From: Eddie Hung <eddie@fpgeh.com>
Date: Thu, 19 Mar 2020 21:34:10 +0000 (-0700)
Subject: opt_expr: optimise $sub when both A[i] and B[i] == 1'b1
X-Git-Tag: working-ls180~709^2~2
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=213a89558;p=yosys.git

opt_expr: optimise $sub when both A[i] and B[i] == 1'b1
---

diff --git a/passes/opt/opt_expr.cc b/passes/opt/opt_expr.cc
index 94084bf62..c818fefc5 100644
--- a/passes/opt/opt_expr.cc
+++ b/passes/opt/opt_expr.cc
@@ -651,10 +651,14 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 				int i;
 				for (i = 0; i < GetSize(sig_y); i++) {
-					if (sig_b.at(i, State::Sx) == State::S0 && sig_a.at(i, State::Sx) != State::Sx)
-						module->connect(sig_y[i], sig_a[i]);
-					else if (!sub && sig_a.at(i, State::Sx) == State::S0 && sig_b.at(i, State::Sx) != State::Sx)
-						module->connect(sig_y[i], sig_b[i]);
+					RTLIL::SigBit b = sig_b.at(i, State::Sx);
+					RTLIL::SigBit a = sig_a.at(i, State::Sx);
+					if (b == State::S0 && a != State::Sx)
+						module->connect(sig_y[i], a);
+					else if (sub && b == State::S1 && a == State::S1)
+						module->connect(sig_y[i], State::S0);
+					else if (!sub && a == State::S0 && b != State::Sx)
+						module->connect(sig_y[i], b);
 					else
 						break;
 				}
@@ -690,14 +694,21 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 				int i;
 				for (i = 0; i < GetSize(sig_y); i++) {
-					if (sig_b.at(i, State::Sx) == State::S0 && sig_a.at(i, State::Sx) != State::Sx) {
-						module->connect(sig_x[i], sub ? module->Not(NEW_ID, sig_a[i]).as_bit() : sig_a[i]);
+					RTLIL::SigBit b = sig_b.at(i, State::Sx);
+					RTLIL::SigBit a = sig_a.at(i, State::Sx);
+					if (b == State::S0 && a != State::Sx) {
 						module->connect(sig_y[i], sig_a[i]);
+						module->connect(sig_x[i], sub ? module->Not(NEW_ID, a).as_bit() : a);
 						module->connect(sig_co[i], sub ? State::S1 : State::S0);
 					}
-					else if (!sub && sig_a.at(i, State::Sx) == State::S0 && sig_b.at(i, State::Sx) != State::Sx) {
-						module->connect(sig_x[i], sig_b[i]);
-						module->connect(sig_y[i], sig_b[i]);
+					else if (sub && b == State::S1 && a == State::S1) {
+						module->connect(sig_y[i], State::S0);
+						module->connect(sig_x[i], module->Not(NEW_ID, a));
+						module->connect(sig_co[i], State::S0);
+					}
+					else if (!sub && a == State::S0 && b != State::Sx) {
+						module->connect(sig_y[i], b);
+						module->connect(sig_x[i], b);
 						module->connect(sig_co[i], State::S0);
 					}
 					else