[Bug tree-optimization/114711] New: Missed optimization: fold load of global constant array if there is obivous pattern

[Bug tree-optimization/114711] New: Missed optimization: fold load of global constant array if there is obivous pattern

[xxs_chy at outlook dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114711

            Bug ID: 114711
           Summary: Missed optimization: fold load of global constant
                    array if there is obivous pattern
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xxs_chy at outlook dot com
  Target Milestone: ---

Godbolt link: https://godbolt.org/z/MMxoGaj9T

```
static char* const names[3] = {"abc", "cdf", "dsadsa"};
char** const id2name[3] = {names, names + 1, names + 2};

void* src(size_t idx){
    return id2name[idx];
}

```

can be folded to:

```
static char* const names[3] = {"abc", "cdf", "dsadsa"};
void* tgt(size_t idx){
    return names + idx;
}
```

This is a real pattern from openssl.

[Bug tree-optimization/114711] Missed optimization: fold load of global constant array if there is obivous pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114711

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=114682

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note the openssl code issue was reported in pr 114682

[Bug tree-optimization/114711] Missed optimization: fold load of global constant array if there is obivous pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114711

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |missed-optimization
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-04-13
           Severity|normal                      |enhancement

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
In the openssl code, it is a loop which can be unrolled and gcc does and then
is able to handle the load for string just fine but not the resulting ID. See
the linked issue for that.


But confirmed on this one but it is definitely harder.

[Bug tree-optimization/114711] Missed optimization: fold load of global constant array if there is obivous pattern

[xxs_chy at outlook dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114711

--- Comment #3 from XChy <xxs_chy at outlook dot com> ---
(In reply to Andrew Pinski from comment #1)
> Note the openssl code issue was reported in pr 114682

Oh, thanks for transferring this LLVM issue! And because I'm recently trying to
transfer some of my LLVM issues to GCC and do some statistic work, let me know
if you have transferred some of them.

[Bug tree-optimization/114711] Missed optimization: fold load of global constant array if there is obivous pattern

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114711

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
This one requires "symbolicizing" an initializer.  That might for example also
help implementing a non-constant initializer with a loop, reducing .data and
possibly relocations.  It might also help reducing compile-time memory usage
when we can have a more compact representation of a CONSTRUCTOR and its
elements.

It feels somewhat similar to what we do in switch-conversion, so maybe some
common infrastructure could be built.