[PATCH, AARCH64] : Fix target/59744 - invalid use of CMN

Richard Earnshaw rearnsha@arm.com
Fri Jan 10 17:39:00 GMT 2014


On 10/01/14 17:37, Andrew Pinski wrote:
> On Fri, Jan 10, 2014 at 7:14 AM, Richard Earnshaw <rearnsha@arm.com> wrote:
>> It's incorrect to use CMN to compare with a negated operand if the
>> following condition is an inequality.  This is because of boundary
>> conditions when the negated operations overflow (or when zero), since
>> the flags are then not the swapped version of the comparison.
> 
> I think the functions in the testcase need noclone attribute also.
> 

Why?

R.

> Thanks,
> Andrew
> 
>>
>> This patch restricts the pattern to CC_Zmode (a new mode for the
>> comparison flags).
>>
>> gcc:
>>         PR target/59744
>>         * aarch64-modes.def (CC_Zmode): New flags mode.
>>         * aarch64.c (aarch64_select_cc_mode): Only allow NEG when the
>>         condition represents an equality.
>>         (aarch64_get_condition_code0): Handle CC_Zmode.
>>         * aarch64.md (compare_neg<mode>): Restrict to equality
>>         operations.
>>
>> testsuite:
>>         PR target/59744
>>         * gcc.target/aarch64/cmn-neg.c: Use equality comparisons.
>>         * gcc.target/aarch64/cmn-neg2.c: New test.
>>
>> Committed to trunk.
>>
>> R.
> 




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