[PATCH] CodeGenPrepare: Avoid and/or i1 in select conditions.

[Ahmed Bougacha]

On Fri, Feb 6, 2015 at 11:43 AM, hfinkel at anl.gov <hfinkel at anl.gov> wrote:
> In http://reviews.llvm.org/D7399#119931, @MatzeB wrote:
>
>> On a side note: Ahmed just mentioned a snipped from SelectionDAGBuilder to me that has pretty much the same logic I do for selects implemented for branches:
>>
>>   // If this is a series of conditions that are or'd or and'd together, emit
>>    // this as a sequence of branches instead of setcc's with and/or operations.
>>    // As long as jumps are not expensive, this should improve performance.
>>    // For example, instead of something like:
>>    //     cmp A, B
>>    //     C = seteq
>>    //     cmp D, E
>>    //     F = setle
>>    //     or C, F
>>    //     jnz foo
>>    // Emit:
>>    //     cmp A, B
>>    //     je foo
>>    //     cmp D, E
>>    //     jle foo
>>    //
>>
>> ...
>>
>> no idea why that is in SelectionDAGBuilder, it also doesn't seem strictly beneficial to all targets to me...
>
>
> It's not (and it was pointed out to me in a different thread a couple of months ago); which function does this again? I keep forgetting to fix this... (my current plan is to turn it off when TLI->hasMultipleConditionRegisters() is true, which is only the case on PPC AFAIK).

It's in SelectionDAGBuilder::visitBr.

-Ahmed

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