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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 dce.cc
/// @brief Dead Code Elimination: mark-and-sweep starting from side-effect / control flow roots.
///
/// See docs/dce.md for architectural notes.
#include "rcc/all.h"
#include <vector>
namespace rcc {
namespace {
bool is_root(uint op) {
if (isstore(op))
return true;
if (isalloc(op))
return true;
if (ispar(op))
return true;
if (isarg(op))
return true;
if (op == Ocall)
return true;
if (op == Oblit0 || op == Oblit1)
return true;
if (op == Ovastart || op == Ovaarg)
return true;
if (op == Odbgloc)
return true;
if (op == Osel0 || op == Osel1)
return true;
return false;
}
} // namespace
void dce(Ctx*, Fn* fn) {
int ntmp = fn->ntmp;
std::vector<Phi*> phi_def(static_cast<size_t>(ntmp), nullptr);
std::vector<Ins*> ins_def(static_cast<size_t>(ntmp), nullptr);
for (Blk* b = fn->start; b; b = b->link) {
for (Phi* p = b->phi; p; p = p->link)
if (rtype(p->to) == RTmp && p->to.val < static_cast<uint>(ntmp))
phi_def[p->to.val] = p;
for (uint k = 0; k < b->nins; k++) {
Ins* i = &b->ins[k];
if (rtype(i->to) == RTmp && i->to.val < static_cast<uint>(ntmp))
ins_def[i->to.val] = i;
}
}
std::vector<char> alive(static_cast<size_t>(ntmp), 0);
std::vector<uint> wl;
auto mark = [&](Ref r) {
if (rtype(r) == RTmp && r.val < static_cast<uint>(ntmp) && !alive[r.val]) {
alive[r.val] = 1;
wl.push_back(r.val);
}
};
for (Blk* b = fn->start; b; b = b->link) {
for (uint k = 0; k < b->nins; k++) {
Ins* i = &b->ins[k];
if (is_root(i->op)) {
mark(i->arg[0]);
mark(i->arg[1]);
}
}
mark(b->jmp.arg);
}
while (!wl.empty()) {
uint t = wl.back();
wl.pop_back();
if (Ins* d = ins_def[t]) {
mark(d->arg[0]);
mark(d->arg[1]);
continue;
}
if (Phi* p = phi_def[t]) {
for (uint a = 0; a < p->narg; a++)
mark(p->arg[a]);
}
}
int killed_ins = 0, killed_phi = 0;
for (Blk* b = fn->start; b; b = b->link) {
Phi** pp = &b->phi;
while (*pp) {
Phi* p = *pp;
bool dead =
(rtype(p->to) == RTmp && p->to.val < static_cast<uint>(ntmp) && !alive[p->to.val]);
if (dead) {
*pp = p->link;
killed_phi++;
} else {
pp = &p->link;
}
}
uint w = 0;
for (uint k = 0; k < b->nins; k++) {
Ins* i = &b->ins[k];
if (i->op == Onop) {
killed_ins++;
continue;
}
bool root = is_root(i->op);
bool has_to = (rtype(i->to) == RTmp && i->to.val < static_cast<uint>(ntmp));
if (!root && has_to && !alive[i->to.val]) {
killed_ins++;
continue;
}
if (w != k)
b->ins[w] = *i;
w++;
}
b->nins = w;
}
if (debug['D']) {
fprintf(stderr, "\n> DCE for %s: killed %d ins, %d phi\n", fn->name, killed_ins,
killed_phi);
}
}
} // namespace rcc
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