From 7067f0d7885b57cd00ad62ee0ff776b554592ac0 Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Wed, 2 Dec 2020 21:39:25 +0000
Subject: [PATCH] cxxrtl: fix crashes caused by a floating or constant clock
 input.

E.g. in:

    module test;
        wire clk = 0;
        reg data;
        always @(posedge clk)
            data <= 0;
    endmodule
---
 backends/cxxrtl/cxxrtl_backend.cc | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/backends/cxxrtl/cxxrtl_backend.cc b/backends/cxxrtl/cxxrtl_backend.cc
index a48ea5b23..38d2efb84 100644
--- a/backends/cxxrtl/cxxrtl_backend.cc
+++ b/backends/cxxrtl/cxxrtl_backend.cc
@@ -1036,8 +1036,12 @@ struct CxxrtlWorker {
 				// Edge-sensitive logic
 				RTLIL::SigBit clk_bit = cell->getPort(ID::CLK)[0];
 				clk_bit = sigmaps[clk_bit.wire->module](clk_bit);
-				f << indent << "if (" << (cell->getParam(ID::CLK_POLARITY).as_bool() ? "posedge_" : "negedge_")
-				            << mangle(clk_bit) << ") {\n";
+				if (clk_bit.wire) {
+					f << indent << "if (" << (cell->getParam(ID::CLK_POLARITY).as_bool() ? "posedge_" : "negedge_")
+					            << mangle(clk_bit) << ") {\n";
+				} else {
+					f << indent << "if (false) {\n";
+				}
 				inc_indent();
 					if (cell->hasPort(ID::EN)) {
 						f << indent << "if (";
@@ -1130,8 +1134,12 @@ struct CxxrtlWorker {
 			if (cell->getParam(ID::CLK_ENABLE).as_bool()) {
 				RTLIL::SigBit clk_bit = cell->getPort(ID::CLK)[0];
 				clk_bit = sigmaps[clk_bit.wire->module](clk_bit);
-				f << indent << "if (" << (cell->getParam(ID::CLK_POLARITY).as_bool() ? "posedge_" : "negedge_")
-				            << mangle(clk_bit) << ") {\n";
+				if (clk_bit.wire) {
+					f << indent << "if (" << (cell->getParam(ID::CLK_POLARITY).as_bool() ? "posedge_" : "negedge_")
+					            << mangle(clk_bit) << ") {\n";
+				} else {
+					f << indent << "if (false) {\n";
+				}
 				inc_indent();
 			}
 			RTLIL::Memory *memory = cell->module->memories[cell->getParam(ID::MEMID).decode_string()];
@@ -2105,14 +2113,14 @@ struct CxxrtlWorker {
 
 				// Various DFF cells are treated like posedge/negedge processes, see above for details.
 				if (cell->type.in(ID($dff), ID($dffe), ID($adff), ID($adffe), ID($dffsr), ID($dffsre), ID($sdff), ID($sdffe), ID($sdffce))) {
-					if (cell->getPort(ID::CLK).is_wire())
+					if (sigmap(cell->getPort(ID::CLK)).is_wire())
 						register_edge_signal(sigmap, cell->getPort(ID::CLK),
 							cell->parameters[ID::CLK_POLARITY].as_bool() ? RTLIL::STp : RTLIL::STn);
 				}
 				// Similar for memory port cells.
 				if (cell->type.in(ID($memrd), ID($memwr))) {
 					if (cell->getParam(ID::CLK_ENABLE).as_bool()) {
-						if (cell->getPort(ID::CLK).is_wire())
+						if (sigmap(cell->getPort(ID::CLK)).is_wire())
 							register_edge_signal(sigmap, cell->getPort(ID::CLK),
 								cell->parameters[ID::CLK_POLARITY].as_bool() ? RTLIL::STp : RTLIL::STn);
 					}
-- 
2.30.2