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switch to a new CFG selection logic #116

Merged
merged 2 commits into from
Sep 11, 2024
Merged

switch to a new CFG selection logic #116

merged 2 commits into from
Sep 11, 2024

Commits on Sep 10, 2024

  1. switch to a new CFG selection logic 

    This commit aims to port the new CFG selection logic implemented in
aviatesk/JET.jl#654 to LCU, so that it can be shared between LCU and JET.

The new algorithm is based on what was proposed in [Wei84][^Wei84]. If there is
even one active block in the blocks reachable from a conditional branch
up to its successors' nearest common post-dominator (referred to as
"𝑰𝑵𝑭𝑳" in the paper), it is necessary to follow that conditional
branch and execute the code. Otherwise, execution can be
short-circuited[^short-circuit] from the conditional branch to the
nearest common post-dominator.

Regarding the `GotoNode`, it is now marked only for active blocks after
all requirements have converged, rather than marking it inside the
`add_loop!` or such. This approach eliminates the need to add
unnecessary blocks inside the loop, and the need to use `add_loop!`
while allowing the required CFG to be executed safely.

[^Wei84]: M. Weiser, "Program Slicing," IEEE Transactions on Software Engineering, 10, pages 352-357, July 1984. https://ieeexplore.ieee.org/document/5010248

[^short-circuit]: It is important to note that in Julia's IR (`CodeInfo`),
  "short-circuiting" a specific code region is not a simple task. Simply
  ignoring the path to the post-dominator does not guarantee fall-through
  to the post-dominator. Therefore, a more careful implementation is
  required for this aspect.
    @aviatesk
    aviatesk committed Sep 10, 2024
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  2. remove add_loops!

    @aviatesk
    aviatesk committed Sep 10, 2024
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