[all-commits] [llvm/llvm-project] 078198: [DebugInfo][InstrRef] Index DebugVariables and som...

[Jeremy Morse via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 078198f310d55925ccd9e1aa5b6ff4af3b36bbc7
      https://github.com/llvm/llvm-project/commit/078198f310d55925ccd9e1aa5b6ff4af3b36bbc7
  Author: Jeremy Morse <jeremy.morse at sony.com>
  Date:   2024-07-18 (Thu, 18 Jul 2024)

  Changed paths:
    M llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
    M llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h
    M llvm/test/DebugInfo/MIR/X86/live-debug-values-fragments.mir
    M llvm/unittests/CodeGen/InstrRefLDVTest.cpp

  Log Message:
  -----------
  [DebugInfo][InstrRef] Index DebugVariables and some DILocations (#99318)

A lot of time in LiveDebugValues is spent computing DenseMap keys for
DebugVariables, and they're made up of three pointers, so are large.
This patch installs an index for them: for the SSA and value-to-location
mapping parts of InstrRefBasedLDV we don't need to access things like
the variable declaration or the inlining site, so just use a uint32_t
identifier for each variable fragment that's tracked. The compile-time
performance improvements are substantial (almost 0.4% on the tracker).

About 80% of this patch is just replacing DebugVariable references with
DebugVariableIDs instead, however there are some larger consequences. We
spend lots of time fetching DILocations when emitting DBG_VALUE
instructions, so index those with the DebugVariables: this means all
DILocations on all new DBG_VALUE instructions will normalise to the
first-seen DILocation for the variable (which should be fine).

We also used to keep an ordering of when each variable was seen first in
a DBG_* instruction, in the AllVarsNumbering collection, so that we can
emit new DBG_* instructions in a stable order. We can hang this off the
DebugVariable index instead, so AllVarsNumbering is deleted.

Finally, rather than ordering by AllVarsNumbering just before DBG_*
instructions are linked into the output MIR, store instructions along
with their DebugVariableID, so that they can be sorted by that instead.



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