From 379f33af5489850ef8e2e58ef12ff5b22da87711 Mon Sep 17 00:00:00 2001
From: Eddie Hung <eddie@fpgeh.com>
Date: Thu, 22 Aug 2019 08:22:23 -0700
Subject: [PATCH] Handle $shift and Y_WIDTH > 1 as per @cliffordwolf

---
 passes/opt/opt_expr.cc | 12 ++++++++----
 tests/opt/opt_expr.ys  | 44 +++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/passes/opt/opt_expr.cc b/passes/opt/opt_expr.cc
index aca15e5f2..c4da613ab 100644
--- a/passes/opt/opt_expr.cc
+++ b/passes/opt/opt_expr.cc
@@ -745,16 +745,20 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
-		if (cell->type == ID($shiftx) && GetSize(cell->getPort(ID::Y)) == 1) {
+		if (cell->type.in(ID($shiftx), ID($shift))) {
 			SigSpec sig_a = assign_map(cell->getPort(ID::A));
 			int width;
+			bool trim_x = true;
+			bool trim_0 = cell->type == ID($shift);
 			for (width = GetSize(sig_a); width > 1; width--) {
-				if (sig_a[width-1] != State::Sx)
-					break;
+				if ((trim_x && sig_a[width-1] == State::Sx) ||
+					(trim_0 && sig_a[width-1] == State::S0))
+					continue;
+				break;
 			}
 
 			if (width < GetSize(sig_a)) {
-				cover("opt.opt_expr.trim_shiftx");
+				cover_list("opt.opt_expr.xbit", "$shiftx", "$shift", cell->type.str());
 				sig_a.remove(width, GetSize(sig_a)-width);
 				cell->setPort(ID::A, sig_a);
 				cell->setParam(ID(A_WIDTH), width);
diff --git a/tests/opt/opt_expr.ys b/tests/opt/opt_expr.ys
index 4affc1ac8..02be20a62 100644
--- a/tests/opt/opt_expr.ys
+++ b/tests/opt/opt_expr.ys
@@ -226,7 +226,7 @@ select -assert-count 1 t:$alu r:A_WIDTH=8 r:B_WIDTH=8 r:Y_WIDTH=9 %i %i %i
 
 design -reset
 read_verilog -icells <<EOT
-module opt_expr_shiftx(input [2:0] a, input [1:0] b, output y);
+module opt_expr_shiftx_1bit(input [2:0] a, input [1:0] b, output y);
     \$shiftx #(.A_SIGNED(0), .B_SIGNED(0), .A_WIDTH(4), .B_WIDTH(2), .Y_WIDTH(1)) shiftx (.A({1'bx,a}), .B(b), .Y(y));
 endmodule
 EOT
@@ -235,3 +235,45 @@ check
 equiv_opt opt_expr
 design -load postopt
 select -assert-count 1 t:$shiftx r:A_WIDTH=3 %i
+
+###########
+
+design -reset
+read_verilog -icells <<EOT
+module opt_expr_shiftx_3bit(input [9:0] a, input [3:0] b, output [2:0] y);
+    \$shiftx #(.A_SIGNED(0), .B_SIGNED(0), .A_WIDTH(14), .B_WIDTH(4), .Y_WIDTH(3)) shiftx (.A({4'bxx00,a}), .B(b), .Y(y));
+endmodule
+EOT
+check
+
+equiv_opt opt_expr
+design -load postopt
+select -assert-count 1 t:$shiftx r:A_WIDTH=12 %i
+
+###########
+
+design -reset
+read_verilog -icells <<EOT
+module opt_expr_shift_1bit(input [2:0] a, input [1:0] b, output y);
+    \$shift #(.A_SIGNED(0), .B_SIGNED(0), .A_WIDTH(4), .B_WIDTH(2), .Y_WIDTH(1)) shift (.A({1'b0,a}), .B(b), .Y(y));
+endmodule
+EOT
+check
+
+equiv_opt opt_expr
+design -load postopt
+select -assert-count 1 t:$shift r:A_WIDTH=3 %i
+
+###########
+
+design -reset
+read_verilog -icells <<EOT
+module opt_expr_shift_3bit(input [9:0] a, input [3:0] b, output [2:0] y);
+    \$shift #(.A_SIGNED(0), .B_SIGNED(0), .A_WIDTH(14), .B_WIDTH(4), .Y_WIDTH(3)) shift (.A({4'b0x0x,a}), .B(b), .Y(y));
+endmodule
+EOT
+check
+
+equiv_opt opt_expr
+design -load postopt
+select -assert-count 1 t:$shift r:A_WIDTH=10 %i
-- 
2.30.2