[PATCH][TargetInstrInfo] Fix the implementation of commuteInstruction to match the comment of the API

[Quentin Colombet]

Thanks Tom!

This is r208371.

-Quentin

On May 8, 2014, at 4:13 PM, Tom Stellard <tom at stellard.net> wrote:

> LGTM.
> 
> -Tom
> 
> On Thu, May 08, 2014 at 04:04:13PM -0700, Quentin Colombet wrote:
>> Hi,
>> 
>> The proposed patch relaxes the behavior of TargetInstrInfo::commuteInstruction when TargetInstrInfo::findCommutedOpIndices returns false.
>> 
>> Currently TargetInstrInfo triggers a fatal error in such situation whereas based on the comment in the API[1] it should just return nullptr. Indeed the only precondition that should be ensured is that the instruction must be commutable.
>> 
>> Spotted via code inspection.
>> 
>> Is it okay to commit?
>> 
>> [1]
>>  /// commuteInstruction - If a target has any instructions that are
>>  /// commutable but require converting to different instructions or making
>>  /// non-trivial changes to commute them, this method can overloaded to do
>>  /// that.  The default implementation simply swaps the commutable operands.
>>  /// If NewMI is false, MI is modified in place and returned; otherwise, a
>>  /// new machine instruction is created and returned.  Do not call this
>>  /// method for a non-commutable instruction, but there may be some cases
>>  /// where this method fails and returns null.
>> 
>> Thanks,
>> -Quentin
> 
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> 

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