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

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

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 9f83f366ab397589a1c1765ddc11bda78898603b..bb1d5d4083d943aa013fa7c80a7148553236a71a 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -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>
 

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 4b5df0b7edd03a8a969258dcf3432c73596e2968..e9d21a365ba88a645a3a44ee171bd84715f3b7d9 100644 (file)
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -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.