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winch: Add support for br_table #6951

Merged
merged 4 commits into from
Sep 2, 2023
Merged

winch: Add support for br_table #6951

merged 4 commits into from
Sep 2, 2023

Commits on Sep 1, 2023

  1. winch: Add support for br_table 

    This change adds support for the `br_table` instruction, including
several modifications to the existing control flow implementation:

* Improved handling of jumps to loops: Previously, the compiler erroneously
treated the result of loop blocks as the definitive result of the jump. This
change fixes this bug.

* Streamlined result handling and stack pointer balancing: In the past, these
operations were executed in two distinct steps, complicating the process of
ensuring the correct invariants when emitting unconditional jumps. To simplify
this, `CodeGenContext::unconditional_jump` is introduced . This function
guarantees all necessary invariants are met, encapsulating the entire operation
within a single function for easier understanding and maintenance.

* Handling of unreachable state at the end of a function: when reaching the end
of a function in an unreachable state, clear the stack and ensure that the
machine stack pointer is correctly placed according to the expectations of the
outermost block.

In addition to the above refactoring, the main implementation of the
`br_table` instruction involves emitting labels for each target. Within each
label, an unconditional jump is emitted to the frame's label, ensuring correct
stack pointer balancing  when the jump is emitted.

While it is possible to optimize this process by avoiding intermediate labels
when balancing isn't required, I've opted to maintain the current
implementation until such optimization becomes necessary.
    @saulecabrera
    saulecabrera committed Sep 1, 2023
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  2. chore: Rust fmt

    @saulecabrera
    saulecabrera committed Sep 1, 2023
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  3. fuzzing: Add BrTable to list of support instructions

    @saulecabrera
    saulecabrera committed Sep 1, 2023
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  4. docs: Improve documentation for unconditional_jump

    @saulecabrera
    saulecabrera committed Sep 1, 2023
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