From 256aa3e389e325b925e554d1d3b52abaac2c7a11 Mon Sep 17 00:00:00 2001
From: Jannis Harder <me@jix.one>
Date: Tue, 12 Aug 2025 14:38:20 +0200
Subject: [PATCH] check: Limit detailed cell edge checking for $pmux and $bmux

While these cells can't have a quadratic number of edges between A, B
and Y, they do have a quadratic number of edges between S and Y.
---
 passes/cmds/check.cc | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/passes/cmds/check.cc b/passes/cmds/check.cc
index 8bbcb8da0..3017630a6 100644
--- a/passes/cmds/check.cc
+++ b/passes/cmds/check.cc
@@ -195,16 +195,23 @@ struct CheckPass : public Pass {
 					// in port widths are those for us to check.
 					if (!cell->type.in(
 							ID($add), ID($sub),
-							ID($shl), ID($shr), ID($sshl), ID($sshr), ID($shift), ID($shiftx)))
+							ID($shl), ID($shr), ID($sshl), ID($sshr), ID($shift), ID($shiftx),
+							ID($pmux), ID($bmux)))
 						return false;
 
 					int in_widths = 0, out_widths = 0;
 
-					for (auto &conn : cell->connections()) {
-						if (cell->input(conn.first))
-							in_widths += conn.second.size();
-						if (cell->output(conn.first))
-							out_widths += conn.second.size();
+					if (cell->type.in(ID($pmux), ID($bmux))) {
+						// We're skipping inputs A and B, since each of their bits contributes only one edge
+						in_widths = GetSize(cell->getPort(ID::S));
+						out_widths = GetSize(cell->getPort(ID::Y));
+					} else {
+						for (auto &conn : cell->connections()) {
+							if (cell->input(conn.first))
+								in_widths += conn.second.size();
+							if (cell->output(conn.first))
+								out_widths += conn.second.size();
+						}
 					}
 
 					const int threshold = 1024;