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Akash Levy 2026-03-30 17:31:59 -07:00 committed by GitHub
parent df43a3097a
commit db1e0701b0
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1 changed files with 8 additions and 1 deletions
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9
passes/silimate/negopt.cc
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@ -24,7 +24,13 @@ PRIVATE_NAMESPACE_BEGIN
bool did_something;
// Normalize top-end sign/zero extension for PMG prefiltering
// Normalize top-end sign/zero extension for PMG prefiltering.
// Strips any redundant high bits so that a sign- or zero-extended SigSpec
// and its narrower original compare equal under index lookups.
// - top == prev: sign extension (MSB replicated)
// - top == SigBit(State::S0): zero extension (constant-zero padding)
// Only the prefilter key is stripped; exact legality is re-checked in the
// code block, so false-positive index hits are safe.
static SigSpec strip_ext_for_match(SigSpec sig)
{
int n = GetSize(sig);
@ -34,6 +40,7 @@ static SigSpec strip_ext_for_match(SigSpec sig)
while (n > 1) {
SigBit top = sig[n-1];
SigBit prev = sig[n-2];
// Strip sign-extended (repeated MSB) or zero-extended (S0) bits
if (top == prev || top == SigBit(State::S0)) {
n--;
continue;