From 7ec740b7ad4ee4bc02e2564671e0153cdd08152f Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Fri, 7 Dec 2018 17:13:52 +0000
Subject: opt_lut: leave intact LUTs with cascade feeding module outputs.

---
 passes/opt/opt_lut.cc | 6 ++++++
 1 file changed, 6 insertions(+)

(limited to 'passes/opt')

diff --git a/passes/opt/opt_lut.cc b/passes/opt/opt_lut.cc
index 4207fbdb9..ba2cc6ee7 100644
--- a/passes/opt/opt_lut.cc
+++ b/passes/opt/opt_lut.cc
@@ -225,6 +225,12 @@ struct OptLutWorker
 
 					log("Found %s.%s (cell A) feeding %s.%s (cell B).\n", log_id(module), log_id(lutA), log_id(module), log_id(lutB));
 
+					if (index.query_is_output(lutA->getPort("\\Y")))
+					{
+						log("  Not combining LUTs (cascade connection feeds module output).\n");
+						continue;
+					}
+
 					pool<SigBit> lutA_inputs;
 					pool<SigBit> lutB_inputs;
 					for (auto &bit : lutA_input)
-- 
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