[all-commits] [llvm/llvm-project] 14aaaa: Re-apply 3fab2d138e30, now with a triple added

[Jeremy Morse via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 14aaaa12366f7d1328b5ec81c71c63de9d878e75
      https://github.com/llvm/llvm-project/commit/14aaaa12366f7d1328b5ec81c71c63de9d878e75
  Author: Jeremy Morse <jeremy.morse at sony.com>
  Date:   2022-02-02 (Wed, 02 Feb 2022)

  Changed paths:
    M llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
    M llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h
    A llvm/test/DebugInfo/MIR/InstrRef/spill-slot-limits.mir
    M llvm/unittests/CodeGen/InstrRefLDVTest.cpp

  Log Message:
  -----------
  Re-apply 3fab2d138e30, now with a triple  added

Was reverted in 1c1b670a73a9 as it broke all non-x86 bots. Original commit
message:

[DebugInfo][InstrRef] Add a max-stack-slots-to-track cut-out

In certain circumstances with things like autogenerated code and asan, you
can end up with thousands of Values live at the same time, causing a large
working set and a lot of information spilled to the stack. Unfortunately
InstrRefBasedLDV doesn't cope well with this and consumes a lot of memory
when there are many many stack slots. See the reproducer in D116821.

It seems very unlikely that a developer would be able to reason about
hundreds of live named local variables at the same time, so a huge working
set and many stack slots is an indicator that we're likely analysing
autogenerated or instrumented code. In those cases: gracefully degrade by
setting an upper bound on the amount of stack slots to track. This limits
peak memory consumption, at the cost of dropping some variable locations,
but in a rare scenario where it's unlikely someone is actually going to
use them.

In terms of the patch, this adds a cl::opt for max number of stack slots to
track, and has the stack-slot-numbering code optionally return None. That
then filters through a number of code paths, which can then chose to not
track a spill / restore if it touches an untracked spill slot. The added
test checks that we drop variable locations that are on the stack, if we
set the limit to zero.

Differential Revision: https://reviews.llvm.org/D118601