pdn: prevent pad connections from targeting macro grid shapes (#10490)

Pad direct connections (PadDirectConnectionStraps) snap to the closest
valid STRIPE/RING target on a connectable layer. isTargetShape() accepted
any such shape regardless of its owning grid. When a macro (instance) PDN
grid is built before the core grid, its in-core stripes become visible
target candidates; with no core target on the pad-connect layer near the
pad, the pad connection snapped to a macro stripe and extended deep into
the core.

Reject shapes owned by an instance grid (Grid::kInstance) as pad-connect
targets so pad connections only land on core/existing grid shapes.

Add regression test pads_black_parrot_macro_grid (CMake + Bazel) that
reproduces the symptom: baseline reports 99 pad connections extending into
the core (worst reach ~1.4mm); with the fix, 0.

Signed-off-by: Saurav Singh <saurav.singh@fermions.co>

Author: saurav-fermions

src/pdn/src/straps.cpp

@@ -1590,6 +1590,19 @@ bool PadDirectConnectionStraps::refineShape(
 
 bool PadDirectConnectionStraps::isTargetShape(const Shape* shape) const
 {
+  // Pad direct connections run from a pad pin toward the core power grid.  They
+  // must not target shapes that belong to an instance (macro) grid: those
+  // stripes sit inside the core over the macro, and snapping a pad connection
+  // to them drags the connection deep into the core (issue #10490).  Only
+  // shapes owned by core/existing grids are valid landing targets.
+  const auto* component = shape->getGridComponent();
+  if (component != nullptr) {
+    const auto* grid = component->getGrid();
+    if (grid != nullptr && grid->type() == Grid::kInstance) {
+      return false;
+    }
+  }
+
   if (target_shapes_type_) {
     return shape->getType() == target_shapes_type_.value();
   }

src/pdn/test/BUILD

@@ -115,6 +115,7 @@ COMPULSORY_TESTS = [
     "pads_black_parrot_flipchip_connect_overpads",
     "pads_black_parrot_grid_define",
     "pads_black_parrot_limit_connect",
+    "pads_black_parrot_macro_grid",
     "pads_black_parrot_max_width",
     "pads_black_parrot_no_connect",
     "pads_black_parrot_offset",

src/pdn/test/CMakeLists.txt

@@ -111,6 +111,7 @@ or_integration_tests(
     pads_black_parrot_flipchip_connect_overpads
     pads_black_parrot_grid_define
     pads_black_parrot_limit_connect
+    pads_black_parrot_macro_grid
     pads_black_parrot_max_width
     pads_black_parrot_no_connect
     pads_black_parrot_offset

src/pdn/test/pads_black_parrot_macro_grid.ok

@@ -0,0 +1,11 @@
+[INFO ODB-0227] LEF file: Nangate45/Nangate45.lef, created 22 layers, 27 vias, 135 library cells
+[INFO ODB-0227] LEF file: nangate_bsg_black_parrot/dummy_pads.lef, created 24 library cells
+[INFO ODB-0227] LEF file: Nangate45/fakeram45_64x32.lef, created 1 library cells
+[INFO ODB-0128] Design: soc_bsg_black_parrot
+[INFO ODB-0130]     Created 141 pins.
+[INFO ODB-0131]     Created 1514 components and 1480 component-terminals.
+[INFO ODB-0132]     Created 2 special nets and 268 connections.
+[INFO ODB-0133]     Created 350 nets and 390 connections.
+[INFO PDN-0001] Inserting grid: sram - repro_sram
+[INFO PDN-0001] Inserting grid: Core
+pad connections extending into core: 0

src/pdn/test/pads_black_parrot_macro_grid.tcl

@@ -0,0 +1,98 @@
+# Regression for issue #10490: a macro PDN grid must not cause pad direct
+# connections to extend into the core.
+#
+# When pad direct-connect is enabled at the grid level
+# (define_pdn_grid -connect_to_pads), a pad connection snaps to the closest
+# STRIPE/RING target on a connectable layer.  If a macro (instance) PDN grid is
+# built first, its in-core stripes become visible target candidates and -- when
+# there is no core target on the pad-connect layer near the pad -- the pad
+# connection used to snap to those macro stripes, dragging the connection deep
+# into the core.
+#
+# The fix makes PadDirectConnectionStraps::isTargetShape() reject shapes owned
+# by an instance grid, so pad connections only land on core/existing grid
+# shapes.  This test asserts that no pad connection extends past the core
+# boundary.
+source "helpers.tcl"
+
+read_lef Nangate45/Nangate45.lef
+read_lef nangate_bsg_black_parrot/dummy_pads.lef
+read_lef Nangate45/fakeram45_64x32.lef
+
+read_def nangate_bsg_black_parrot/floorplan.def
+
+set block [ord::get_db_block]
+set db [ord::get_db]
+
+# Place an SRAM macro just inside the core, above the south VDD/VSS pads.
+set master [$db findMaster fakeram45_64x32]
+set inst [odb::dbInst_create $block $master "repro_sram"]
+$inst setOrigin 850000 450000
+$inst setPlacementStatus FIRM
+foreach iterm [$inst getITerms] {
+  set name [[$iterm getMTerm] getName]
+  if { [string match "*VDD*" $name] } {
+    odb::dbITerm_connect $iterm [$block findNet VDD]
+  } elseif { [string match "*VSS*" $name] } {
+    odb::dbITerm_connect $iterm [$block findNet VSS]
+  }
+}
+
+add_global_connection -net VDD -pin_pattern {^VDD$} -power
+add_global_connection -net VDD -pin_pattern {^VDDPE$}
+add_global_connection -net VDD -pin_pattern {^VDDCE$}
+add_global_connection -net VSS -pin_pattern {^VSS$} -ground
+add_global_connection -net VSS -pin_pattern {^VSSE$}
+
+set_voltage_domain -power VDD -ground VSS
+
+# Define the macro grid first so it is built before the Core grid; its in-core
+# metal8 stripes are then visible as candidate targets when the Core grid's pad
+# direct-connections are created.
+define_pdn_grid -macro -name "sram" -instances "repro_sram"
+add_pdn_stripe -layer metal8 -width 1.40 -pitch 6.0 -offset 0.5
+add_pdn_stripe -layer metal9 -width 1.40 -pitch 6.0 -offset 0.5
+add_pdn_connect -layers {metal8 metal9}
+
+# Core grid with grid-level pad connect.  The ring is on metal9/metal10 only,
+# so the pad metal8 connection has no metal8 ring near the pads.
+define_pdn_grid -name "Core" -starts_with "POWER" -connect_to_pads
+add_pdn_ring -grid "Core" -layers {metal9 metal10} -widths 5.0 \
+  -spacings 2.0 -core_offsets 2
+
+add_pdn_stripe -layer metal4 -width 0.48 -pitch 56.0 -offset 2.24
+add_pdn_stripe -layer metal7 -width 1.40 -pitch 40.0 -offset 2.70
+add_pdn_stripe -layer metal8 -width 1.40 -pitch 200.0 -offset 100.0
+add_pdn_stripe -layer metal9 -width 1.40 -pitch 40.0 -offset 2.70
+
+add_pdn_connect -layers {metal4 metal7}
+add_pdn_connect -layers {metal7 metal8}
+add_pdn_connect -layers {metal8 metal9}
+add_pdn_connect -layers {metal9 metal10}
+
+pdngen
+
+set core [$block getCoreArea]
+set core_ymin [$core yMin]
+
+# A genuine south pad connection is a narrow vertical metal8 shape rooted in the
+# pad (ymin within the pad y-extent).  Assert that none extends into the core.
+set pad_top 352000
+set bad 0
+foreach net {VDD VSS} {
+  set dnet [$block findNet $net]
+  foreach swire [$dnet getSWires] {
+    foreach wire [$swire getWires] {
+      if { [$wire isVia] } { continue }
+      if { [[$wire getTechLayer] getName] != "metal8" } { continue }
+      set xmin [$wire xMin]; set ymin [$wire yMin]
+      set xmax [$wire xMax]; set ymax [$wire yMax]
+      set dx [expr {$xmax - $xmin}]; set dy [expr {$ymax - $ymin}]
+      if { $dx < 5000 && $dy > $dx && $ymin <= $pad_top && $ymax > $core_ymin } {
+        incr bad
+      }
+    }
+  }
+}
+
+puts "pad connections extending into core: $bad"