Default -fomit-frame-pointer for PowerPC

[Finkel, Hal J. via cfe-commits]

On 4/2/19 12:31 PM, Roman Lebedev via cfe-commits wrote:
> Best to submit patches to phabricator https://reviews.llvm.org/


Please follow the instructions here:
http://llvm.org/docs/Phabricator.html#requesting-a-review-via-the-web-interface
- This will make it much easier for us to track this.

Thanks!

 -Hal

>
> On Tue, Apr 2, 2019 at 8:30 PM George Koehler via cfe-commits
> <cfe-commits at lists.llvm.org> wrote:
>> Hello cfe-commits,
>>
>> The attached patch is for clang to use -fomit-frame-pointer by default
>> for all PowerPC targets when optimizing code.  Right now, clang uses
>> -fomit-frame-pointer for PowerPC Linux and NetBSD but not for other
>> targets.  I have been running `clang -target powerpc-openbsd`.
>>
>> The patch is for llvm-project.git master.  I previously posted this
>> patch to https://bugs.llvm.org/show_bug.cgi?id=41094 , but the patch
>> in this email is for a newer revision of master.
>>
>> In most functions, the frame pointer in r31 is an unnecessary extra
>> copy of the stack pointer in r1.  GCC is using -fomit-frame-pointer by
>> default (in my PowerPC machine running OpenBSD/macppc); I want Clang
>> to be at least as good as GCC.  Also, this patch helps me to compare
>> the output of `clang -target powerpc-openbsd -O2 -S` with the output
>> for Linux or NetBSD.  In bug 41094, I showed how -fomit-frame-pointer
>> simplifies the C function `void nothing(void) {}`.
>>
>> This is my first mail to cfe-commits; I'm using the instructions at
>> http://llvm.org/docs/DeveloperPolicy.html#making-and-submitting-a-patch
>>
>> --
>> George Koehler <kernigh at gmail.com>
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory