Re: [FORTRAN PATCH] Reduce gfc_match_strings usage (part 1)

[FX Coudert <fxcoudert at gmail dot com>]

Hi all,

A few days ago, I was wondering how much we could improve gfortran's  
compilation speed, and I built a compiler with profiling enabled (./ 
configure --disable-bootstrap CFLAGS=-pg LDFLAGS=-pg && make). On a - 
O0 compilation (the case where the front-end time is probably the  
most visible in the total compile time) of F95 intensive code (which  
is what tomorrow's code will look like; I chose CP2K for that  
fragment), the routines with >1% time are:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
time   seconds   seconds    calls   s/call   s/call  name
  6.81     15.41    15.41  4491770     0.00     0.00  walk_tree
  4.19     24.88     9.47 33123518     0.00     0.00  insert_aux
  4.09     34.13     9.25  6338750     0.00     0.00   
pointer_set_insert
  3.75     42.63     8.50  1103855     0.00     0.00  gfc_match_strings
  3.19     49.84     7.22 21693724     0.00     0.00   
generic_tree_operand
  2.26     54.96     5.12 33996539     0.00     0.00   
tree_operand_length
  2.13     59.77     4.81  1517589     0.00     0.00   
gt_ggc_mx_lang_tree_node
  1.82     63.89     4.12  9399814     0.00     0.00  ggc_set_mark
  1.66     67.65     3.76 33123518     0.00     0.00  hash1
  1.65     71.39     3.74   838706     0.00     0.00   
expand_expr_real_1
  1.54     74.88     3.49  3640277     0.00     0.00  ggc_alloc_stat
  1.49     78.24     3.36   925153     0.00     0.00  gimplify_expr
  1.23     81.03     2.79 16013192     0.00     0.00  next_char
  1.19     83.73     2.70   650548     0.00     0.00  operand_equal_p
  1.02     86.04     2.31 12717821     0.00     0.00   
gfc_next_char_literal

And if I only write out the Fortran front-end functions, the top of  
the list is:

  3.75     42.63     8.50  1103855     0.00     0.00  gfc_match_strings
  1.02     86.04     2.31 12717821     0.00     0.00   
gfc_next_char_literal
  0.29    127.21     0.65  7827668     0.00     0.00  gfc_next_char
  0.29    127.86     0.65  3191988     0.00     0.00   
gfc_gobble_whitespace
  0.28    129.13     0.64   631736     0.00     0.00  gfc_match
  0.23    141.23     0.52 13132866     0.00     0.00  gfc_at_end
  0.15    157.25     0.33    95191     0.00     0.00  gfc_advance_line
  0.15    157.58     0.33   296081     0.00     0.00  gfc_find_symtree
  0.12    164.39     0.28   954621     0.00     0.00  gfc_getmem
  0.11    165.19     0.26    58196     0.00     0.00  gfc_conv_variable
  0.11    166.20     0.25   217450     0.00     0.00  gfc_match_name
  0.11    166.45     0.25   353188     0.00     0.00  gfc_copy_expr


Anyone can draw his own conclusions, mine are that gfc_match_strings  
is indeed the spot where we spend most of our time (together with  
related routines like gfc_next_char*), but that only accounts for 5%  
of the compilation time. What I also see is that gfc_match_strings()  
is only called 3 times in the source, so that specialized  
replacements are probably not so bad a solution.


PS-1: My original idea was due to the recent patch about hot and cold  
attributes, and I wondered whether we could mark some gfc_ functions  
hot. I was about to suggest marking gfc_match_strings, gfc_next_char,  
gfc_next_char_literal and gfc_gobble_whitespace hot. What do you  
think about it?


PS-2: I also made a list of functions sorted by the number of times  
they get called:

13132866 0.23 gfc_at_end
12717821 1.02 gfc_next_char_literal
7827668 0.29 gfc_next_char
3191988 0.29 gfc_gobble_whitespace
1103855 3.75 gfc_match_strings
1041059 0.04 gfc_match_intrinsic_op
954621 0.12 gfc_getmem
755398 0.04 gfc_free
656869 0.05 gfc_clear_ts
631736 0.28 gfc_match
595726 0.04 gfc_free_expr
572279 0.06 gfc_simplify_expr
524067 0.07 gfc_get_expr

(number of times called / total time spent in that function /  
function name)

Seeing that, it appears there are very simple functions that are  
called very often. gfc_at_end(), for example, might be inline:
> int
> gfc_at_end (void)
> {
>   return end_flag;
> }
So can be gfc_getmem, gfc_free and. Maybe also gfc_clear_ts,  
gfc_get_expr and  gfc_free_expr?


FX