| Message ID | AM4PR0802MB22740240D3C6DAED27731737FF130@AM4PR0802MB2274.eurprd08.prod.outlook.com |
|---|---|
| State | New |
| Headers | show |
On 08/16/2016 08:01 AM, Tamar Christina wrote: > > Hi All, > > This patch turns off the usage of section anchors for > declarations that do not fit in a single anchor range. > A large enough object will use the full anchor range > and also force the use of another anchor pointer. > > By not using an anchor for large objects more globals > can share the same anchor. > > The patch has been benchmarked using Spec2000 and > the impact on performance is negligible, however some files > using large arrays showed a appreciable reduction in amount of > instructions in the assembly file. > > Regression tests were run on aarch64-none-elf and no regressions. > > Ok for trunk? > > 2016-08-16 Tamar Christina <tamar.christina@arm.com> > Ramana Radhakrishnan <ramana.radhakrishnan@arm.com> > > * gcc/varasm.c > (default_use_anchors_for_symbol_p): Reject too large decls. Do you have to worry about DECL_SIZE being non-constant here or are those filtered out earlier? jeff
On Tue, Aug 16, 2016 at 6:06 PM, Jeff Law <law@redhat.com> wrote: > On 08/16/2016 08:01 AM, Tamar Christina wrote: >> >> >> Hi All, >> >> This patch turns off the usage of section anchors for >> declarations that do not fit in a single anchor range. >> A large enough object will use the full anchor range >> and also force the use of another anchor pointer. >> >> By not using an anchor for large objects more globals >> can share the same anchor. >> >> The patch has been benchmarked using Spec2000 and >> the impact on performance is negligible, however some files >> using large arrays showed a appreciable reduction in amount of >> instructions in the assembly file. >> >> Regression tests were run on aarch64-none-elf and no regressions. >> >> Ok for trunk? >> >> 2016-08-16 Tamar Christina <tamar.christina@arm.com> >> Ramana Radhakrishnan <ramana.radhakrishnan@arm.com> >> >> * gcc/varasm.c >> (default_use_anchors_for_symbol_p): Reject too large decls. > > Do you have to worry about DECL_SIZE being non-constant here or are those > filtered out earlier? Globals can't have variable size. Richard. > jeff
On 17/08/16 09:23, Richard Biener wrote: > On Tue, Aug 16, 2016 at 6:06 PM, Jeff Law <law@redhat.com> wrote: >> On 08/16/2016 08:01 AM, Tamar Christina wrote: >>> >>> >>> Hi All, >>> >>> This patch turns off the usage of section anchors for >>> declarations that do not fit in a single anchor range. >>> A large enough object will use the full anchor range >>> and also force the use of another anchor pointer. >>> >>> By not using an anchor for large objects more globals >>> can share the same anchor. >>> >>> The patch has been benchmarked using Spec2000 and >>> the impact on performance is negligible, however some files >>> using large arrays showed a appreciable reduction in amount of >>> instructions in the assembly file. >>> >>> Regression tests were run on aarch64-none-elf and no regressions. >>> >>> Ok for trunk? >>> >>> 2016-08-16 Tamar Christina <tamar.christina@arm.com> >>> Ramana Radhakrishnan <ramana.radhakrishnan@arm.com> >>> >>> * gcc/varasm.c >>> (default_use_anchors_for_symbol_p): Reject too large decls. >> >> Do you have to worry about DECL_SIZE being non-constant here or are those >> filtered out earlier? > > Globals can't have variable size. > And Common variables (which may change size at link time) can't go in anchor groups. Nor, for that matter, can anything that's preemtible at link time. R. > Richard. > >> jeff >
On 08/17/2016 02:23 AM, Richard Biener wrote: > On Tue, Aug 16, 2016 at 6:06 PM, Jeff Law <law@redhat.com> wrote: >> On 08/16/2016 08:01 AM, Tamar Christina wrote: >>> >>> >>> Hi All, >>> >>> This patch turns off the usage of section anchors for >>> declarations that do not fit in a single anchor range. >>> A large enough object will use the full anchor range >>> and also force the use of another anchor pointer. >>> >>> By not using an anchor for large objects more globals >>> can share the same anchor. >>> >>> The patch has been benchmarked using Spec2000 and >>> the impact on performance is negligible, however some files >>> using large arrays showed a appreciable reduction in amount of >>> instructions in the assembly file. >>> >>> Regression tests were run on aarch64-none-elf and no regressions. >>> >>> Ok for trunk? >>> >>> 2016-08-16 Tamar Christina <tamar.christina@arm.com> >>> Ramana Radhakrishnan <ramana.radhakrishnan@arm.com> >>> >>> * gcc/varasm.c >>> (default_use_anchors_for_symbol_p): Reject too large decls. >> >> Do you have to worry about DECL_SIZE being non-constant here or are those >> filtered out earlier? > > Globals can't have variable size. Duh. You're obviously correct. Patch is OK for the trunk. jeff
On Wed, Aug 17, 2016 at 09:09:07PM -0600, Jeff Law wrote: > On 08/17/2016 02:23 AM, Richard Biener wrote: > >On Tue, Aug 16, 2016 at 6:06 PM, Jeff Law <law@redhat.com> wrote: > >>On 08/16/2016 08:01 AM, Tamar Christina wrote: > >>> > >>> > >>>Hi All, > >>> > >>>This patch turns off the usage of section anchors for > >>>declarations that do not fit in a single anchor range. > >>>A large enough object will use the full anchor range > >>>and also force the use of another anchor pointer. > >>> > >>>By not using an anchor for large objects more globals > >>>can share the same anchor. > >>> > >>>The patch has been benchmarked using Spec2000 and > >>>the impact on performance is negligible, however some files > >>>using large arrays showed a appreciable reduction in amount of > >>>instructions in the assembly file. > >>> > >>>Regression tests were run on aarch64-none-elf and no regressions. > >>> > >>>Ok for trunk? > >>> > >>>2016-08-16 Tamar Christina <tamar.christina@arm.com> > >>> Ramana Radhakrishnan <ramana.radhakrishnan@arm.com> > >>> > >>> * gcc/varasm.c > >>> (default_use_anchors_for_symbol_p): Reject too large decls. > >> > >>Do you have to worry about DECL_SIZE being non-constant here or are those > >>filtered out earlier? > > > >Globals can't have variable size. > Duh. You're obviously correct. > > Patch is OK for the trunk. Tamar's not yet got commit rights, so I've committed this on his behalf as r239561. Thanks for the review! James
:100644 100644 e747d2c... 00a9b30... M gcc/varasm.c diff --git a/gcc/varasm.c b/gcc/varasm.c index e747d2c..00a9b30 100644 --- a/gcc/varasm.c +++ b/gcc/varasm.c @@ -6793,6 +6793,15 @@ default_use_anchors_for_symbol_p (const_rtx symbol) sections that should be marked as small in the section directive. */ if (targetm.in_small_data_p (decl)) return false; + + /* Don't use section anchors for decls that won't fit inside a single + anchor range to reduce the amount of instructions require to refer + to the entire declaration. */ + if (decl && DECL_SIZE (decl) + && tree_to_shwi (DECL_SIZE (decl)) + >= (targetm.max_anchor_offset * BITS_PER_UNIT)) + return false; + } return true; }