[llvm] r188362 - Replace EVT with MVT in isVectorShift. Keeps compiler from generating unneeded checks and handling for extended types.

[Sean Silva]

Thanks for the info.

-- Sean Silva


On Wed, Aug 14, 2013 at 6:47 PM, Craig Topper <craig.topper at gmail.com>wrote:

> I believe every legal type for all supported targets needs to be
> represented in the enum inside of MVT. EVT is a wrapper around an MVT and a
> Type*. If the type is one of the MVT types the Type* is null and the MVT
> defines the define. Otherwise the MVT is INVALID_SIMPLE_VALUE_TYPE and the
> Type* points to a Type object that can represent an arbitrary type.
>
> SDNodes always use the EVT object to represent their types. But after
> types have been legalized all those EVTs should have an MVT value and null
> Type*.
>
> All of the places I converted from EVT to MVT were in operation
> legalization which occurs after type legalization. So everything should be
> an MVT at that point.
>
> During instruction selection SDNodes get turned into MachineSDNodes which
> still contain EVTs(which are really just MVTs). Then MachineSDNodes are
> converted to MachineInstructions. I believe that's the point when EVTs go
> away.
>
>
>
> On Wed, Aug 14, 2013 at 4:13 PM, Sean Silva <silvas at purdue.edu> wrote:
>
>> Hi Craig, do you know if we have any documentation regarding what MVT and
>> EVT are and how they fit in with the rest of the backend process? The
>> documentation for the respective classes in ValueTypes.h sheds some light
>> on the situation (MVT represents machine types, and EVT is a superset
>> including non-legal types), but it's not clear for example at what stage in
>> the codegen process they are formed and during which parts of the codegen
>> process they are relevant (e.g., they don't appear to be present at the MI
>> level (grepping MachineFunction.h and MachineInstr.h doesn't find
>> anything), so when do they go away?).
>>
>> -- Sean Silva
>>
>
>
>
> --
> ~Craig
>
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