[PATCH] D58386: [DebugInfo] Pre-RA MachineSink: sink DBG_VALUEs that don't immediately follow the sunk instruction too

[Jeremy Morse via Phabricator via llvm-commits]

jmorse created this revision.
jmorse added reviewers: aprantl, bjope, vsk.
Herald added subscribers: llvm-commits, jdoerfert.
Herald added a project: LLVM.
jmorse added a parent revision: D58238: [DebugInfo] MachineSink: Insert undef DBG_VALUEs when sinking instructions, try to forward copies.

This patch improves the pre-register-allocation portions of MachineSink. Two things happen here -- firstly we collect DBG_VALUEs seen when walking through a machine basic block and record their virtual-register uses, so that it's easy to determine what debuginfo to sink when an instruction sinks. This avoids relying on the unsound collectDebugValues function, and so will collect DBG_VALUEs that don't immediately follow the sunk instruction.

Secondly, debug users of what an instruction defines may no longer be dominated after that instruction sinks (see: the added test case). It's possible to salvage some of these debug users if the sunk instruction was a copy (which can be propagated), and I've added a function to do this.

On a clang-3.4 build we save a fractional number of variable locations and increase covered scope-bytes by ~0.5%.

The copy-propagation to no-longer-dominated instructions makes zero contribution to that coverage improvement -- it's there mostly to ease some test failures that occur when CodeGenPrepare::placeDbgValues is deleted, a patch I will totally upload this week. If the copy-prop part of this patch is dubious, I can fold it into that later patch, where it's easier to see what's going on.


Repository:
  rL LLVM

https://reviews.llvm.org/D58386

Files:
  lib/CodeGen/MachineSink.cpp
  test/DebugInfo/MIR/X86/machinesink.mir

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D58386.187361.patch
Type: text/x-patch
Size: 11624 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190219/1e0ec3c3/attachment.bin>