[Bug tree-optimization/83491] [8 Regression] ICE in execute_cse_reciprocals_1 at gcc/tree-ssa-math-opts.c:585

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83491

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
There are multiple bugs:
1) the callers of execute_cse_reciprocals_1 ensure that def is SSA_NAME, so
using:
  /* If this is a square (x * x), we should check whether there are any
     enough divisions by x on it's own to warrant waiting for that pass.  */
  if (TREE_CODE (def) == SSA_NAME)
    {
      gimple *def_stmt = SSA_NAME_DEF_STMT (def);
...
    }

  FOR_EACH_IMM_USE_FAST (use_p, use_iter, def)
    {
      gimple *use_stmt = USE_STMT (use_p);
is misleading.  The thing is, the FOR_EACH_IMM_USE_FAST would fail miserably if
def isn't SSA_NAME.  Please just add gcc_checking_assert (TREE_CODE (def) ==
SSA_NAME); or gcc_assert, and reindent the body of the useless first if.

2)
      if (is_gimple_assign (def_stmt)
          && gimple_assign_rhs_code (def_stmt) == MULT_EXPR
          && gimple_assign_rhs1 (def_stmt) == gimple_assign_rhs2 (def_stmt))
This of course needs to also verify that TREE_CODE (gimple_assign_rhs1
(def_stmt)) == SSA_NAME.  The equality comparison afterwards is ok, as
SSA_NAMEs are unique and can be compared with pointer comparisons.

3)                 sqrt_recip_count ++;
formatting (no space in between variable name and ++).  Happens several times
in the function.

4) 
  /* Do the expensive part only if we can hope to optimize something.  */
  if (count + square_recip_count >= threshold
      && count >= 1)
This condition should have been on a single line, it is short enough to fit.