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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 peephole.cc
/// @brief Backend sliding-window peephole pass.
#include "rcc/all.h"
namespace rcc {
namespace {
// Store op to byte width.
int store_size(int op) {
switch (op) {
case Ostoreb:
return 1;
case Ostoreh:
return 2;
case Ostorew:
case Ostores:
return 4;
case Ostorel:
case Ostored:
return 8;
default:
return 0;
}
}
// Check if store and load are compatible for forwarding.
bool store_load_compatible(int sop, int lcls) {
switch (sop) {
case Ostorew:
return lcls == Kw;
case Ostorel:
return lcls == Kl;
case Ostores:
return lcls == Ks;
case Ostored:
return lcls == Kd;
default:
return false;
}
}
void peep_blk(Blk* b) {
uint n = b->nins;
if (n == 0)
return;
// Self Ocopy elimination.
for (uint k = 0; k < n; k++) {
Ins* i = &b->ins[k];
if (i->op == Ocopy && req(i->to, i->arg[0]) && rtype(i->to) != -1)
i->op = Onop;
}
// Window 2 mode.
auto next_live = [&](uint from) -> int {
for (uint k = from; k < n; k++)
if (b->ins[k].op != Onop)
return static_cast<int>(k);
return -1;
};
int p = next_live(0);
while (p >= 0) {
int q = next_live(static_cast<uint>(p) + 1);
if (q < 0)
break;
Ins* pi = &b->ins[p];
Ins* qi = &b->ins[q];
// Store + Load to same slot: keep store, change load to copy.
if (isstore(pi->op) && qi->op == Oload && rtype(pi->arg[1]) == RSlot &&
rtype(qi->arg[0]) == RSlot && req(pi->arg[1], qi->arg[0]) &&
store_load_compatible(pi->op, qi->cls) && rtype(pi->arg[0]) != RCon) {
// Skip forwarding if value is a constant.
qi->op = Ocopy;
qi->arg[0] = pi->arg[0];
qi->arg[1] = Ref::none();
// Keep cls and to.
p = q;
continue;
}
// Consecutive stores to same slot: drop first.
if (isstore(pi->op) && pi->op == qi->op && rtype(pi->arg[1]) == RSlot &&
rtype(qi->arg[1]) == RSlot && req(pi->arg[1], qi->arg[1]) && store_size(pi->op) > 0) {
pi->op = Onop;
p = q;
continue;
}
p = q;
}
// Redundant Oextsw elimination.
for (uint pidx = 0; pidx < n; pidx++) {
Ins* pi = &b->ins[pidx];
if (pi->op != Oextsw)
continue;
if (!isreg(pi->to) || !isreg(pi->arg[0]))
continue;
for (uint qidx = pidx + 1; qidx < n; qidx++) {
Ins* qi = &b->ins[qidx];
if (qi->op == Onop)
continue;
// Identical Oextsw.
if (qi->op == pi->op && req(qi->to, pi->to) && req(qi->arg[0], pi->arg[0]) &&
req(qi->arg[1], pi->arg[1])) {
qi->op = Onop;
continue;
}
// Anchor invalidated.
if (isreg(qi->to) && (req(qi->to, pi->to) || req(qi->to, pi->arg[0])))
break;
}
}
}
} // namespace
void peephole(Ctx* /*ctx*/, Fn* fn) {
for (Blk* b = fn->start; b; b = b->link)
peep_blk(b);
}
} // namespace rcc
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