Using options like -filetype=null instead should allow tools to save
some work by not generating any output.

They had it before but that was removed in #150024. They need to disable the check explicitly to pass expensive checks.

Recent upstream trends have moved away from explicitly using `-verify-machineinstrs`, as it's already covered by the expensive checks. This PR removes almost all `-verify-machineinstrs` from tests in `llvm/test/CodeGen/AMDGPU/*.ll`, leaving only those tests where its removal currently causes failures.

In gfx90a-gfx950, it's possible to emit MFMAs which use AGPRs or VGPRs
for vdst and src2. We do not want to do use the AGPR form, unless
required by register pressure as it requires cross bank register
copies from most other instructions. Currently we select the AGPR
or VGPR version depending on a crude heuristic for whether it's possible
AGPRs will be required. We really need the register allocation to
be complete to make a good decision, which is what this pass is for.
    
This adds the pass, but does not yet remove the selection patterns
for AGPRs. This is a WIP, and NFC-ish. It should be a no-op on any
currently selected code. It also does not yet trigger on the real
examples of interest, which require handling batches of MFMAs at
once.

Causes bot failure: https://lab.llvm.org/buildbot/#/builders/55/builds/4246/steps/11/logs/stdio

This reverts commit 7a648554f886fbc043c4f3f58ca88f6c4535f2cf.

No need to generate a stack trace and a GitHub issue prompt on a wrongly
set regalloc option.

This reverts commit c2fc7f75f67039bb1ed577bc0edbd699a850cd9d. As the
dependent patch about split vgpr regalloc pipeline solved the issue(#96353).

Allocating wwm-registers and per-thread VGPR operands
together imposes many challenges in the way the
registers are reused during allocation. There are
times when regalloc reuses the registers of regular
VGPRs operations for wwm-operations in a small range
leading to unwantedly clobbering their inactive lanes
causing correctness issues that are hard to trace.

This patch splits the VGPR allocation pipeline further
to allocate wwm-registers first and the regular VGPR
operands in a separate pipeline. The splitting would
ensure that the physical registers used for wwm
allocations won't take part in the next allocation
pipeline to avoid any such clobbering.

This reverts commit 4b9112e88a998ce620e4683548f2afd17cc5fe95. A separate
issue(#96353) describing it has been opened to further keep its track.