Hi Jeff,
On 12/09/16 18:16, Jeff Law wrote:
On 09/05/2016 08:59 AM, Tamar Christina wrote:
Hi All,
This patch allows the FP register to be used as a call-saved
register when -fomit-frame-pointer is used.
The change is done in such a way that the defaults do not change.
To use the FP register both -fomit-frame-pointer and
-fcall-saved-<hard_fp_reg> need to be used.
Regression ran on aarch64-none-linux-gnu and no regressions.
Bootstrapped and ran regressions on `x86_64` and no regressions.
A new test fp_free_1 was added to test functionality.
Ok for trunk?
Thanks,
Tamar
PS. I don't have commit rights so if OK can someone apply the patch
for me.
gcc/
2016-09-01 Tamar Christina <tamar.christ...@arm.com>
* gcc/reginfo.c (fix_register): Allow FP to be set if
-fomit-frame-pointer.
I'm a little surprised you need this. Most ports allow use of FP as a
call-saved register with -fomit-frame-pointer.
I think this is because on most architectures the FP is not in the fixed
registers list. But the AArch64 ABI (I believe) currently
mandates that it is. With the option of:
- It may permit the frame pointer register to be used as a
general-purpose callee-saved register, but provide a platform-specific
mechanism for external agents to reliably detect this condition
- It may elect not to maintain a frame chain and to use the frame
pointer register as a general-purpose callee-saved register.
(from section 5.2.3 of the ABI).
In which case `-fomit-frame-pointer` alone won't be enough to use it as
a callee-saved register. I could try looking into alternatives if this
is a problem for other ports.
Also note the documentation explicitly forbids using -fcall-saved for
the stack or frame pointer.
Ah, yes, hadn't noticed that before. Isn't it a bit too strict a
restriction? In general if you have -fomit-frame-pointer then shouldn't
the it be safe for the FP to be used
with -fcall-saved? Since it's probably a no-op on most ports that
support -fomit-frame-pointer anyway?
Jeff
Regards,
Tamar
