grt: add unit test for parasitics estimation during guides restore

src/grt/test/BUILD

@@ -34,6 +34,7 @@ TESTS = [
     "gcd_cugr",
     "gcd_flute",
     "increase_capacity1",
+    "incremental_restore_vias",
     "incremental_update_net",
     "infinite_cap",
     "inst_pin_out_of_die",

src/grt/test/CMakeLists.txt

@@ -31,6 +31,7 @@ or_integration_tests(
     gcd_cugr
     gcd_flute
     increase_capacity1
+    incremental_restore_vias
     incremental_update_net
     infinite_cap
     inst_pin_out_of_die

src/grt/test/incremental_restore_vias.ok

@@ -0,0 +1,8 @@
+[INFO ODB-0227] LEF file: Nangate45/Nangate45.lef, created 22 layers, 27 vias, 135 library cells
+[INFO ODB-0128] Design: gcd
+[INFO ODB-0130]     Created 54 pins.
+[INFO ODB-0131]     Created 676 components and 2850 component-terminals.
+[INFO ODB-0133]     Created 579 nets and 1498 connections.
+[WARNING GRT-0008] The read_guides command does not allow parasitics estimation from the guides file.
+Summary 1 / 1 (100% pass)
+pass

src/grt/test/incremental_restore_vias.tcl

@@ -0,0 +1,46 @@
+# Routes restored from DB guides during an incremental ECO must be
+# electrically connected by construction (GlobalRouter::addImplicitVias).
+#
+# When guides do not carry explicit via info, boxToGlobalRouting leaves layer
+# transitions implicit, so the per-net parasitic network splits into
+# disconnected islands. The driver-reduced wire capacitance then collapses to
+# zero (the orphaned cap is unreachable from the driver), even though the SPEF
+# still dumps every node. addImplicitVias bridges the coincident adjacent-layer
+# points so the restored route is a single connected network.
+#
+# This test forces the incremental single-net guide-restore path
+# (loadRoutingFromDBGuides) via the ODB journal: deleting a net's guides inside
+# an ECO and undoing it recreates the guides and fires the
+# inDbNetPostGuideRestore callback, marking the net for route restoration.
+source "helpers.tcl"
+read_lef Nangate45/Nangate45.lef
+read_liberty Nangate45/Nangate45_typ.lib
+read_def gcd.def
+read_guides est_rc3.guide
+set_routing_layers -signal metal2-metal10
+
+set block [ord::get_db_block]
+set clk_net [$block findNet "clk"]
+
+# Trigger the journal-driven guide restore for clk.
+global_route -start_incremental
+odb::dbDatabase_beginEco $block
+foreach guide [$clk_net getGuides] {
+  odb::dbGuide_destroy $guide
+}
+odb::dbDatabase_undoEco $block
+global_route -end_incremental
+
+# Estimate parasitics from the restored route and read the driver-reduced wire
+# capacitance (this is what collapses to 0 when the network is fragmented).
+estimate_parasitics -global_routing
+with_output_to_variable report { report_net -digits 5 clk }
+regexp {Wire capacitance:\s+([0-9.]+)} $report -> wire_cap
+
+# Without addImplicitVias the restored clk network is fragmented and this is
+# 0.0; with the fix the driver reaches the whole net (~17.3).
+check "restored clk route is connected (non-zero wire capacitance)" {
+  expr {$wire_cap > 1.0}
+} 1
+
+exit_summary