[all-commits] [llvm/llvm-project] d4c667: Avoid unnecessary uses of `MDNode::getTemporary`, NFC

[Duncan P. N. Exon Smith via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: d4c667c9af0335ac20015decce204c43f03a6cee
      https://github.com/llvm/llvm-project/commit/d4c667c9af0335ac20015decce204c43f03a6cee
  Author: Duncan P. N. Exon Smith <dexonsmith at apple.com>
  Date:   2020-10-26 (Mon, 26 Oct 2020)

  Changed paths:
    M clang/lib/CodeGen/CGLoopInfo.cpp
    M llvm/lib/Analysis/LoopInfo.cpp
    M llvm/lib/IR/MDBuilder.cpp
    M polly/lib/CodeGen/IRBuilder.cpp

  Log Message:
  -----------
  Avoid unnecessary uses of `MDNode::getTemporary`, NFC

This is a long-delayed follow-up to
5e5b85098dbeaea2cfa5d01695b5d2982634d7dd.

`TempMDNode` includes a bunch of machinery for RAUW, and should only be
used when necessary. RAUW wasn't being used in any of these cases... it
was just a placeholder for a self-reference.

Where the real node was using `MDNode::getDistinct`, just replace the
temporary argument with `nullptr`.

Where the real node was using `MDNode::get`, the `replaceOperandWith`
call was "promoting" the node to a distinct one implicitly due to
self-reference detection in `MDNode::handleChangedOperand`. The
`TempMDNode` was serving a purpose by delaying uniquing, but it's way
simpler to just call `MDNode::getDistinct` in the first place.

Note that using a self-reference at all in these places is a hold-over
from before `distinct` metadata existed. It was an old trick to create
distinct nodes. It would be intrusive to change, including bitcode
upgrades, etc., and it's harmless so I'm not sure there's much value in
removing it from existing schemas. After this commit it still has a tiny
memory cost (in the extra metadata operand) but no more overhead in
construction.

Differential Revision: https://reviews.llvm.org/D90079