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-rw-r--r--passes/opt/opt_const.cc8
1 files changed, 6 insertions, 2 deletions
diff --git a/passes/opt/opt_const.cc b/passes/opt/opt_const.cc
index 1e9b1331..aa376ae0 100644
--- a/passes/opt/opt_const.cc
+++ b/passes/opt/opt_const.cc
@@ -242,11 +242,15 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module)
FOLD_1ARG_CELL(pos)
FOLD_1ARG_CELL(neg)
+ // be very conservative with optimizing $mux cells as we do not want to break mux trees
if (cell->type == "$mux") {
- RTLIL::SigSpec input = cell->connections["\\S"];
- assign_map.apply(input);
+ RTLIL::SigSpec input = assign_map(cell->connections["\\S"]);
+ RTLIL::SigSpec inA = assign_map(cell->connections["\\A"]);
+ RTLIL::SigSpec inB = assign_map(cell->connections["\\B"]);
if (input.is_fully_const())
ACTION_DO("\\Y", input.as_bool() ? cell->connections["\\B"] : cell->connections["\\A"]);
+ else if (inA == inB)
+ ACTION_DO("\\Y", cell->connections["\\A"]);
}
next_cell:;