[PATCH] Special case clzl like builtins in factor_out_conditional_conversion (PR tree-optimization/71016)

[Jakub Jelinek]

On Wed, Jan 04, 2017 at 11:19:46AM +0100, Richard Biener wrote:
> For the SSA_NAME + INTEGER_CST case restrict it to the case
> 
>   if (x_1 > 5)
>     tem_2 = (char) x_1;
>   # tem_3 = PHI <tem_2, 5>
> 
> that is, (char) x_1 uses x_1 and that also appears in the controlling
> GIMPLE_COND.  That's what enables followup minmax replacement
> (gcc.dg/tree-ssa/pr66726.c).  Another case where it might be
> profitable is if the BB is empty after the conversion is sunk
> (may enable other value-replacement cases).

Do we actually have any testcases where we need the SSA_NAME + INTEGER_CST
case?
The only testcase that has been added that actually relied on the
factor_out_* is since r242750 handled during gimple folding (already in
*.gimple dump).

If I modify the testcase so that it isn't recognized by the minmax folding,
extern unsigned short y[];

int
foo (int x)
{
  return 64 < y[x] ? 68 : y[x];
}

then vanilla gcc vs. gcc with factor_out* INTEGER_CST case removed gives:
-	cmpw	$65, %ax
-	cmovnb	%edx, %eax
+	cmpw	$64, %ax
+	cmova	%edx, %eax
so not worse or better.  And, even when the conversion is the only stmt
in the basic block, that still doesn't allow the bb to be removed, we need
the empty bb for the PHIs.

	Jakub