[Bug rtl-optimization/22568] Should use cmov in some stituations

[rguenth at gcc dot gnu dot org]

------- Additional Comments From rguenth at gcc dot gnu dot org  2005-09-02 
09:54 -------
Blindly applying ifcvt to something like

int a,b;
void foo(int flag)
{
  int x;
  if (flag)
    x=a,a=b,b=x;
}

because we're presented with

  if (flag)
  {
    int reg_a = a;
    x = reg_a;
    int reg_b = b;
    a = reg_b;
    b = x;
  }

and we get cmovs for loading a,b into pseudos instead of
loading them unconditionally.  F.i.

int a,b;
void foobar(int flag)
{
  if (flag)
    a = b;
}

will become

foobar:
        movl    4(%esp), %eax   # flag, flag
        testl   %eax, %eax      # flag
        cmovne  b, %edx # b,, b
        movl    a, %eax # a, tmp61
        cmovne  %edx, %eax      # b,, tmp61
        movl    %eax, a # tmp61, a
        ret

notice how we special-cased the _store_ to use a temporary.  I'll
try applying the same for loads.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22568