[PING] Keep TBAA info when rewriting load and store DAG nodes

[Richard Sandiford]

Chris Lattner <clattner at apple.com> writes:
> LGTM!  Thanks Richard,

r193517, thanks.

> -Chris
>
> On Oct 16, 2013, at 3:05 AM, Richard Sandiford
> <rsandifo at linux.vnet.ibm.com> wrote:
>
>> Second ping.  Please let me know if there's something I can do to make
>> this easier to review.
>> 
>> Richard Sandiford <rsandifo at linux.vnet.ibm.com> writes:
>>> Most SelectionDAG code drops the TBAA info when creating a new form of a
>>> load and store (e.g. during legalisation, or when converting a plain
>>> load to an extending one).  This patch tries to catch all cases where
>>> the TBAA information can legitimately be carried over.
>>> 
>>> There is nice getTruncStore() function that allows the original
>>> MachineMemOperand to be passed instead of the individual fields.  The
>>> patch adds a similar thing for getLoad() and getExtLoad().
>>> 
>>> The idea is to use the MachineMemOperand forms when all fields are
>>> carried over (size, pointer info, isVolatile, isNonTemporal, alignment
>>> and TBAA info).  If some adjustment is being made, e.g. to narrow the
>>> load, then we still pass the individual fields but also pass the TBAA
>>> info.
>>> 
>>> This is trying to update all uses in SelectionDAG/, so I don't have a
>>> testcase for all of them.  But the patch includes an example where the
>>> change helps for SystemZ.  (I'm hoping to make useAA() the default for
>>> SystemZ if this goes in, but that's a separate change.  I'll drop the
>>> explicit -combiner-* flags when that happens.)
>>> 
>>> 
>>> http://llvm-reviews.chandlerc.com/D1894
>>> 
>>> Files:
>>>  include/llvm/CodeGen/SelectionDAG.h
>>>  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>>>  lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
>>>  lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp
>>>  lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
>>>  lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
>>>  lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
>>>  lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
>>>  lib/CodeGen/SelectionDAG/SelectionDAG.cpp
>>>  test/CodeGen/SystemZ/alias-01.ll
>> 
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