[PATCH] Fix an assert in legalization caused by 81f64c04

[escha]

> On May 29, 2015, at 11:05 AM, Matt Arsenault <arsenm2 at gmail.com> wrote:
> 
> 
>> On May 29, 2015, at 10:51 AM, escha <escha at apple.com <mailto:escha at apple.com>> wrote:
>> 
>> 
>>     /// Returns a type large enough to hold any valid shift amount - before type
>>     /// legalization these can be huge.
>>     EVT getShiftAmountTy(EVT LHSTy) {
>>       assert(LHSTy.isInteger() && "Shift amount is not an integer type!");
>>       if (LHSTy.isVector())
>>         return LHSTy;
>>       return LegalTypes ? TLI.getScalarShiftAmountTy(LHSTy)
>>                         : TLI.getPointerTy();
>>     }
>> 
> 
> I didn’t know about this one. Why does this exist? This seems insane. Does anything break if you replace everything with TLI.getShiftAmountTy()?

If I understand correctly, the reasoning is like this…

On x86:

    MVT getScalarShiftAmountTy(EVT LHSTy) const override { return MVT::i8; }

But prior to legalization you can have large types, e.g. i1024, whose shift amounts won’t fit in i8. So you need to allow larger shift types.

—escha
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