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Handle embedded assignments in copy propagation #63447

Merged
merged 4 commits into from
Jan 21, 2022
Merged

Handle embedded assignments in copy propagation #63447

merged 4 commits into from
Jan 21, 2022

Commits on Jan 13, 2022

  1. Clean things up a little 

    Delete redundant conditions, use "LclVarDsc*", rename locals for clarity.
    @SingleAccretion
    SingleAccretion committed Jan 13, 2022
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  2. Delete a redundant condition 

    For actual def nodes, GTF_VAR_CAST will never be set, it is
only set in "optNarrowTree" for uses.

For "def nodes" that are actually uses (parameters), the VNs
will never match anyway.
    @SingleAccretion
    SingleAccretion committed Jan 13, 2022
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  3. Handle embedded assignments in copy propagation 

    Previously, as the comments in copy propagation tell us, it
did not handle "intervening", or not-top-level definitions of
locals, instead opting to maintain a dedicated kill set of them.

This is obviously a CQ problem, but also a TP one, as it meant
there had to be a second pass over the statement's IR, where
the definitions would be pushed on the stack.

This change does away with that, instead pushing new definitions
as they are encountered in execution order, and simultaneously
propagating on uses. Notably, this means the code now needs to
look at the real definition nodes, i. e. ASGs, not the LHS locals,
as those are encountered first in canonical execution order, i. e.
for a tree like:

```
  ASG
    LCL_VAR V00 "def"
    ADD
      LCL_VAR V00
      LCL_VAR V00
```

Were we to use the "def" as the definition point, we would wrongly
push it as the definition on the stack, even as the assignments
itself hasn't happened yet at that point.

There are nice diffs with this change, all resulting from unblocked
propagations, and mostly coming from setup arguments under calls.
    @SingleAccretion
    SingleAccretion committed Jan 13, 2022
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  4. Simplify optIsSsaLocal

    @SingleAccretion
    SingleAccretion committed Jan 13, 2022
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