From 044c9ba2d4e66cf34214fdfd62fb90a872da64b1 Mon Sep 17 00:00:00 2001
From: Maciej Kurc <mkurc@antmicro.com>
Date: Fri, 16 Jul 2021 13:28:40 +0200
Subject: LUT mapping cache optimizations 1

Signed-off-by: Maciej Kurc <mkurc@antmicro.com>
---
 fpga_interchange/site_lut_mapping_cache.cc | 28 ++++++++++++----
 fpga_interchange/site_lut_mapping_cache.h  | 52 +++++++++++++++---------------
 2 files changed, 48 insertions(+), 32 deletions(-)

diff --git a/fpga_interchange/site_lut_mapping_cache.cc b/fpga_interchange/site_lut_mapping_cache.cc
index bcde7621..03ef03be 100644
--- a/fpga_interchange/site_lut_mapping_cache.cc
+++ b/fpga_interchange/site_lut_mapping_cache.cc
@@ -73,29 +73,44 @@ SiteLutMappingKey SiteLutMappingKey::create (const SiteInformation& siteInfo) {
         cell.type       = cellInfo->type;
         cell.belIndex   = cellInfo->bel.index;
 
+        memset((void*)cell.conns, 0,
+               sizeof(int32_t) * SiteLutMappingKey::MAX_LUT_INPUTS);
+
+        size_t portId = 0;
         for (const auto& port : cellInfo->ports) {
             const auto& portInfo = port.second;
+
+            // Consider only LUT inputs
+            if (portInfo.type != PORT_IN) {
+                continue;
+            }
+
+            // Assign net id if any
+            int32_t netId = 0;
             if (portInfo.net != nullptr) {
                 auto    netInfo = portInfo.net;
-                int32_t netId   = -1;
 
                 auto it = netMap.find(netInfo->name);
                 if (it != netMap.end()) {
                     netId = it->second;
                 }
                 else {
-                    netId = (int32_t)netMap.size();
+                    netId = (int32_t)netMap.size() + 1;
                     netMap[netInfo->name] = netId;
                 }
-
-                cell.conns[portInfo.name] = netId;
             }
+
+            NPNR_ASSERT(portId < SiteLutMappingKey::MAX_LUT_INPUTS);
+            cell.conns[portId++] = netId;
         }
 
         // Add the cell entry
         key.cells.push_back(cell);
     }
 
+    // Compute hash
+    key.computeHash();
+
     return key;
 }
 
@@ -120,9 +135,10 @@ bool SiteLutMappingResult::apply (const SiteInformation& siteInfo) {
         // Cell <-> BEL pin map
         size_t numPins = cellInfo->lut_cell.pins.size();
         for (size_t pinIdx = 0; pinIdx < numPins; ++pinIdx) {
-            IdString cellPin = cellInfo->lut_cell.pins[pinIdx];
-            auto &belPins    = cellInfo->cell_bel_pins[cellPin];
+            const IdString& cellPin = cellInfo->lut_cell.pins[pinIdx];
+            auto &belPins           = cellInfo->cell_bel_pins[cellPin];
 
+            // There is only one pin
             belPins.resize(1);
             belPins[0] = cell.belPins[cellPin];
         }
diff --git a/fpga_interchange/site_lut_mapping_cache.h b/fpga_interchange/site_lut_mapping_cache.h
index 4a81711f..b07e3e77 100644
--- a/fpga_interchange/site_lut_mapping_cache.h
+++ b/fpga_interchange/site_lut_mapping_cache.h
@@ -28,6 +28,11 @@ NEXTPNR_NAMESPACE_BEGIN
 // Key structure used in site LUT mapping cache
 struct SiteLutMappingKey {
 
+    // Maximum number of LUT cells
+    static constexpr size_t MAX_LUT_CELLS  = 8;
+    // Maximum number of LUT inputs per cell
+    static constexpr size_t MAX_LUT_INPUTS = 6;
+
     // LUT Cell data
     struct Cell {
         IdString    type;       // Cell type
@@ -35,51 +40,46 @@ struct SiteLutMappingKey {
   
         // Port to net assignments. These are local net ids generated during
         // key creation. This is to abstract connections from actual design
-        // net names.
-        dict<IdString, int32_t> conns;
-
-        bool operator == (const Cell& other) const {
-            return  (type == other.type) &&
-                    (belIndex == other.belIndex) &&
-                    (conns == other.conns);
-        }
-
-        bool operator < (const Cell& other) const {            
-            return belIndex < other.belIndex;
-        }
+        // net names. the Id 0 means unconnected.
+        int32_t     conns [MAX_LUT_INPUTS];
     };
 
     int32_t           tileType; // Tile type
     int32_t           siteType; // Site type in that tile type
     std::vector<Cell> cells;    // LUT cell data
 
+    unsigned int      hash_;    // Precomputed hash
+
     static SiteLutMappingKey create (const SiteInformation& siteInfo);
+
+    void computeHash () {
+        hash_ = mkhash(0, tileType);
+        hash_ = mkhash(hash_, siteType);
+        for (const auto& cell : cells) {
+            hash_ = mkhash(hash_, cell.type.index);
+            hash_ = mkhash(hash_, cell.belIndex);
+            for (size_t i=0; i<MAX_LUT_INPUTS; ++i) {
+                hash_ = mkhash(hash_, cell.conns[i]);
+            }
+        }
+    }
    
     bool operator == (const SiteLutMappingKey &other) const {
-        return (tileType == other.tileType) &&
+        return (hash_ == other.hash_) &&
+               (tileType == other.tileType) &&
                (siteType == other.siteType) &&
                (cells == other.cells);
     }
 
     bool operator != (const SiteLutMappingKey &other) const {
-        return (tileType != other.tileType) ||
+        return (hash_ != other.hash_) ||
+               (tileType != other.tileType) ||
                (siteType != other.siteType) ||
                (cells != other.cells);
     }
 
     unsigned int hash () const {
-        unsigned int h = 0;
-        h = mkhash(h, tileType);
-        h = mkhash(h, siteType);
-        for (const auto& cell : cells) {
-            h = mkhash(h, cell.type.index);
-            h = mkhash(h, cell.belIndex);
-            for (const auto& conn : cell.conns) {
-                h = mkhash(h, conn.first.index);
-                h = mkhash(h, conn.second);
-            }
-        }
-        return h;
+        return hash_;
     }
 };
 
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