llvm dev - Dec 2012 - [LLVMdev] [RFC] Replacing EVT:s with MVT:s (when possible)

There seems to be quite a few places where the EVT type is used, but the code
asserts if the variable/parameter is assigned something else than an MVT. Are
there any general objections to replace EVT with MVT in these cases?

For example, a quick look at TargetLowering.h give me this list of (member)
functions, taking an EVT parameter, that asserts if the argument is not an MVT:

getRegClassFor, getRepRegClassFor, getRepRegClassCostFor, setTypeAction,
getLoadExtAction, isLoadExtLegal, getTruncStoreAction, isTruncStoreLegal,
getIndexedLoadAction, getIndexedStoreAction, getCondCodeAction,
getTypeToPromoteTo, addRegisterClass

Regards,
Patrik Hägglund
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On Dec 3, 2012, at 1:14 PM, Patrik Hägglund H <patrik.h.hagglund at
ericsson.com> wrote:
> There seems to be quite a few places where the EVT type is used, but the
code asserts if the variable/parameter is assigned something else than an MVT.
Are there any general objections to replace EVT with MVT in these cases?
>  
> For example, a quick look at TargetLowering.h give me this list of (member)
functions, taking an EVT parameter, that asserts if the argument is not an MVT:
>  
> getRegClassFor, getRepRegClassFor, getRepRegClassCostFor, setTypeAction,
getLoadExtAction, isLoadExtLegal, getTruncStoreAction, isTruncStoreLegal,
getIndexedLoadAction, getIndexedStoreAction, getCondCodeAction,
getTypeToPromoteTo, addRegisterClass
>  
Please do.  MVT is cheaper than EVT and conceptually cleaner when dealing with
physical machine types.  EVT should only be used in parts of the code generator
that are "pre-legalization" because they can represent arbitrary IR
types.  Anything that takes a legal machine type should take an MVT.

-Chris

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On 3 Dec 2012, at 23:45, Chris Lattner wrote:
> Please do.  MVT is cheaper than EVT and conceptually cleaner when dealing
with physical machine types.  EVT should only be used in parts of the code
generator that are "pre-legalization" because they can represent
arbitrary IR types.  Anything that takes a legal machine type should take an
MVT.
A side issue of this is that it is currently relatively hard to add new
machine-specific register types.  The only way of doing this involves extending
MVT, which requires tweaking three files in the (nominally) target-independent
parts of the compiler.  It would be great if we could simply reserve a (small?)
number of MVTs for target-specific legal values.

David