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PR 161/251 patch causing massive link time regression

H. J. Lu hjl@lucon.org
Thu Oct 14 18:48:00 GMT 2004 
On Thu, Oct 14, 2004 at 02:56:26PM +0200, Jakub Jelinek wrote:
> On Wed, Oct 13, 2004 at 05:21:07PM -0700, H. J. Lu wrote:
> > It should help. We can also require the single member comdat group,
> > which may match a linkonce section, should have the group sigature
> > the same as the section name of the linkonce section. We don't have
> > to check symbols between 2 sections.
> > 
> > BTW, the problem my patch tries to fix is
> > 
> > 	.section .gnu.linkonce.t.__i686.get_pc_thunk.bx,"axG",@progbits,__i686.get_pc_thunk.bx,comdat
> > 
> > vs.
> > 
> >         .section .gnu.linkonce.t.__i686.get_pc_thunk.bx,"ax",@progbits
> > 
> > linker should treat them the same. If gcc can generate
> > 
> > 	.section .gnu.linkonce.t.__i686.get_pc_thunk.bx,"axG",@progbits,.gnu.linkonce.t.__i686.get_pc_thunk.bx,comdat
> > 
> > it will help linker a lot.
> 
> Would the following patch be enough?
> 
> E.g. following combinations would work:
> .section .gnu.linkonce.t.__i686.get_pc_thunk.bx,"axG",@progbits,__i686.get_pc_thunk.bx,comdat
> .section .gnu.linkonce.t.__i686.get_pc_thunk.bx,"ax",@progbits
> 
> .section .gnu.linkonce.t.__i686.get_pc_thunk.bx,"axG",@progbits,.gnu.linkonce.t.__i686.get_pc_thunk.bx,comdat
> .section .gnu.linkonce.t.__i686.get_pc_thunk.bx,"ax",@progbits
> 
> .section .text,"axG",@progbits,__i686.get_pc_thunk.bx,comdat
> .section .gnu.linkonce.t.__i686.get_pc_thunk.bx,"ax",@progbits
> 
> .section .text,"axG",@progbits,.gnu.linkonce.t.__i686.get_pc_thunk.bx,comdat
> .section .gnu.linkonce.t.__i686.get_pc_thunk.bx,"ax",@progbits
> 
> though your testcase in PR 161 will not work (the comdat group is there
> .__i686.get_pc_thunk.bx, not sure why the dot at the begining).

It is OK. We can put restriction on group signature when it should
match a linkonce section.

> At least the intent of the patch (unless I goofed up) is doing exactly what
> linker did without this patch, but only try to match sections that have the
> same base section name (resp. comdat group name), where base section name
> is section name with ^\.gnu\.linkonce\.[^.]*\. prefix if present stripped.
> 

It looks good to me. How much speed up did yot get with it?


H.J.
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