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patch to remove temporary clobbers in LRA
- From: Vladimir Makarov <vmakarov at redhat dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Sun, 28 Oct 2012 16:06:23 -0400
- Subject: patch to remove temporary clobbers in LRA
Working on a problem where var-tracking started to spend more time
after LRA is switched on, I found that LRA creates significant #
clobbers for x86 code (I saw 20% of all insns). Clobbers are created for
correct live range analysis in LRA in cases when matching pseudos of
*different modes* should be in the same hard register.
As these clobbers are not needed anymore after LRA, the following
patch removes them.
Unfortunately, it does not solve the problem I mentioned. Now, LRA
generates approximately the same # of insns and debug_insn. Moreover,
two functions (canonicalize_values_star and set_slot_part) in
var-tracking spending most of time have approximately the same coverage,
in other words numbers of execution for each line are the same
(differences < 1%). Still var-tracking after LRA spent on 20% more time
than after reload. I have no idea what to investigate more but I'll
continue my work on the problem next week.
The patch was successfully bootstrapped on x86/x86-64.
Committed as rev. 192897.
2012-10-28 Vladimir Makarov <firstname.lastname@example.org>
* rtl.h (struct rtx_def): Add a comment for member unchanging.
* lra-int.h (LRA_TEMP_CLOBBER_P): New macro.
(lra_hard_reg_substitution): Rename to lra_final_code_change.
* lra-constraints.c (match_reload): Mark temporary clobbers.
* lra-spill.c (lra_hard_reg_substitution): Rename to
lra_final_code_change. Remove temporary clobbers.
* lra.c (lra): Rename to lra_final_code_change.
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