From db5b76edc14649e82d87c258481a2b0a46b1c345 Mon Sep 17 00:00:00 2001
From: Krystine Sherwin <93062060+KrystalDelusion@users.noreply.github.com>
Date: Fri, 14 Feb 2025 13:28:24 +1300
Subject: [PATCH 1/2] Add test for shifting by INT_MAX

Currently resulting in CI failing on main during fsm checks which generate a circuit that simplifies to this.
---
 tests/opt/opt_expr_shr_int_max.ys | 9 +++++++++
 1 file changed, 9 insertions(+)
 create mode 100644 tests/opt/opt_expr_shr_int_max.ys

diff --git a/tests/opt/opt_expr_shr_int_max.ys b/tests/opt/opt_expr_shr_int_max.ys
new file mode 100644
index 000000000..5fb3c9d37
--- /dev/null
+++ b/tests/opt/opt_expr_shr_int_max.ys
@@ -0,0 +1,9 @@
+read_verilog << EOF
+module uut_00034(b, y);
+  input signed [30:0] b;
+  output [11:0] y = b >> ~31'b0; // shift by INT_MAX
+endmodule
+EOF
+
+# This should succeed, even with UBSAN halt_on_error
+opt_expr

From 4c728968a3cedb90dae206e34624d831997d1ecf Mon Sep 17 00:00:00 2001
From: Krystine Sherwin <93062060+KrystalDelusion@users.noreply.github.com>
Date: Fri, 14 Feb 2025 13:29:24 +1300
Subject: [PATCH 2/2] Fix runtime error on shr INT_MAX

---
 passes/opt/opt_expr.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/passes/opt/opt_expr.cc b/passes/opt/opt_expr.cc
index ac4a65156..62a0ffc48 100644
--- a/passes/opt/opt_expr.cc
+++ b/passes/opt/opt_expr.cc
@@ -1315,6 +1315,10 @@ skip_fine_alu:
 			RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
 			RTLIL::SigSpec sig_y(cell->type == ID($shiftx) ? RTLIL::State::Sx : RTLIL::State::S0, cell->getParam(ID::Y_WIDTH).as_int());
 
+			// Limit indexing to the size of a, which is behaviourally identical (result is all 0)
+			// and avoids integer overflow of i + shift_bits when e.g. ID::B == INT_MAX
+			shift_bits = min(shift_bits, GetSize(sig_a));
+
 			if (cell->type != ID($shiftx) && GetSize(sig_a) < GetSize(sig_y))
 				sig_a.extend_u0(GetSize(sig_y), cell->getParam(ID::A_SIGNED).as_bool());