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Re: ARM r12 usage
- To: armcc at lycos dot com
- Subject: Re: ARM r12 usage
- From: Richard Earnshaw <rearnsha at arm dot com>
- Date: Mon, 12 Mar 2001 10:00:58 +0000
- cc: gcc at gcc dot gnu dot org, Richard dot Earnshaw at arm dot com
- Organization: ARM Ltd.
- Reply-To: Richard dot Earnshaw at arm dot com
> When using -fomit-frame-pointer with arm-elf-gcc v2.95.2, it seems
> that r11 doesn't get used at all ??
>
> Is this correct ? (If so why ?) Or have I missed something again :-)
Gcc has to hold r11 (fp) in reserve during the initial register allocation
in case it is needed as a frame pointer (some functions still require one
even with -fomit-frame-pointer). At times it is not very good at making
use of the register once it has determined that it doesn't require it for
other purposes.
Note that in gcc-3.0 (and the current snapshots) you will have to use the
option -mno-apcs-frame to omit the frame pointer from all functions. When
optimizing the new compiler will automatically try to eliminate the frame
pointer from all leaf functions even if -fomit-frame-pointer is not
requested.
R.