PATCH: Expose MAX_PASSES in gcse.c to command line

[Brad Lucier <lucier at math dot purdue dot edu>]

The following patch changes the macro MAX_PASSES in gcse.c to a
variable that can be controlled by a -fgcse-limit= command-line
switch.

I wanted this to make it easier to experiment with the number of
passes.  For example, with the file I'm using to test the correctness
of gcse right now, I get with

../../gcc/objdir/gcc/cc1 -O2 -fno-math-errno -mcpu=ev6 -mieee -fgcse-limit=3 -da -gstabs _io.i

the following

% grep pass *08*
GCSE pass 1
CPROP of ___H__20___io, pass 1: 1637953 bytes needed, 1 const props, 10 copy props
PRE GCSE of ___H__20___io, pass 1: 2914017 bytes needed, 110 substs, 3156 insns created
GCSE pass 2
CPROP of ___H__20___io, pass 2: 1777907 bytes needed, 3 const props, 116 copy props
PRE GCSE of ___H__20___io, pass 2: 3082083 bytes needed, 1689 substs, 94 insns created
GCSE pass 3
CPROP of ___H__20___io, pass 3: 1821076 bytes needed, 3 const props, 492 copy props
PRE GCSE of ___H__20___io, pass 3: 3047436 bytes needed, 2 substs, 1 insns created
CPROP of ___H__20___io, pass 4: 4900524 bytes needed, 2 const props, 0 copy props
GCSE of ___H__20___io: 7016 basic blocks, 3 passes, 3632443 bytes

so there are many more copy props in later passes than in the first.

This bootstraps on alphaev6-unknown-linux-gnu with BOOT_CFLAGS='-O2 -g -fgcse-limit=3' and no regressions with

make -k check RUNTESTFLAGS="--tool_opts '-fgcse-limit=3'" > & check.log

Brad Lucier

	* gcse.c (gcse_max_passes): Introduce new global. Use it.
	* flags.h (gcse_max_passes): Declare it.
	* toplev.c (-fgcse-limit=): Introduce new flag.
	* invoke.texi (-fgcse-limit=): Document it.

===================================================================
RCS file: RCS/flags.h,v
retrieving revision 1.1
diff -cp -r1.1 flags.h
*** flags.h	2000/11/30 19:39:25	1.1
--- flags.h	2000/11/30 19:40:31
*************** extern int g_switch_set;
*** 572,577 ****
--- 572,581 ----
  
  extern int inline_max_insns;
  
+ /* Value of the -fgcse-limit flag.  */
+ 
+ extern int gcse_max_passes;
+ 
  /* Values of the -falign-* flags: how much to align labels in code. 
     0 means `use default', 1 means `don't align'.  
     For each variable, there is an _log variant which is the power
===================================================================
RCS file: RCS/gcse.c,v
retrieving revision 1.1
diff -cp -r1.1 gcse.c
*** gcse.c	2000/11/30 19:40:36	1.1
--- gcse.c	2000/11/30 19:42:55
*************** Boston, MA 02111-1307, USA.  */
*** 165,171 ****
  #define obstack_chunk_free free
  
  /* Maximum number of passes to perform.  */
! #define MAX_PASSES 1
  
  /* Propagate flow information through back edges and thus enable PRE's
     moving loop invariant calculations out of loops.
--- 165,172 ----
  #define obstack_chunk_free free
  
  /* Maximum number of passes to perform.  */
! 
! int gcse_max_passes = 1;
  
  /* Propagate flow information through back edges and thus enable PRE's
     moving loop invariant calculations out of loops.
*************** Boston, MA 02111-1307, USA.  */
*** 230,237 ****
     substitutions.
  
     PRE is quite expensive in complicated functions because the DFA can take
!    awhile to converge.  Hence we only perform one pass.  Macro MAX_PASSES can
!    be modified if one wants to experiment.
  
     **********************
  
--- 231,238 ----
     substitutions.
  
     PRE is quite expensive in complicated functions because the DFA can take
!    awhile to converge.  Hence we only perform one pass.  Flag -fgcse-limit can
!    be set if one wants to experiment.
  
     **********************
  
*************** gcse_main (f, file)
*** 719,725 ****
    max_pass_bytes = 0;
    gcse_obstack_bottom = gcse_alloc (1);
    changed = 1;
!   while (changed && pass < MAX_PASSES)
      {
        changed = 0;
        if (file)
--- 720,726 ----
    max_pass_bytes = 0;
    gcse_obstack_bottom = gcse_alloc (1);
    changed = 1;
!   while (changed && pass < gcse_max_passes)
      {
        changed = 0;
        if (file)
===================================================================
RCS file: RCS/invoke.texi,v
retrieving revision 1.1
diff -cp -r1.1 invoke.texi
*** invoke.texi	2000/11/30 19:46:44	1.1
--- invoke.texi	2000/11/30 19:49:51
*************** in the following sections.
*** 190,196 ****
  -fexpensive-optimizations  -ffast-math  -ffloat-store
  -fforce-addr  -fforce-mem  -ffunction-sections  -fgcse 
  -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
--- 190,196 ----
  -fexpensive-optimizations  -ffast-math  -ffloat-store
  -fforce-addr  -fforce-mem  -ffunction-sections  -fgcse 
  -finline-functions  -finline-limit=@var{n}  -fkeep-inline-functions
! -fgcse-limit=@var{n} -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
*************** Even if all calls to a given function ar
*** 2768,2773 ****
--- 2768,2778 ----
  is declared @code{static}, nevertheless output a separate run-time
  callable version of the function.  This switch does not affect
  @code{extern inline} functions.
+ 
+ @item -fgcse-limit=@var{n}
+ By default, GCC runs the gcse pass once.  Setting this parameter
+ to a higher value will allow more iterations of the gcse pass,
+ possibly leading to better optimization.
  
  @item -fkeep-static-consts
  Emit variables declared @code{static const} when optimization isn't turned
===================================================================
RCS file: RCS/toplev.c,v
retrieving revision 1.1
diff -cp -r1.1 toplev.c
*** toplev.c	2000/11/30 19:38:18	1.1
--- toplev.c	2000/11/30 19:44:30
*************** decode_f_option (arg)
*** 4054,4059 ****
--- 4054,4062 ----
    else if ((option_value = skip_leading_substring (arg, "sched-verbose=")))
      fix_sched_param ("verbose", option_value);
  #endif
+   else if ((option_value = skip_leading_substring (arg, "gcse-limit=")))
+     gcse_max_passes
+       = read_integral_parameter (option_value, arg - 2, gcse_max_passes);
    else if ((option_value = skip_leading_substring (arg, "fixed-")))
      fix_register (option_value, 1, 1);
    else if ((option_value = skip_leading_substring (arg, "call-used-")))