Description

SizeDownMove::downSizeGate() in src/rsz/src/SizeDownMove.cc (L327-347) calls checkMaxCapViolation() and checkMaxSlewViolation() to validate downsized cell candidates. However, both functions only check against a single timing corner, as noted by two explicit FIXMEs:
FIXME 1 : BaseMove::checkMaxCapViolation() at L840:

// FIXME: Can we update to consider multiple corners? output_port->capacitanceLimit(resizer_->max_, max_cap, cap_limit_exists);

FIXME 2 : SizeDownMove::downSizeGate() at L333:

// FIXME: Only applies to current corner if (checkMaxCapViolation(output_pins[i], output_port, output_caps[i])) {

Why this matters:

In multi-corner/multi-mode (MCMM) designs which are standard practice for advanced nodes a cell swap that passes cap/slew checks at the current analysis corner may violate limits at another corner. For example:

A slow corner may have a different (tighter) max_cap limit
Different PVT conditions change drive resistance, affecting slew
Without multi-corner checking, SizeDownMove can introduce violations that repair_design must later fix or worse, violations that slip through entirely if repair doesn't re-check all corners.

Suggested Solution

Update checkMaxCapViolation() and checkMaxSlewViolation() in BaseMove.cc to iterate over all timing corners:

1. checkMaxCapViolation() : Replace the single capacitanceLimit() call with a loop over all scenes:

bool BaseMove::checkMaxCapViolation(const sta::Pin* output_pin, sta::LibertyPort* output_port, float output_cap) { // Check across all corners instead of just one for (const sta::Scene* scene : *sta_->scenes()) { float max_cap; bool cap_limit_exists; sta_->findCapLimit(output_port, scene, resizer_->max_, max_cap, cap_limit_exists); if (cap_limit_exists && max_cap > 0.0 && output_cap > max_cap) { // ... existing debugPrint ... return true; } } return false; }

2. checkMaxSlewViolation() : Similarly update to use sta_->findSlewLimit() across all corners.

3. SizeDownMove::downSizeGate() : Update the output cap computation to also check across corners (currently uses a single scene parameter).

The multi-corner pattern already exists in RepairDesign::checkSlew() (L1233) which calls sta_->checkSlew() across sta_->scenes() this can serve as a reference implementation.

I would like to work on a PR for this. @precisionmoon @maliberty @eder-matheus please assign this to me.

Additional Context

Impact: QoR regression in MCMM designs unchecked violations in non-active corners may persist through the flow.