[Bug tree-optimization/31849] [4.3 Regression] Code size regression caused by fix to PR 31360

[ebotcazou at gcc dot gnu dot org]

------- Comment #19 from ebotcazou at gcc dot gnu dot org  2007-11-24 18:43 
-------
The pessizimation actually happens at the tree level, -fivopts turns

<bb 9>:
  s1 = (long unsigned int) *buf + s1;
  buf = buf + 1;
  s2 = s1 + s2;
  k = k + -1;
  if (k != 0)
    goto <bb 9>;
  else
    goto <bb 10>;

into

<bb 10>:
  s1 = s1 + (long unsigned int) MEM[base: buf.91, index: D.1322];
  s2 = s1 + s2;
  D.1322 = D.1322 + 1;
  if (D.1322 != (unsigned int) k)
    goto <bb 10>;
  else
    goto <bb 11>;

in final_cleanup.


Couldn't ivopts be taught to recognize "dec and branch on zero" patterns

  k_114 = k_15 + -1;
  if (k_114 != 0)
    goto <bb 10>;
  else
    goto <bb 11>;

and take into account their breakage for its cost estimates somehow?


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu dot
                   |                            |org
          Component|rtl-optimization            |tree-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31849