[PATCH] D94264: [GlobalISel] Add MachineInstNumbering to CSEInfo and propagate CSE throughout AArch64 pipeline.

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

In D94264#2579990 <https://reviews.llvm.org/D94264#2579990>, @aemerson wrote:

> In D94264#2579954 <https://reviews.llvm.org/D94264#2579954>, @arsenm wrote:
>
>> I think legalizing/combining will do way, way more insertions than would happen in regalloc. Is this losing time to renumberings?
>
> On average, this does cost more in renumbering/flushing than it saves. It only provides a net benefit on the pathological cases in legalization & localization.
>
> In D94264#2579954 <https://reviews.llvm.org/D94264#2579954>, @arsenm wrote:
>
>> Would it make sense to increase the increment size?
>
> What do you mean by increment size?

The instruction index values initially increment by 16 so you only renumber for every 15 or so insertions between instructions:

  enum {
    /// The default distance between instructions as returned by distance().
    /// This may vary as instructions are inserted and removed.
    InstrDist = 4 * Slot_Count
  };


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