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Support Arm64 "constructed" constants in SuperPMI asm diffs #76616

Merged
merged 3 commits into from
Oct 5, 2022
Merged

Support Arm64 "constructed" constants in SuperPMI asm diffs #76616

merged 3 commits into from
Oct 5, 2022

Commits on Oct 4, 2022

  1. Support Arm64 "constructed" constants in SuperPMI asm diffs 

    SuperPMI asm diffs tries to ignore constants that can change between
multiple replays, such as addresses that the replay engine must generate
and not simply hand back from the collected data.

Often, addresses have associated relocations generated during replay.
SuperPMI can use these relocations to adjust the constants to allow
two replays to match. However, there are cases on Arm64 where an address
both doesn't report a relocation and is "constructed" using multiple
`mov`/`movk` instructions.

One case is the `allocPgoInstrumentationBySchema()`
API which returns a pointer to a PGO data buffer. An address within this
buffer is constructed via a sequence such as:
```
mov     x0, dotnet#63408
movk    x0, dotnet#23602, lsl dotnet#16
movk    x0, dotnet#606, lsl dotnet#32
```

When SuperPMI replays this API, it constructs a new buffer and returns that
pointer, which is used to construct various actual addresses that are
generated as "constructed" constants, shown above.

This change "de-constructs" the constants and looks them up in the replay
address map. If base and diff match the mapped constants, there is no asm diff.
    @BruceForstall
    BruceForstall committed Oct 4, 2022
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  2. Fix 32-bit build 

    I don't think we fully support 64-bit replay on 32-bit host, but this
fix at least makes it possible for this case.
    @BruceForstall
    BruceForstall committed Oct 4, 2022
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  3. Support more general mov/movk sequence 

    Allow JIT1 and JIT2 to have a different sequence of
mov/movk[/movk[/movk]] that map to the same address in the
address map. That is, the replay constant might require a different
set of instructions (e.g., if a `movk` is missing because its constant
is zero).
    @BruceForstall
    BruceForstall committed Oct 4, 2022
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