Of the 128-bits of buffer descriptor only 48 bits are address bits, so
following the discussion on https://discourse.llvm.org/t/clarifiying-the-semantics-of-ptrtoint/83987/54,
the logic conclusion is to set the index width to 48 bits instead of
the current value of 128.

Most of the test changes are mechanical datalayout updates, but there
is one actual change: the ptrmask test now uses .i48 instead of .i128
and I had to update SelectionDAGBuilder to correctly extend the mask.

Reviewed By: krzysz00

Pull Request: https://github.com/llvm/llvm-project/pull/139419

Reapply  #135326 and fix the target-dependent constant check.

---------

Co-authored-by: Matt Arsenault <arsenm2@gmail.com>

This reverts commit 76ced7fa782f0d7db9efea871fa6de74706dd9cc since it breaks a
lot of bots.

insert `readfirstlane` in the function returns in sgpr.

The ptrmask intrinsic requires the integer mask to be the index size,
not the pointer size.

Currently, we specify that the ptrmask intrinsic allows the mask to have
any size, which will be zero-extended or truncated to the pointer size.

However, what semantics of the specified GEP expansion actually imply is
that the mask is only meaningful up to the pointer type *index* size --
any higher bits of the pointer will always be preserved. In other words,
the mask gets 1-extended from the index size to the pointer size. This
is also the behavior we want for CHERI architectures.

This PR makes two changes:
* It spells out the interaction with the pointer type index size more
explicitly.
* It requires that the mask matches the pointer type index size. The
intention here is to make handling of this intrinsic more robust, to
avoid accidental mix-ups of pointer size and index size in code
generating this intrinsic. If a zero-extend or truncate of the mask is
desired, it should just be done explicitly in IR. This also cuts down on
the amount of testing we have to do, and things transforms needs to
check for.

As far as I can tell, we don't actually support pointers with different
index type size at the SDAG level, so I'm just asserting the sizes match
there for now. Out-of-tree targets using different index sizes may need
to adjust that code.

SIInsertWaitcnts inserts waitcnt instructions to resolve data
dependencies. The GFX10+ vscnt (VMEM store count) counter is never used
in this way. It is only used to resolve memory dependencies, and that is
handled by SIMemoryLegalizer. Hence there is no need to conservatively
wait for vscnt to be 0 on function entry and before returns.

Differential Revision: https://reviews.llvm.org/D153537

Add GFX11 test coverage to a bunch of tests where it was easy to do so,
mostly because the checks are autogenerated and/or GFX11 can share the
same checks as GFX10.

Differential Revision: https://reviews.llvm.org/D129295

Differential Revision: https://reviews.llvm.org/D99267