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Merge pull request #5809 from pennae/small-perf-improvements

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small perf improvements
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Théophane Hufschmitt 2021-12-21 08:50:29 +01:00 committed by GitHub
parent 6e6e998930 09b245690a
commit de273bbff2
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GPG key ID: 4AEE18F83AFDEB23
2 changed files with 19 additions and 1 deletions
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17
src/libexpr/eval.cc
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@ -821,8 +821,23 @@ inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
Value * EvalState::allocValue()
{
/* We use the boehm batch allocator to speed up allocations of Values (of which there are many).
GC_malloc_many returns a linked list of objects of the given size, where the first word
of each object is also the pointer to the next object in the list. This also means that we
have to explicitly clear the first word of every object we take. */
if (!valueAllocCache) {
valueAllocCache = GC_malloc_many(sizeof(Value));
if (!valueAllocCache) throw std::bad_alloc();
}
/* GC_NEXT is a convenience macro for accessing the first word of an object.
Take the first list item, advance the list to the next item, and clear the next pointer. */
void * p = valueAllocCache;
GC_PTR_STORE_AND_DIRTY(&valueAllocCache, GC_NEXT(p));
GC_NEXT(p) = nullptr;
nrValues++;
auto v = (Value *) allocBytes(sizeof(Value));
auto v = (Value *) p;
return v;
}

3
src/libexpr/eval.hh
View file

@ -133,6 +133,9 @@ private:
/* Cache used by prim_match(). */
std::shared_ptr<RegexCache> regexCache;
/* Allocation cache for GC'd Value objects. */
void * valueAllocCache = nullptr;
public:
EvalState(