mkList: Scrub better

Clearing v.app.right was not enough, because the length field of a
list only takes 32 bits, so the most significant 32 bits of v.app.left
(a.k.a. v.thunk.env) would remain. This could cause Boehm GC to
interpret it as a valid pointer.

This change reduces maximum RSS for evaluating the ‘tested’ job in
nixos/release-small.nix from 1.33 GiB to 0.80 GiB, and runtime by
about 8%.
This commit is contained in:
Eelco Dolstra 2014-10-09 13:08:53 +02:00
parent 986fbd6fab
commit 6bb4c0b712
2 changed files with 3 additions and 2 deletions

View file

@ -455,6 +455,7 @@ Bindings * EvalState::allocBindings(Bindings::size_t capacity)
void EvalState::mkList(Value & v, unsigned int length) void EvalState::mkList(Value & v, unsigned int length)
{ {
clearValue(v);
v.type = tList; v.type = tList;
v.list.length = length; v.list.length = length;
v.list.elems = length ? (Value * *) GC_MALLOC(length * sizeof(Value *)) : 0; v.list.elems = length ? (Value * *) GC_MALLOC(length * sizeof(Value *)) : 0;

View file

@ -96,7 +96,7 @@ struct Value
Value to ensure that the target isn't kept alive unnecessarily. */ Value to ensure that the target isn't kept alive unnecessarily. */
static inline void clearValue(Value & v) static inline void clearValue(Value & v)
{ {
v.app.right = 0; v.app.left = v.app.right = 0;
} }
@ -118,8 +118,8 @@ static inline void mkBool(Value & v, bool b)
static inline void mkNull(Value & v) static inline void mkNull(Value & v)
{ {
clearValue(v);
v.type = tNull; v.type = tNull;
v.app.left = v.app.right = 0; // scrub
} }