[Bug rtl-optimization/17935] Two consecutive movzbl are generated

[kazu at cs dot umass dot edu]

------- Additional Comments From kazu at cs dot umass dot edu  2004-12-12 17:57 
-------
With today's mainline, I get

bar:
        movl    4(%esp), %eax
        testb   $1, (%eax)
        jne     .L2
        movl    8(%esp), %eax
        testb   $1, (%eax)
        jne     .L2
        movl    $1, %eax
        movzbl  %al, %eax
        ret
        .p2align 2,,3
.L2:
        xorl    %eax, %eax
        movzbl  %al, %eax
        ret

Still we have a similar problem.  movl (or xorl) followed by movzbl is
meaningless.

It turns out that the fix for PR 14843 can fix this at tree level.
Here is the resulting assembly with my patch for PR 14843.

bar:
        movl    4(%esp), %eax
        testb   $1, (%eax)
        jne     .L2
        movl    8(%esp), %eax
        testb   $1, (%eax)
        jne     .L2
        movl    $1, %eax
        ret
        .p2align 2,,3
.L2:
        xorl    %eax, %eax
        ret

The reason my patch fixes this is because it removes casts before expansion.

Without my patch:

bar (p, q)
{
  int iftmp.0;

<bb 0>:
  if (p->f0 != 0) goto <L3>; else goto <L0>;

<L0>:;
  if (q->f0 != 0) goto <L3>; else goto <L7>;

<L7>:;
  iftmp.0 = 1;
  goto <bb 4> (<L8>);

<L3>:;
  iftmp.0 = 0;

<L8>:;
  return (int) (_Bool) iftmp.0;  <-- Notice these casts

}

With my patch:

bar (p, q)
{
  int D.1122;

<bb 0>:
  if (p->f0 != 0) goto <L3>; else goto <L0>;

<L0>:;
  if (q->f0 != 0) goto <L3>; else goto <L7>;

<L7>:;
  D.1122 = 1;
  goto <bb 4> (<L8>);

<L3>:;
  D.1122 = 0;

<L8>:;
  return D.1122;  <-- Casts are gone!

}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17935