From b08a8807044980b7906362848f62291ede50e696 Mon Sep 17 00:00:00 2001
From: Jannis Harder <me@jix.one>
Date: Sun, 29 Jan 2023 13:54:02 +0100
Subject: [PATCH] backends/rtlil: Do not shorten a value with z bits to 'x

---
 backends/rtlil/rtlil_backend.cc |  2 +-
 kernel/rtlil.cc                 | 11 +++++++++++
 kernel/rtlil.h                  |  1 +
 tests/various/rtlil_z_bits.ys   |  9 +++++++++
 4 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 tests/various/rtlil_z_bits.ys

diff --git a/backends/rtlil/rtlil_backend.cc b/backends/rtlil/rtlil_backend.cc
index 7c7e26a93..574eb3aaa 100644
--- a/backends/rtlil/rtlil_backend.cc
+++ b/backends/rtlil/rtlil_backend.cc
@@ -51,7 +51,7 @@ void RTLIL_BACKEND::dump_const(std::ostream &f, const RTLIL::Const &data, int wi
 			}
 		}
 		f << stringf("%d'", width);
-		if (data.is_fully_undef()) {
+		if (data.is_fully_undef_x_only()) {
 			f << "x";
 		} else {
 			for (int i = offset+width-1; i >= offset; i--) {
diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index eee014c54..7f3508b2f 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -370,6 +370,17 @@ bool RTLIL::Const::is_fully_undef() const
 	return true;
 }
 
+bool RTLIL::Const::is_fully_undef_x_only() const
+{
+	cover("kernel.rtlil.const.is_fully_undef_x_only");
+
+	for (const auto &bit : bits)
+		if (bit != RTLIL::State::Sx)
+			return false;
+
+	return true;
+}
+
 bool RTLIL::Const::is_onehot(int *pos) const
 {
 	cover("kernel.rtlil.const.is_onehot");
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index 42bb66da8..7c7669caa 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -686,6 +686,7 @@ struct RTLIL::Const
 	bool is_fully_ones() const;
 	bool is_fully_def() const;
 	bool is_fully_undef() const;
+	bool is_fully_undef_x_only() const;
 	bool is_onehot(int *pos = nullptr) const;
 
 	inline RTLIL::Const extract(int offset, int len = 1, RTLIL::State padding = RTLIL::State::S0) const {
diff --git a/tests/various/rtlil_z_bits.ys b/tests/various/rtlil_z_bits.ys
new file mode 100644
index 000000000..c38669159
--- /dev/null
+++ b/tests/various/rtlil_z_bits.ys
@@ -0,0 +1,9 @@
+! mkdir -p temp
+read_rtlil <<EOT
+module \test
+  wire output 1 \a
+  connect \a 1'z
+end
+EOT
+write_rtlil temp/rtlil_z_bits.il
+! grep -F -q "connect \\a 1'z" temp/rtlil_z_bits.il