From 6b3208b522d80467dcde5da5034a89a74cd07f39 Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Thu, 28 Jul 2022 18:42:50 +0100
Subject: [PATCH] Lowering for 'STABLE and 'QUIET attributes. Issue #495

---
 src/lower.c                | 29 +++++++++++++++++++++++++++++
 test/regress/implicit4.vhd | 33 +++++++++++++++++++++++++++++++++
 test/regress/testlist.txt  |  1 +
 3 files changed, 63 insertions(+)
 create mode 100644 test/regress/implicit4.vhd

diff --git a/src/lower.c b/src/lower.c
index 98c6d4a1..ea063972 100644
--- a/src/lower.c
+++ b/src/lower.c
@@ -4001,6 +4001,35 @@ static vcode_reg_t lower_attr_ref(tree_t expr, expr_ctx_t ctx)
          return emit_cast(lower_type(type), lower_bounds(type), arg);
       }
 
+   case ATTR_STABLE:
+   case ATTR_QUIET:
+      {
+         tree_t param = tree_value(tree_param(expr, 0));
+         vcode_reg_t param_reg = lower_param(param, NULL, PORT_IN);
+
+         type_t name_type = tree_type(name);
+         vcode_reg_t name_reg = lower_expr(name, EXPR_LVALUE), len_reg;
+         if (type_is_array(name_type)) {
+            len_reg = lower_array_total_len(name_type, name_reg);
+            name_reg = lower_array_data(name_reg);
+         }
+         else
+            len_reg = emit_const(vtype_offset(), 1);
+
+         vcode_reg_t flag_reg, time_reg;
+         if (predef == ATTR_STABLE) {
+            time_reg = emit_last_event(name_reg, len_reg);
+            flag_reg = emit_event_flag(name_reg, len_reg);
+         }
+         else {
+            time_reg = emit_last_active(name_reg, len_reg);
+            flag_reg = emit_active_flag(name_reg, len_reg);
+         }
+
+         vcode_reg_t cmp_reg = emit_cmp(VCODE_CMP_GEQ, time_reg, param_reg);
+         return emit_and(cmp_reg, emit_not(flag_reg));
+      }
+
    default:
       fatal_at(tree_loc(expr), "cannot lower attribute %s (%d)",
                istr(tree_ident(expr)), predef);
diff --git a/test/regress/implicit4.vhd b/test/regress/implicit4.vhd
new file mode 100644
index 00000000..7b868f31
--- /dev/null
+++ b/test/regress/implicit4.vhd
@@ -0,0 +1,33 @@
+entity implicit4 is
+end entity;
+
+architecture test of implicit4 is
+    signal x : integer;
+begin
+
+    p1: process is
+    begin
+        assert x'stable;
+        assert x'quiet;
+        assert x'stable(1 hr);
+        assert x'quiet(1 hr);
+        x <= 4;
+        wait for 0 ns;
+        assert not x'stable;
+        assert not x'quiet;
+        wait for 0 ns;
+        assert x'stable;
+        assert x'quiet;
+        assert not x'stable(1 ns);
+        assert not x'quiet(1 ns);
+        wait for 1 ns;
+        assert x'stable(1 ns);
+        assert x'quiet(1 ns);
+        x <= 4;
+        wait for 0 ns;
+        assert x'stable;
+        assert not x'quiet;
+        wait;
+    end process;
+
+end architecture;
diff --git a/test/regress/testlist.txt b/test/regress/testlist.txt
index 415df2ce..9419aaa5 100644
--- a/test/regress/testlist.txt
+++ b/test/regress/testlist.txt
@@ -634,3 +634,4 @@ issue493        shell
 issue494        fail,gold
 record36        normal,2008
 issue497        normal,2008
+implicit4       normal
-- 
2.39.2