From 946d5854c0b2e63a3757a0fbdf41276255967bc8 Mon Sep 17 00:00:00 2001
From: Eddie Hung <eddie@fpgeh.com>
Date: Fri, 6 Dec 2019 17:27:47 -0800
Subject: [PATCH] Drop keep=0 attributes on SB_CARRY

---
 passes/pmgen/ice40_wrapcarry.cc | 8 ++++++++
 tests/arch/ice40/wrapcarry.ys   | 4 ++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/passes/pmgen/ice40_wrapcarry.cc b/passes/pmgen/ice40_wrapcarry.cc
index b84790d8f..8b3cf38bb 100644
--- a/passes/pmgen/ice40_wrapcarry.cc
+++ b/passes/pmgen/ice40_wrapcarry.cc
@@ -51,6 +51,9 @@ void create_ice40_wrapcarry(ice40_wrapcarry_pm &pm)
 	cell->setParam("\\LUT", st.lut->getParam("\\LUT_INIT"));
 
 	cell->attributes = std::move(st.carry->attributes);
+	auto it = cell->attributes.find(ID::keep);
+	if (it != cell->attributes.end() && !it->second.as_bool())
+		cell->attributes.erase(it);
 	cell->attributes.insert(st.lut->attributes.begin(), st.lut->attributes.end());
 
 	pm.autoremove(st.carry);
@@ -69,6 +72,11 @@ struct Ice40WrapCarryPass : public Pass {
 		log("into an internal $__ICE40_CARRY_WRAPPER cell for preservation across technology\n");
 		log("mapping.");
 		log("\n");
+		log("Attributes on both cells will be merged, with SB_CARRY attributes having priority\n");
+		log("over SB_LUT4 attributes, except when (* keep *) attributes present on the SB_CARRY4\n");
+		log("that logically evaluate to false will be dropped (thus allowing the keep attribute,\n");
+		log("if any, on the SB_LUT4 to be adopted).\n");
+		log("\n");
 	}
 	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
diff --git a/tests/arch/ice40/wrapcarry.ys b/tests/arch/ice40/wrapcarry.ys
index a4b0d357a..579335b27 100644
--- a/tests/arch/ice40/wrapcarry.ys
+++ b/tests/arch/ice40/wrapcarry.ys
@@ -24,7 +24,7 @@ select -assert-count 1 t:$__ICE40_CARRY_WRAPPER
 design -reset
 read_verilog <<EOT
 module top(input A, B, CI, output O, CO);
-    (* foo = "bar", answer = 42 *)
+    (* foo = "bar", answer = 42, keep=0 *)
 	SB_CARRY carry (
 		.I0(A),
 		.I1(B),
@@ -47,6 +47,6 @@ EOT
 ice40_wrapcarry
 select -assert-count 1 t:$__ICE40_CARRY_WRAPPER
 select -assert-count 0 t:* t:$__ICE40_CARRY_WRAPPER %d
-select -assert-count 1 a:foo=bar a:answer=42 %i a:keep %i a:blah=blah %i
+select -assert-count 1 a:foo=bar a:answer=42 %i a:keep=1 %i a:blah=blah %i
 techmap -map +/ice40/cells_map.v
 #TODO: Check unwrapped attributes