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Small update

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This commit is contained in:
Akash Levy 2026-06-18 05:26:28 -07:00
parent db7cfd404d
commit fe9689eaaf
1 changed files with 24 additions and 4 deletions
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28
passes/silimate/opt_carry_select.cc
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@ -194,20 +194,40 @@ struct OptCarrySelectWorker {
int narrow_w = std::min(a_w, b_w);
int k = narrow_w;
// Per-candidate trace (only wide adders, to keep -g output readable) so it
// is easy to see why a given $add was/was not turned into carry-select form.
bool show = w >= 32;
auto reject = [&](const char *why) {
if (show)
log_debug("opt_carry_select: %s/%s reject(%s) a_w=%d b_w=%d y_w=%d k=%d\n",
log_id(module), log_id(c), why, a_w, b_w, w, k);
return false;
};
if (k < 1 || k >= w)
return false;
return reject("narrow-not-narrower");
if (k > max_narrow)
return false;
return reject("narrow-too-wide");
if (w - k < min_wide)
return false;
return reject("high-too-small");
SigSpec wide_sig = c->getPort(wide_is_a ? ID::A : ID::B);
SigSpec narrow_sig = c->getPort(wide_is_a ? ID::B : ID::A);
double arr_wide = arrival(wide_sig);
double arr_narrow = arrival(narrow_sig);
if (arr_narrow <= arr_wide + margin)
if (arr_narrow <= arr_wide + margin) {
if (show)
log_debug("opt_carry_select: %s/%s reject(narrow-not-late) a_w=%d b_w=%d "
"y_w=%d k=%d arr_wide=%.2f arr_narrow=%.2f\n",
log_id(module), log_id(c), a_w, b_w, w, k, arr_wide, arr_narrow);
return false; // no timing benefit: narrow operand is not the late one
}
if (show)
log_debug("opt_carry_select: %s/%s accept a_w=%d b_w=%d y_w=%d k=%d "
"arr_wide=%.2f arr_narrow=%.2f\n",
log_id(module), log_id(c), a_w, b_w, w, k, arr_wide, arr_narrow);
plan.add = c;
plan.wide_is_a = wide_is_a;