[Bug target/31420] New: CONSTRAINT_LEN is slow on i?86, x86_64

[rguenth at gcc dot gnu dot org]

For a -O0 tramp3d-v4.cpp compile, reload and its calls to CONSTRAINT_LEN are on
top of the profiles:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
 time   seconds   seconds    calls   s/call   s/call  name
  3.74      1.34     1.34   265677     0.00     0.00  record_reg_classes
  2.96      2.40     1.06  1145706     0.00     0.00  gt_ggc_mx_lang_tree_node
  2.62      3.34     0.94 10097098     0.00     0.00  ggc_alloc_stat
  2.51      4.24     0.90  2369119     0.00     0.00  walk_tree
  2.51      5.14     0.90   323915     0.00     0.00  find_reloads
  2.48      6.03     0.89 10110867     0.00     0.00 
expand_template_argument_pack
  2.29      6.85     0.82 33351577     0.00     0.00  lookup_constraint
  2.20      7.64     0.79 16245996     0.00     0.00  ggc_set_mark
  1.42      8.15     0.51  6300484     0.00     0.00  mark_set_1
  1.42      8.66     0.51   526692     0.00     0.00  retrieve_specialization
  1.14      9.07     0.41 32030410     0.00     0.00  insn_constraint_len

[42]     5.0    0.90    0.88  323915         find_reloads [42]
                0.45    0.00 18162825/33351577     lookup_constraint [68]
                0.23    0.00 17752937/32030410     insn_constraint_len [106]

At least insn_constraint_len could be inlined:

size_t
insn_constraint_len (enum constraint_num c)
{
  switch (c)
    {
    case CONSTRAINT_Y2: return 2;
    case CONSTRAINT_Yi: return 2;
    case CONSTRAINT_Ym: return 2;
    default: break;
    }
  return 1;
}

and both, insn_constraint_len and lookup_constraint can be marked pure.  For
i686 at least an optimized CONSTRAINT_LEN can be done with

#define CONSTRAINT_LEN(c_,s_) (c_ == 'Y' ? 2 : 1)


-- 
           Summary: CONSTRAINT_LEN is slow on i?86, x86_64
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: compile-time-hog
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org
GCC target triplet: i?86-*-* x86_64-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31420