perf: scale Expr.replace cache with input size

src/Lean/Util/ReplaceExpr.lean

@@ -1,7 +1,7 @@
 /-
 Copyright (c) 2020 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Leonardo de Moura
+Authors: Leonardo de Moura, Gabriel Ebner, Sebastian Ullrich
 -/
 import Lean.Expr
 
@@ -10,40 +10,40 @@ namespace Expr
 
 namespace ReplaceImpl
 
-@[inline] def cacheSize : USize := 8192 - 1
-
 structure Cache where
-  -- First cacheSize elements are the keys.
-  -- Second cacheSize elements are the results.
+  size : USize
+  -- First `size` elements are the keys.
+  -- Second `size` elements are the results.
   keysResults : Array NonScalar -- Either Expr or Unit (disjoint memory representation)
 
-set_option compiler.extract_closed false in
-unsafe def Cache.new : Cache :=
-  { keysResults := mkArray (2 * cacheSize).toNat (unsafeCast ()) }
+unsafe def Cache.new (e : Expr) : Cache :=
+  -- scale size with approximate number of subterms up to 8k
+  -- make sure size is coprime with power of two for collision avoidance
+  let size := (1 <<< min (max e.approxDepth.toUSize 1) 13) - 1
+  { size, keysResults := mkArray (2 * size).toNat (unsafeCast ()) }
 
 @[inline]
-unsafe def Cache.keyIdx (key : Expr) : USize :=
-  ptrAddrUnsafe key % cacheSize
+unsafe def Cache.keyIdx (c : Cache) (key : Expr) : USize :=
+  ptrAddrUnsafe key % c.size
 
 @[inline]
-unsafe def Cache.resultIdx (key : Expr) : USize :=
-  keyIdx key + cacheSize
+unsafe def Cache.resultIdx (c : Cache) (key : Expr) : USize :=
+  c.keyIdx key + c.size
 
 @[inline]
 unsafe def Cache.hasResultFor (c : Cache) (key : Expr) : Bool :=
-  have : (keyIdx key).toNat < c.keysResults.size := lcProof
-  ptrEq (unsafeCast key) c.keysResults[keyIdx key]
+  have : (c.keyIdx key).toNat < c.keysResults.size := lcProof
+  ptrEq (unsafeCast key) c.keysResults[c.keyIdx key]
 
 @[inline]
 unsafe def Cache.getResultFor (c : Cache) (key : Expr) : Expr :=
-  have : (resultIdx key).toNat < c.keysResults.size := lcProof
-  unsafeCast c.keysResults[resultIdx key]
+  have : (c.resultIdx key).toNat < c.keysResults.size := lcProof
+  unsafeCast c.keysResults[c.resultIdx key]
 
-@[inline]
 unsafe def Cache.store (c : Cache) (key result : Expr) : Cache :=
-  Cache.mk <| c.keysResults
-    |>.uset (keyIdx key) (unsafeCast key) lcProof
-    |>.uset (resultIdx key) (unsafeCast result) lcProof
+  { c with keysResults := c.keysResults
+    |>.uset (c.keyIdx key) (unsafeCast key) lcProof
+    |>.uset (c.resultIdx key) (unsafeCast result) lcProof }
 
 abbrev ReplaceM := StateM Cache
 
@@ -71,7 +71,7 @@ unsafe def replaceUnsafeM (f? : Expr → Option Expr) (e : Expr) : ReplaceM Expr
 
 @[inline]
 unsafe def replaceUnsafe (f? : Expr → Option Expr) (e : Expr) : Expr :=
-  (replaceUnsafeM f? e).run' Cache.new
+  (replaceUnsafeM f? e).run' (Cache.new e)
 
 end ReplaceImpl