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Re: [PATCH][C++] Save memory/time when folding CONSTRUCTORs
On Wed, 1 Feb 2017, Nathan Sidwell wrote:
> On 02/01/2017 09:03 AM, Richard Biener wrote:
> >
> > Currently we copy CONSTRUCTORs we cp_fold even if no elements fold
> > (we throw the copy away then). That's wasteful and we can easily
> > do the copying on-demand. For simplicity the following resorts
> > to memcpy-ing the whole original vector on the first change
> > and only overwrites changed elements in the folding loop
> > (I suspect that's usually faster given initializer elements do
> > usually not fold(?)).
> >
> > That removes another 35MB GC memory use from the PR12245 testcase.
> > (the biggest offender there is, non-surprisingly the C++ preprocessor
> > tokens with 130MB followed by 35MB for the CONSTRUCTOR and 40MB for
> > INTEGER_CSTs).
> >
> > Bootstrap / regtest running on x86_64-unknown-linux-gnu.
> >
> > Ok for trunk if that succeeds?
> >
> > Thanks,
> > Richard.
> >
> > 2017-02-01 Richard Biener <rguenther@suse.de>
> >
> > PR cp/14179
> > cp/
> > * cp-gimplify.c (cp_fold): When folding a CONSTRUCTOR copy
> > it lazily on the first changed element only and copy it
> > fully upfront, only storing changed elements.
> >
> > Index: gcc/cp/cp-gimplify.c
> > ===================================================================
> > --- gcc/cp/cp-gimplify.c (revision 245094)
> > +++ gcc/cp/cp-gimplify.c (working copy)
> > @@ -2361,12 +2361,9 @@ cp_fold (tree x)
> > bool changed = false;
> > vec<constructor_elt, va_gc> *elts = CONSTRUCTOR_ELTS (x);
> > vec<constructor_elt, va_gc> *nelts = NULL;
>
> > + if (! changed)
> > + {
> > + nelts = elts->copy ();
> > + changed = true;
> > + }
>
> doesn't this make 'changed' a synonym for 'nelts != NULL'? (so you could
> ditch the former)
True. Updated patch below.
Richard.
2017-02-01 Richard Biener <rguenther@suse.de>
PR cp/14179
cp/
* cp-gimplify.c (cp_fold): When folding a CONSTRUCTOR copy
it lazily on the first changed element only and copy it
fully upfront, only storing changed elements.
Index: gcc/cp/cp-gimplify.c
===================================================================
--- gcc/cp/cp-gimplify.c (revision 245096)
+++ gcc/cp/cp-gimplify.c (working copy)
@@ -2358,15 +2358,11 @@ cp_fold (tree x)
{
unsigned i;
constructor_elt *p;
- bool changed = false;
vec<constructor_elt, va_gc> *elts = CONSTRUCTOR_ELTS (x);
vec<constructor_elt, va_gc> *nelts = NULL;
- vec_safe_reserve (nelts, vec_safe_length (elts));
FOR_EACH_VEC_SAFE_ELT (elts, i, p)
{
tree op = cp_fold (p->value);
- constructor_elt e = { p->index, op };
- nelts->quick_push (e);
if (op != p->value)
{
if (op == error_mark_node)
@@ -2375,10 +2371,12 @@ cp_fold (tree x)
changed = false;
break;
}
- changed = true;
+ if (nelts == NULL)
+ nelts = elts->copy ();
+ (*nelts)[i].value = op;
}
}
- if (changed)
+ if (nelts)
x = build_constructor (TREE_TYPE (x), nelts);
else
vec_free (nelts);