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PR rtl-optimization/19705 - -fno-branch-count-reg doesn't prevent decrement

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PR rtl-optimization/19705 - -fno-branch-count-reg doesn't prevent decrement
	and branch instructions on a count register

gcc/ChangeLog:
2016-03-07  Martin Sebor  <msebor@redhat.com>

	PR rtl-optimization/19705
	* doc/invoke.texi (Options That Control Optimization): Clarify
	-fno-branch-count-reg.

From-SVN: r234039
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Martin Sebor 2016-03-07 17:10:12 +00:00 • committed by Martin Sebor
parent dbb23418b2
commit 92f87f08e6
2 changed files with 14 additions and 5 deletions
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gcc/ChangeLog
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@ -1,3 +1,9 @@
2016-03-07 Martin Sebor <msebor@redhat.com>
PR rtl-optimization/19705
* doc/invoke.texi (Options That Control Optimization): Clarify
-fno-branch-count-reg.
2016-02-26 Richard Biener <rguenther@suse.de>
Jeff Law <law@redhat.com>

13
gcc/doc/invoke.texi
View file

@ -6541,11 +6541,14 @@ life-range analysis. This option is effective only with
@item -fno-branch-count-reg
@opindex fno-branch-count-reg
Do not use ``decrement and branch'' instructions on a count register,
but instead generate a sequence of instructions that decrement a
register, compare it against zero, then branch based upon the result.
This option is only meaningful on architectures that support such
instructions, which include x86, PowerPC, IA-64 and S/390.
Avoid running a pass scanning for opportunities to use ``decrement and
branch'' instructions on a count register instead of generating sequences
of instructions that decrement a register, compare it against zero, and
then branch based upon the result. This option is only meaningful on
architectures that support such instructions, which include x86, PowerPC,
IA-64 and S/390. Note that the @option{-fno-branch-count-reg} option
doesn't remove the decrement and branch instructions from the generated
instruction stream introduced by other optimization passes.
Enabled by default at @option{-O1} and higher.