) &&
(elseb == ifb || okbranch(elseb));
}
void convert(Ctx* ctx, Blk* ifb, Blk* thenb, Blk* elseb, Blk* joinb) {
Ins* ins = static_cast<Ins*>(vnew(ctx, 0, sizeof ins[0], PHeap));
uint nins = 0;
addbins(ctx, &ins, &nins, ifb);
if (thenb != ifb)
addbins(ctx, &ins, &nins, thenb);
if (elseb != ifb)
addbins(ctx, &ins, &nins, elseb);
assert(joinb->npred == 2);
Ins sel = {};
if (joinb->phi) {
sel.op = Osel0;
sel.cls = static_cast<uint>(Kw);
sel.arg[0] = ifb->jmp.arg;
addins(ctx, &ins, &nins, &sel);
}
sel = {};
sel.op = Osel1;
for (Phi* p = joinb->phi; p; p = p->link) {
sel.to = p->to;
sel.cls = static_cast<uint>(p->cls);
sel.arg[0] = phiarg(p, thenb);
sel.arg[1] = phiarg(p, elseb);
addins(ctx, &ins, &nins, &sel);
}
idup(ctx, ifb, ins, nins);
ifb->jmp.type = Jjmp;
ifb->jmp.arg = Ref::none();
ifb->s1 = joinb;
ifb->s2 = nullptr;
joinb->npred = 1;
joinb->pred[0] = ifb;
joinb->phi = nullptr;
vfree(ins);
}
} // namespace
void ifconvert(Ctx* ctx, Fn* fn) {
if (debug['K'])
fputs("\n> If-conversion:\n", ctx->dbg_buf);
Blk *thenb, *elseb, *joinb;
for (Blk* ifb = fn->start; ifb; ifb = ifb->link)
if (ifgraph(ifb, &thenb, &elseb, &joinb) && okgraph(ifb, thenb, elseb, joinb)) {
if (debug['K'])
fprintf(ctx->dbg_buf, " @%s -> @%s, @%s -> @%s\n", ifb->name, thenb->name,
elseb->name, joinb->name);
convert(ctx, ifb, thenb, elseb, joinb);
}
if (debug['K']) {
fprintf(ctx->dbg_buf, "\n> After if-conversion:\n");
printfn(fn, ctx->dbg_buf);
}
}
} // namespace rcc
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