[Bug middle-end/63556] New: gcc should dedup string postfixes

[Bug middle-end/63556] New: gcc should dedup string postfixes

[andi-gcc at firstfloor dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

            Bug ID: 63556
           Summary: gcc should dedup string postfixes
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: andi-gcc at firstfloor dot org

With this code:

extern void func(char *a, char *b);

void f(void)
{
        func("abc", "xabc");
        func("abc", "abc");
}

we get:

.LC0:
        .string "xabc"
.LC1:
        .string "abc"

So the "abc"s get deduped. But it could also dedup the postfix by pointing
"abc" to "xabc" + 1. This would save some space.

[Bug middle-end/63556] gcc should dedup string postfixes

[andi-gcc at firstfloor dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

Andi Kleen <andi-gcc at firstfloor dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug middle-end/63556] gcc should dedup string postfixes

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-10-16
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Constant/literal pool also misses merging V2DF { 0., 0. } with
DF 0. for example (and more).  There's another PR for that somewhere with
some hackish patch from me.

[Bug middle-end/63556] gcc should dedup string postfixes

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

--- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> ---
This is done by the linker, as part of the merge section handling.

Contents of section .rodata:
 4005b0 01000200 78616263 00                 ....xabc.

[Bug middle-end/63556] gcc should dedup string postfixes

[andi-gcc at firstfloor dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

Andi Kleen <andi-gcc at firstfloor dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|NEW                         |RESOLVED

--- Comment #3 from Andi Kleen <andi-gcc at firstfloor dot org> ---
Since the linker does it the change is not needed.

[Bug middle-end/63556] gcc should dedup string postfixes

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|WONTFIX                     |---
                 CC|                            |xry111 at gcc dot gnu.org
             Status|RESOLVED                    |REOPENED

--- Comment #4 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Added the gentleman applying as the new IA64 maintainer into CC and reopened.

[Bug middle-end/63556] gcc should dedup string postfixes

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #5 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Sorry somehow changed the wrong bug.  I don't really understand the rule of
bugzilla for jumping into another bug when I changed one...

[Bug middle-end/63556] gcc should dedup string postfixes

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
When you touch this, only ld.bfd does this optimization, none of gold, lld or
mold (at least versions I've tried) do that.  Easy way to speed up the
linkers...

[Bug middle-end/63556] gcc should dedup string postfixes

[andi-gcc at firstfloor dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

--- Comment #7 from Andi Kleen <andi-gcc at firstfloor dot org> ---
I'm not sure how it would speed up the linker if gcc did it. The linker would
still need to do it because there might be matches between different .o files.
Also linker wouldn't know if the compiler supported this or not.

[Bug middle-end/63556] gcc should dedup string postfixes

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63556

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andi Kleen from comment #7)
> I'm not sure how it would speed up the linker if gcc did it. The linker
> would still need to do it because there might be matches between different
> .o files. Also linker wouldn't know if the compiler supported this or not.

I think you misunderstood Jakub's comment, he was basically mentioning that
comparing the linking speed of gold/mold/lld to bfd ld is not exactly fair
because those don't implement this optimization. Removing it from bfd ld might
speed up it up too. It was not really a comment about adding it to GCC.