On 09/13/2016 05:10 AM, Tamar Christina wrote:
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.
So those don't seem to me to imply that the frame pointer needs to be a
fixed register. So the first thing I'd do is fix the aarch64 port to
not do that and see what fallout there is and how to fix it.
Most ports simply don't mark the frame pointer as fixed.
I am a bit curious about how you're going to solve the "external agents
to reliably detect this condition" :-)
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?
It might be. In general I don't think the -fcall-whatever options are
used that much anymore and I don't think anyone has seriously looked at
their documentation in a long time.
Regardless, I still think the first step is to "unfix" the frame pointer
hard register on the aarch64 port.
jeff
