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JIT: Enable edge based profiles for all scenarios #80481

Merged
merged 2 commits into from
Jan 13, 2023
Merged

JIT: Enable edge based profiles for all scenarios #80481

merged 2 commits into from
Jan 13, 2023

Commits on Jan 11, 2023

  1. JIT: Enable edge based profiles for all scenarios 

    Enable edge based profiles for OSR, partial compilation, and optimized plus
instrumented cases.

For OSR this requires deferring flow graph modifications until after we have
built the initial probe list, so that the initial list reflects the entirety
of the method. This set of candidate edge probes is thus the same no matter how
the method is compiled. A given compile may schematize a subset of these probes
and materialize a subset of what gets schematized; this is tolerated by the PGO
mechanism provided that the initial instrumented jitting produces a schema which
is a superset of the schema produced by any subsequent instrumented rejitting.
This is normally the case.

Partial compilation may still need some work to ensure full schematization but
it is currently off by default. Will address this subsequently.

For optimized compiles we give the EfficientEdgeCountInstrumentor the same kind
of probe relocation abilities that we have in the BlockCountInstrumentor. In
particular we need to move probes that might appear in return blocks that follow
implicit tail call blocks, since those return blocks must remain empty.

The details on how we do this are a bit different but the idea is the same: we
create duplicate copies of any probe that was going to appear in the return block
and instead instrument each pred. If the pred reached the return via a critical
edge, we split the edge and put the probe there. This analysis relies on cheap
preds, so to ensure we can use them we move all the critial edge splitting so it
happens before we need the cheap pred lists.

The ability to do block profiling is retained but will no longer be used without
special config settings.

There were also a few bug fixes in the spanning tree visitor. It must visit a
superset of the blocks we end up importing and was missing visits in some cases.

This should improve jit time and code quality for instrumented code.

Fixes dotnet#47942.
Fixes dotnet#66101.
Contributes to dotnet#74873.
    @AndyAyersMS
    AndyAyersMS committed Jan 11, 2023
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  2. handle splitting when importer has optimized the branch

    @AndyAyersMS
    AndyAyersMS committed Jan 11, 2023
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