wip(assembler): round S14 -- 4-way column cache + memoized MC gradients (output unchanged)

Worker-local XY column cache uses deterministic 4-way sets at LOD3-8: LOD4
misses 8,224 -> 1,437, conflicts 7,407 -> 0 (direct-map control: 6.62 s /
43.5 worker-s vs 4.24 s / 21.7). Exact LOD0 lattice gradients memoized per
tile: MC-exclusive 242 -> 201 ns/sample, two-pass loop unchanged. Hashes
identical, no recipe bump. Primary cold trace 4.24 s full set, ring 0.45 s,
75/75 at 40 m/s; a repeat ran uniformly ~40% slower on every LOD (machine
contention suspected); tick p95 to re-check on an idle machine. CVars
voxel.CoreColumnCacheDirectMapped / voxel.CoreMCGradientMemoization.
Report: Standalone/Research/WorldAssemblerM3/Round18.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Standalone/Core/src/VoxelForgeCore.cpp

@@ -1325,6 +1325,11 @@ namespace VoxelForgeCore
     std::optional<TileMesh> World::generateTile(const TileKey& key,const TileGenerationOptions& options,
                                                 std::string& error) const
     {
+        // Fine owner tiles had zero direct-map conflict evictions in the cold audit. Keep their
+        // single-probe path and use associativity for the coarse coordinate families that collide.
+        // Les tuiles proches n'avaient aucun conflit; garder leur acces simple et associer les LOD grossiers.
+        Heightfield2D::setThreadColumnCacheLegacyDirectMapped(
+            options.legacyDirectMappedColumnCache||key.lod<=2);
         if(!impl_||!impl_->owner||!impl_->shape||!impl_->shape->IsBuilt())
         { error="world must be compiled before generating tiles";return std::nullopt; }
         const auto& world=*impl_->owner;
@@ -1342,6 +1347,7 @@ namespace VoxelForgeCore
         mesher.bStandaloneSkipUvAndColors=options.skipUvAndColors;
         mesher.bStandaloneSkipUV=options.skipUv;mesher.bStandaloneSkipColors=options.skipColors;
         mesher.bStandaloneSkipMaterialGroups=options.skipMaterialGroups;
+        mesher.bStandaloneEnableGradientMemoization=options.memoizeMcGradients;
         mesher.bGenerateSkirts=world.bGenerateSkirts;
         mesher.SkirtCells=static_cast<float>(world.SkirtCells)
             *static_cast<float>(world.OwnerVoxelSizeMicrons)
@@ -1436,6 +1442,7 @@ namespace VoxelForgeCore
             }
         }
         int64 sampleCount=0;std::vector<float> densityValues;
+        FVoxelMarchingCubesStageTimings McStageTimings;
         TileMesh out;out.key=key;
         out.diagnostics.featureRefinedResolution=bFeatureRefinedResolution;
         const bool bHasWorldAssembly=impl_->worldAssembly!=nullptr;
@@ -1523,6 +1530,7 @@ namespace VoxelForgeCore
                     out.diagnostics.unclampedFieldCalls=Counts.NativeUnclampedFieldCalls;
                     out.diagnostics.columnCacheHits=Columns.columnHits;
                     out.diagnostics.columnCacheMisses=Columns.columnMisses;
+                    out.diagnostics.columnCacheConflictMisses=Columns.columnConflictMisses;
                     out.diagnostics.classificationMilliseconds=Counts.Milliseconds;
                     out.diagnostics.classificationExclusiveMilliseconds=std::max(0.0,
                         Counts.Milliseconds-classificationColumnComputeMilliseconds);
@@ -1670,7 +1678,8 @@ namespace VoxelForgeCore
         const auto MarchingCubesStart=std::chrono::steady_clock::now();
         FVoxelMeshData mesh=mesher.GenerateMesh(origin,step,cells,nullptr,
             MeshBandMinZVoxel,MeshBandMaxZVoxel,&sampleCount,nullptr,nullptr,
-            (options.hashDensity||options.captureDensitySamples)?&densityValues:nullptr);
+            (options.hashDensity||options.captureDensitySamples)?&densityValues:nullptr,
+            options.profileMesherStages?&McStageTimings:nullptr);
         const double MarchingCubesWallMilliseconds=std::chrono::duration<double,std::milli>(
             std::chrono::steady_clock::now()-MarchingCubesStart).count();
         const double ColumnMillisecondsAfterMeshing=
@@ -1679,6 +1688,24 @@ namespace VoxelForgeCore
             MarchingCubesWallMilliseconds-(ColumnMillisecondsAfterMeshing-ColumnMillisecondsBeforeMeshing));
         out.diagnostics.marchingCubesColumnComputeMilliseconds=std::max(0.0,
             ColumnMillisecondsAfterMeshing-ColumnMillisecondsBeforeMeshing);
+        if(options.profileMesherStages)
+        {
+            out.diagnostics.marchingCubesDensityGridMilliseconds=McStageTimings.DensityGridMilliseconds;
+            out.diagnostics.marchingCubesCellClassificationMilliseconds=
+                McStageTimings.CellClassificationMilliseconds;
+            out.diagnostics.marchingCubesGradientNormalsMilliseconds=
+                McStageTimings.GradientNormalsMilliseconds;
+            out.diagnostics.marchingCubesEdgeInterpolationMilliseconds=
+                McStageTimings.EdgeInterpolationMilliseconds;
+            out.diagnostics.marchingCubesVertexDedupStreamMilliseconds=
+                McStageTimings.VertexDedupStreamMilliseconds;
+            out.diagnostics.marchingCubesOtherMilliseconds=McStageTimings.OtherMilliseconds;
+            out.diagnostics.marchingCubesGradientFallbackDensityCalls=
+                McStageTimings.GradientFallbackDensityCalls;
+            out.diagnostics.marchingCubesEdgeMidpointDensityCalls=
+                McStageTimings.EdgeMidpointDensityCalls;
+            out.diagnostics.marchingCubesGradientMemoHits=McStageTimings.GradientMemoHits;
+        }
         const double MeshingMilliseconds=std::chrono::duration<double,std::milli>(
             std::chrono::steady_clock::now()-MeshingStart).count();
         out.diagnostics.farHorizonVersion=key.lod>=4?options.farHorizonVersion:0;
@@ -1765,6 +1792,7 @@ namespace VoxelForgeCore
             out.diagnostics.unclampedFieldCalls=Counts.NativeUnclampedFieldCalls;
             out.diagnostics.columnCacheHits=Columns.columnHits;
             out.diagnostics.columnCacheMisses=Columns.columnMisses;
+            out.diagnostics.columnCacheConflictMisses=Columns.columnConflictMisses;
             out.diagnostics.columnComputeMilliseconds=Columns.columnComputeMilliseconds;
             out.diagnostics.columnEvaluationExclusiveMilliseconds=Columns.columnComputeMilliseconds;
             out.diagnostics.classificationMilliseconds=Counts.Milliseconds;

Standalone/Core/src/WorldAssemblerInternal.h

@@ -1361,11 +1361,35 @@ namespace world_assembly_detail
         std::int64_t x = 0, y = 0;
         HeightfieldPointSample column{};
     };
-    // Coarse LOD tiles revisit a wider set of gradient-sample columns than the full-resolution
-    // band. Keep those columns resident for a complete worker tile so the 3D mesher does not
-    // repeat the procedural biome evaluation for every Z sample.
+    // Keep 65,536 entries in each worker cache; four ways tolerate coordinate families that
+    // deliberately share low hash bits at coarse LODs.
+    // Chaque cache worker garde 65 536 entrees; quatre voies absorbent les coordonnees grossieres
+    // qui partagent les bits faibles du hash.
+    constexpr std::size_t HeightfieldColumnCacheWays=4;
+    constexpr std::size_t HeightfieldColumnCacheSetCount=65536/HeightfieldColumnCacheWays;
     inline thread_local std::array<HeightfieldColumnCacheEntry, 65536> HeightfieldColumnCache{};
+    inline thread_local std::array<std::uint8_t, HeightfieldColumnCacheSetCount>
+        HeightfieldColumnCacheNextWay{};
     inline thread_local HeightfieldColumnCacheStats HeightfieldColumnStats{};
+    inline thread_local bool HeightfieldColumnCacheLegacyDirectMapped=false;
+
+    inline std::size_t HeightfieldColumnCacheSet(const WorldAssemblyRecipeV1& recipe,
+        const WorldAssemblyStratumPlanV1& plan,std::int64_t x,std::int64_t y) noexcept
+    {
+        // Avalanche every coordinate bit before masking. The old direct hash kept too little
+        // entropy from widely spaced coarse LOD coordinates in its low 16 bits.
+        // Melanger tous les bits de coordonnee avant le masque; l'ancien hash perdait de
+        // l'entropie sur les coordonnees espacees des LOD grossiers.
+        std::uint64_t mixed=static_cast<std::uint64_t>(x)*0x9E3779B185EBCA87ull
+            ^std::rotl(static_cast<std::uint64_t>(y)*0xC2B2AE3D27D4EB4Full,29)
+            ^recipe.contentHash^std::rotl(plan.contentHash,17);
+        mixed^=mixed>>30;
+        mixed*=0xBF58476D1CE4E5B9ull;
+        mixed^=mixed>>27;
+        mixed*=0x94D049BB133111EBull;
+        mixed^=mixed>>31;
+        return static_cast<std::size_t>(mixed)&(HeightfieldColumnCacheSetCount-1);
+    }
 
     inline HeightfieldPointSample EvaluateColumn(const WorldAssemblyRecipeV1& recipe,
         const WorldAssemblyStratumPlanV1& plan,std::int64_t x,std::int64_t y)
@@ -1480,15 +1504,48 @@ namespace world_assembly_detail
     inline HeightfieldPointSample CachedColumn(const WorldAssemblyRecipeV1& recipe,
         const WorldAssemblyStratumPlanV1& plan,std::int64_t x,std::int64_t y)
     {
-        const std::uint64_t mixed=(static_cast<std::uint64_t>(x)*0x9E3779B185EBCA87ull)
-            ^std::rotl(static_cast<std::uint64_t>(y)*0xC2B2AE3D27D4EB4Full,23)
-            ^static_cast<std::uint64_t>(reinterpret_cast<std::uintptr_t>(&recipe))
-            ^std::rotl(static_cast<std::uint64_t>(reinterpret_cast<std::uintptr_t>(&plan)),41);
-        auto& entry=HeightfieldColumnCache[static_cast<std::size_t>(mixed)&
-            (HeightfieldColumnCache.size()-1)];
-        if(entry.recipe==&recipe&&entry.plan==&plan&&entry.recipeHash==recipe.contentHash
-            &&entry.planHash==plan.contentHash&&entry.x==x&&entry.y==y)
-        {++HeightfieldColumnStats.columnHits;return entry.column;}
+        HeightfieldColumnCacheEntry* replacement=nullptr;
+        if(HeightfieldColumnCacheLegacyDirectMapped)
+        {
+            // Preserve S13's exact direct-map index as an in-process negative control.
+            // Conserver l'index direct exact de S13 comme controle negatif en cours d'execution.
+            const std::uint64_t mixed=(static_cast<std::uint64_t>(x)*0x9E3779B185EBCA87ull)
+                ^std::rotl(static_cast<std::uint64_t>(y)*0xC2B2AE3D27D4EB4Full,23)
+                ^static_cast<std::uint64_t>(reinterpret_cast<std::uintptr_t>(&recipe))
+                ^std::rotl(static_cast<std::uint64_t>(reinterpret_cast<std::uintptr_t>(&plan)),41);
+            replacement=&HeightfieldColumnCache[static_cast<std::size_t>(mixed)
+                &(HeightfieldColumnCache.size()-1)];
+            if(replacement->recipe==&recipe&&replacement->plan==&plan
+                &&replacement->recipeHash==recipe.contentHash
+                &&replacement->planHash==plan.contentHash&&replacement->x==x&&replacement->y==y)
+            {++HeightfieldColumnStats.columnHits;return replacement->column;}
+            if(replacement->recipe!=nullptr)++HeightfieldColumnStats.columnConflictMisses;
+        }
+        else
+        {
+            const std::size_t set=HeightfieldColumnCacheSet(recipe,plan,x,y);
+            const std::size_t first=set*HeightfieldColumnCacheWays;
+            std::size_t replacementWay=HeightfieldColumnCacheWays;
+            for(std::size_t way=0;way<HeightfieldColumnCacheWays;++way)
+            {
+                auto& candidate=HeightfieldColumnCache[first+way];
+                if(candidate.recipe==&recipe&&candidate.plan==&plan
+                    &&candidate.recipeHash==recipe.contentHash&&candidate.planHash==plan.contentHash
+                    &&candidate.x==x&&candidate.y==y)
+                {++HeightfieldColumnStats.columnHits;return candidate.column;}
+                if(candidate.recipe==nullptr&&replacementWay==HeightfieldColumnCacheWays)
+                    replacementWay=way;
+            }
+            if(replacementWay==HeightfieldColumnCacheWays)
+            {
+                ++HeightfieldColumnStats.columnConflictMisses;
+                replacementWay=HeightfieldColumnCacheNextWay[set];
+            }
+            HeightfieldColumnCacheNextWay[set]=static_cast<std::uint8_t>(
+                (replacementWay+1)%HeightfieldColumnCacheWays);
+            replacement=&HeightfieldColumnCache[first+replacementWay];
+        }
+        auto& entry=*replacement;
         const auto start=std::chrono::steady_clock::now();
         HeightfieldPointSample column=EvaluateColumn(recipe,plan,x,y);
         HeightfieldColumnStats.columnComputeMilliseconds+=std::chrono::duration<double,std::milli>(
@@ -1977,19 +2034,27 @@ void Heightfield2D::resetThreadColumnCacheStats(bool captureCoordinates, bool cl
 {
     // Diagnostic probes may clear old tile entries before comparing isolated sample grids.
     // Les sondes de mesure peuvent vider les entrees d'une tuile avant de comparer deux grilles.
-    if(clearCache)world_assembly_detail::HeightfieldColumnCache.fill(
-        world_assembly_detail::HeightfieldColumnCacheEntry{});
+    if(clearCache)
+    {
+        world_assembly_detail::HeightfieldColumnCache.fill(
+            world_assembly_detail::HeightfieldColumnCacheEntry{});
+        world_assembly_detail::HeightfieldColumnCacheNextWay.fill(0);
+    }
     auto& Stats=world_assembly_detail::HeightfieldColumnStats;
     world_assembly_detail::HeightfieldColumnOctaveDrop=octaveDrop;
     Stats.pointCalls=0;
     Stats.columnHits=0;
     Stats.columnMisses=0;
+    Stats.columnConflictMisses=0;
     Stats.columnComputeMilliseconds=0.0;
     Stats.captureCoordinates=captureCoordinates;
     Stats.coordinateCaptureComplete=true;
     Stats.evaluatedCoordinates.clear();
 }
 
+void Heightfield2D::setThreadColumnCacheLegacyDirectMapped(bool enabled) noexcept
+{ world_assembly_detail::HeightfieldColumnCacheLegacyDirectMapped=enabled; }
+
 const HeightfieldColumnCacheStats& Heightfield2D::threadColumnCacheStats() noexcept
 { return world_assembly_detail::HeightfieldColumnStats; }