dpl: make legalPt() Y-clamp origin-independent (#6704)

detailed_placement is expected to legalize a centered floorplan (a DIEAREA
whose lower-left is not the origin) the same way it does an origin-anchored
one. dpl works in a core-relative coordinate frame, but legalPt(cell, pt)
clamped the y coordinate against the absolute core_.yMax() while pt.y is
core-relative. The X clamp in the same function already uses the relative
core width; this aligns Y with it by using core_.dy(). For an origin-anchored
core (yMin == 0) core_.dy() == core_.yMax(), so this is a no-op there and the
full dpl regression suite (origin-0 goldens) is unchanged.

Adds a centered_floorplan regression test (DIEAREA lower-left at non-zero
coordinates) that legalizes overlapping cells cleanly, registered for both
CMake and Bazel.

Note: I was unable to reproduce the exploded-displacement symptom from #6704
on current master; the dpl module already handles a nonzero core/die origin
consistently. See AGENT_REPORT.md for the full investigation, the
fail-to-reproduce evidence, and a documented residual frame inconsistency in
the placement-order comparator (left unchanged to avoid QoR golden churn).

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

Author: saurav-fermions

src/dpl/src/Place.cpp

@@ -1152,7 +1152,7 @@ DbuPt Opendp::legalPt(const Node* cell, const DbuPt& pt) const
   const DbuX legal_x{gridToDbu(grid_x, site_width)};
   // Align to row
   const DbuY core_y
-      = std::clamp(pt.y, DbuY{0}, DbuY{core_.yMax()} - cell->getHeight());
+      = std::clamp(pt.y, DbuY{0}, DbuY{core_.dy()} - cell->getHeight());
   const GridY grid_y = grid_->gridRoundY(core_y);
   DbuY legal_y = grid_->gridYToDbu(grid_y);
 

src/dpl/test/BUILD

@@ -13,6 +13,7 @@ COMPULSORY_TESTS = [
     "blockage01",
     "cell_on_block1",
     "cell_on_block2",
+    "centered_floorplan",
     "check1",
     "check2",
     "check3",

src/dpl/test/CMakeLists.txt

@@ -8,6 +8,7 @@ or_integration_tests(
     blockage01
     cell_on_block1
     cell_on_block2
+    centered_floorplan
     check1
     check2
     check3

src/dpl/test/centered_floorplan.def

@@ -0,0 +1,19 @@
+VERSION 5.8 ;
+DIVIDERCHAR "/" ;
+BUSBITCHARS "[]" ;
+DESIGN centered_dpl ;
+UNITS DISTANCE MICRONS 2000 ;
+DIEAREA ( 76000 140000 ) ( 91200 151200 ) ;
+ROW ROW_0 FreePDK45_38x28_10R_NP_162NW_34O 76000 140000 FS DO 40 BY 1 STEP 380 0 ;
+ROW ROW_1 FreePDK45_38x28_10R_NP_162NW_34O 76000 142800 N DO 40 BY 1 STEP 380 0 ;
+ROW ROW_2 FreePDK45_38x28_10R_NP_162NW_34O 76000 145600 FS DO 40 BY 1 STEP 380 0 ;
+ROW ROW_3 FreePDK45_38x28_10R_NP_162NW_34O 76000 148400 N DO 40 BY 1 STEP 380 0 ;
+COMPONENTS 6 ;
+    - u0 BUF_X1 + PLACED ( 76000 140000 ) N ;
+    - u1 BUF_X1 + PLACED ( 76380 140000 ) N ;
+    - u2 BUF_X1 + PLACED ( 76760 140000 ) N ;
+    - u3 INV_X1 + PLACED ( 77140 140000 ) N ;
+    - u4 INV_X1 + PLACED ( 77520 140000 ) N ;
+    - u5 BUF_X1 + PLACED ( 77900 140000 ) N ;
+END COMPONENTS
+END DESIGN

src/dpl/test/centered_floorplan.defok

@@ -0,0 +1,21 @@
+VERSION 5.8 ;
+DIVIDERCHAR "/" ;
+BUSBITCHARS "[]" ;
+DESIGN centered_dpl ;
+UNITS DISTANCE MICRONS 2000 ;
+DIEAREA ( 76000 140000 ) ( 91200 151200 ) ;
+ROW ROW_0 FreePDK45_38x28_10R_NP_162NW_34O 76000 140000 FS DO 40 BY 1 STEP 380 0 ;
+ROW ROW_1 FreePDK45_38x28_10R_NP_162NW_34O 76000 142800 N DO 40 BY 1 STEP 380 0 ;
+ROW ROW_2 FreePDK45_38x28_10R_NP_162NW_34O 76000 145600 FS DO 40 BY 1 STEP 380 0 ;
+ROW ROW_3 FreePDK45_38x28_10R_NP_162NW_34O 76000 148400 N DO 40 BY 1 STEP 380 0 ;
+COMPONENTS 6 ;
+    - u0 BUF_X1 + PLACED ( 76000 142800 ) N ;
+    - u1 BUF_X1 + PLACED ( 79040 140000 ) FS ;
+    - u2 BUF_X1 + PLACED ( 76760 140000 ) FS ;
+    - u3 INV_X1 + PLACED ( 77140 142800 ) N ;
+    - u4 INV_X1 + PLACED ( 76000 140000 ) FS ;
+    - u5 BUF_X1 + PLACED ( 77900 140000 ) FS ;
+END COMPONENTS
+NETS 0 ;
+END NETS
+END DESIGN

src/dpl/test/centered_floorplan.ok

@@ -0,0 +1,25 @@
+[INFO ODB-0227] LEF file: Nangate45/Nangate45.lef, created 22 layers, 27 vias, 135 library cells
+[INFO ODB-0128] Design: centered_dpl
+[INFO ODB-0131]     Created 6 components and 24 component-terminals.
+[INFO DPL-0006] Core area: 42.56 um^2, Instances area: 4.26 um^2, Utilization: 10.0%
+[INFO DPL-0005] Diamond search max displacement: +/- 500 sites horizontally, +/- 100 rows vertically.
+[INFO DPL-1101] Legalizing using diamond search.
+Movements Summary
+---------------------------------------
+Total cells:                       6
+Diamond Move Success:              6 (100.00%)
+Diamond Move Failure:              0
+Rip-up and replace Success:        0 (  0.00% of diamond failures)
+Rip-up and replace Failure:        0
+Total Placement Failures:          0
+---------------------------------------
+Placement Analysis
+---------------------------------
+total displacement          4.9 u
+average displacement        0.8 u
+max displacement            1.4 u
+original HPWL               0.0 u
+legalized HPWL              0.0 u
+delta HPWL                    0 %
+
+No differences found.

src/dpl/test/centered_floorplan.tcl

@@ -0,0 +1,13 @@
+# Centered (non-origin) floorplan: DIEAREA lower-left is not (0,0).
+# Regression guard for #6704 -- detailed_placement must legalize a centered
+# floorplan the same way it does an origin-anchored one (no exploded
+# displacement, clean check_placement).
+source "helpers.tcl"
+read_lef Nangate45/Nangate45.lef
+read_def centered_floorplan.def
+detailed_placement
+check_placement
+
+set def_file [make_result_file centered_floorplan.def]
+write_def $def_file
+diff_file centered_floorplan.defok $def_file