Fix bounds-check elision with 4 GiB guard pages. #11973
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First, this fixes the `can_elide_bounds_check` function to consider the guard size when determining whether all 32 bits of a 32-bit index space will be at least reserved. This allows configurations which use 4 GiB guard regions with smaller memory reservations to benefit from bounds check eliding. Second, this fixes a subtract overflow in `bounds_check_field_access` when the offset is greater than the memory reservation size. In this case, optimization isn't important because the code can only ever trap, so the change here is just to avoid panicking in the compiler.
sunfishcode
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alexcrichton
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alexcrichton
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Nov 4, 2025
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This patch exposed winch to more bounds-check-elision cases than it had been exposed to before, so I had to make some more substantial winch changes. |
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alexcrichton
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Nov 4, 2025
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First, this fixes the
can_elide_bounds_checkfunction to consider the guard size when determining whether all 32 bits of a 32-bit index space will be at least reserved. This allows configurations which use 4 GiB guard regions with smaller memory reservations to benefit from bounds check eliding.Second, this fixes a subtract overflow in
bounds_check_field_accesswhen the offset is greater than the memory reservation size. In this case, optimization isn't important because the code can only ever trap, so the change here is just to avoid panicking in the compiler.