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encode black holes as tApp values

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checking for isBlackhole in the forceValue hot path is rather more
expensive than necessary, and with a little bit of trickery we can move
such handling into the isApp case. small performance benefit, but under
some circumstances we've seen 2% improvement as well.

〉 nix eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'

before:

  Time (mean ± σ):      4.429 s ±  0.002 s    [User: 3.929 s, System: 0.500 s]
  Range (min … max):    4.427 s …  4.433 s    10 runs

after:

  Time (mean ± σ):      4.396 s ±  0.002 s    [User: 3.894 s, System: 0.501 s]
  Range (min … max):    4.393 s …  4.399 s    10 runs
This commit is contained in:
pennae 2023-12-10 08:24:45 +01:00
parent 0218e4e6c3
commit 78353deb02
7 changed files with 93 additions and 32 deletions
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24
src/libexpr/value.hh
View file

@ -32,7 +32,6 @@ typedef enum {
tThunk,
tApp,
tLambda,
tBlackhole,
tPrimOp,
tPrimOpApp,
tExternal,
@ -151,7 +150,7 @@ public:
// type() == nThunk
inline bool isThunk() const { return internalType == tThunk; };
inline bool isApp() const { return internalType == tApp; };
inline bool isBlackhole() const { return internalType == tBlackhole; };
inline bool isBlackhole() const;
// type() == nFunction
inline bool isLambda() const { return internalType == tLambda; };
@ -248,7 +247,7 @@ public:
case tLambda: case tPrimOp: case tPrimOpApp: return nFunction;
case tExternal: return nExternal;
case tFloat: return nFloat;
case tThunk: case tApp: case tBlackhole: return nThunk;
case tThunk: case tApp: return nThunk;
}
if (invalidIsThunk)
return nThunk;
@ -356,11 +355,7 @@ public:
lambda.fun = f;
}
inline void mkBlackhole()
{
internalType = tBlackhole;
// Value will be overridden anyways
}
inline void mkBlackhole();
void mkPrimOp(PrimOp * p);
@ -447,6 +442,19 @@ public:
};
extern Value prim_blackHole;
inline bool Value::isBlackhole() const
{
return internalType == tApp && app.left == &prim_blackHole;
}
inline void Value::mkBlackhole()
{
mkApp(&prim_blackHole, &prim_blackHole);
}
#if HAVE_BOEHMGC
typedef std::vector<Value *, traceable_allocator<Value *>> ValueVector;
typedef std::map<Symbol, Value *, std::less<Symbol>, traceable_allocator<std::pair<const Symbol, Value *>>> ValueMap;