Re: disabling branch probability guessing (patch)

[Aldy Hernandez <aldyh at redhat dot com>]

On Tue, Jan 16, 2001 at 10:48:41PM -0800, Mark Mitchell wrote:
> 
> Thanks for posting this; it's a good summary, and sound logic.
> 
> I think it would be useful to have an even briefer summary in the
> code or info pages.  Something like:
> 
>   In a hard real-time system, people don't want different
>   runs of the compiler to produce code that has different behavior;
>   minimizing non-determinism is of paramount import.  This switch
>   allows users to reduce non-determinism, possibly at the expense
>   of inferior optimization.
> 
> Would you mind correcting and adding that somewhere?

not at all.

here is the updated patch.  I added your description to the info page.

i assume this is ok.
aldy

2001-01-16  Aldy Hernandez  <aldyh@redhat.com>

	* sourceware/gcc/gcc/invoke.texi (-fno-guess-branch-probability):
	New option.

Index: invoke.texi
===================================================================
RCS file: /cvs/gcc/egcs/gcc/invoke.texi,v
retrieving revision 1.262
diff -c -r1.262 invoke.texi
*** invoke.texi	2001/01/11 18:37:17	1.262
--- invoke.texi	2001/01/17 12:49:53
***************
*** 249,255 ****
  -finline-functions  -finline-limit=@var{n}  -fkeep-inline-functions
  -fkeep-static-consts  -fmove-all-movables
  -fno-default-inline  -fno-defer-pop
! -fno-function-cse  -fno-inline  -fno-math-errno  -fno-peephole
  -fomit-frame-pointer  -foptimize-register-move
  -foptimize-sibling-calls  -freduce-all-givs
  -fregmove  -frename-registers
--- 249,256 ----
  -finline-functions  -finline-limit=@var{n}  -fkeep-inline-functions
  -fkeep-static-consts  -fmove-all-movables
  -fno-default-inline  -fno-defer-pop
! -fno-function-cse  -fno-guess-branch-probability  -fno-inline 
! -fno-math-errno  -fno-peephole
  -fomit-frame-pointer  -foptimize-register-move
  -foptimize-sibling-calls  -freduce-all-givs
  -fregmove  -frename-registers
***************
*** 3090,3095 ****
--- 3091,3105 ----
  branch is mostly to take, the @samp{REG_BR_PROB} values are used to
  exactly determine which path is taken more often.
  @end ifset
+ 
+ @item -fno-guess-branch-probability
+ Sometimes gcc will opt to guess branch probabilities when none are
+ available from either profile directed feedback (@samp{-fprofile-arcs})
+ or @samp(__builtin_expect).  In a hard real-time system, people don't
+ want different runs of the compiler to produce code that has different
+ behavior; minimizing non-determinism is of paramount import.  This
+ switch allows users to reduce non-determinism, possibly at the expense
+ of inferior optimization.
  
  @item -fstrict-aliasing
  Allows the compiler to assume the strictest aliasing rules applicable to