interchange: Fix illegal placements

Signed-off-by: gatecat <gatecat@ds0.me>

2 files changed, 8 insertions, 7 deletions

diff --git a/common/placer1.cc b/common/placer1.cc
index c2698ad9..1f940dac 100644
--- a/common/placer1.cc
+++ b/common/placer1.cc
@@ -552,7 +552,9 @@ class SAPlacer
             add_move_cell(moveChange, other_cell, newBel);
         }
 
-        if (!ctx->isBelLocationValid(newBel) || ((other_cell != nullptr && !ctx->isBelLocationValid(oldBel)))) {
+        // Always check both the new and old locations; as in some cases of dedicated routing ripping up a cell can deny
+        // use of a dedicated path and thus make a site illegal
+        if (!ctx->isBelLocationValid(newBel) || !ctx->isBelLocationValid(oldBel)) {
             ctx->unbindBel(newBel);
             if (other_cell != nullptr)
                 ctx->unbindBel(oldBel);
diff --git a/fpga_interchange/arch.h b/fpga_interchange/arch.h
index 642060cc..cb137ef6 100644
--- a/fpga_interchange/arch.h
+++ b/fpga_interchange/arch.h
@@ -808,9 +808,7 @@ struct Arch : ArchAPI<ArchRanges>
         }
         const TileStatus &tile_status = iter->second;
         const CellInfo *cell = tile_status.boundcells[bel.index];
-        if (cell == nullptr) {
-            return true;
-        } else {
+        if (cell != nullptr) {
             if (!dedicated_interconnect.isBelLocationValid(bel, cell)) {
                 return false;
             }
@@ -825,10 +823,11 @@ struct Arch : ArchAPI<ArchRanges>
             if (!is_cell_valid_constraints(cell, tile_status, explain_constraints)) {
                 return false;
             }
-
-            auto &bel_data = bel_info(chip_info, bel);
-            return get_site_status(tile_status, bel_data).checkSiteRouting(getCtx(), tile_status);
         }
+        // Still check site status if cell is nullptr; as other bels in the site could be illegal (for example when
+        // dedicated paths can no longer be used after ripping up a cell)
+        auto &bel_data = bel_info(chip_info, bel);
+        return get_site_status(tile_status, bel_data).checkSiteRouting(getCtx(), tile_status);
     }
 
     IdString get_bel_tiletype(BelId bel) const { return IdString(loc_info(chip_info, bel).name); }