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Re: Fix PR 19643. [ Was Re: Speedup CSE by 5% ]

Hi Jeff,

On Fri, 28 Jan 2005, Jeffrey A Law wrote:
> On Thu, 2005-01-27 at 18:33 -0500, Kazu Hirata wrote:
> > In case you wonder where three occurrences in the MINUS case come
> > from, I've filed a PR 19643.
> This fixes PR 19643 in the obvious way.

Alas, not so "obvious" as this is clearly incorrect.

>!       /* 0 % X is always zero as is X % 1.  */
>!       if (integer_zerop (arg0) || integer_onep (arg1))
>          return omit_one_operand (type, integer_zero_node, arg0);

If the first argument is integer_zerop, then its the second operand
arg1 that needs to be evaluated for potential side-effects before
returning zero.

i.e. something closer might be

        if (integer_onep (arg1))
          return omit_one_operand (type, integer_zero_node, arg0);
	if (integer_zerop (arg0))
	  return omit_one_operand (type, integer_zero_node, arg1);

We should add a "0 % x++" testcase to the testsuite (if there isn't
one already).  p.s. don't forget to list the target-triple that you
bootstrap and regression test on when you post a correction.

I'm still investigating possible java front-end interactions and
whether gcj/bytecode requires the evaluation of "0 % 0" to throw
a java.lang.ArithmeticException.


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