Zero alloc: move checkmach pass before Comballoc and CSE #1786
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These passes do not change allocations but manipulate debuginfo. Checking before it does not need to adjust these passes for Debuginfo.assume_zero_alloc. This should be reconsidered if add other properties to check, but so far the properties we have considered can be checked before comballoc (no indirect calls, no raise, no updates for dynamic memory).
xclerc
approved these changes
Aug 30, 2023
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As discussed in #1762, CSE and Comballoc interferes with zero_alloc check. Instead of fixing the backend CSE pass to correctly propagate debuginfo with
assume_zero_alloc, this PR movescheckmachpass earlier. This is fine because CSE and Comballoc preserve "zero_alloc" property at function level. This may not remain true if we add other properties in the future, but it is true for all other properties we have considered so far (no indirect calls, no raise, is pure).