This only changes the types around. It doesn't rewrite existing uses
to std::optional, which we can do incrementally.
absl::optional to std::optional seems to have two visible impacts.
First, the field order is different (bool first vs bool last).
std::optional's order (bool last) seems to be better overall, decreasing
binary size. Second, absl::optional's assertions crash with
__builtin_trap, while std::optional calls __libcpp_verbose_abort which
calls base::ImmediateCrash. __builtin_trap permits the compiler to
combine crash sites within a function but leads to worse crash
debugging. In base::ImmediateCrash, we'd made a conscious decision to
prefer debuggability and pay some binary size for it. The net size
increase brings our optional type in line with that preference.
For more details see the discussion and document below:
https://groups.google.com/a/chromium.org/g/cxx/c/XG3G85_ZF1k/m/_QN8adIJBQAJhttps://docs.google.com/document/d/1AW7q9HCLOk738OCj8Z2U_AKVUC0YIFZWuyRvv09XTHk/edit
Binary-Size: See discussion above.
Fuchsia-Binary-Size: See discussion above.
Bug: 1373619
Change-Id: I85ca2b5dc3929852cdca8a915ebadb26d557af45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4469528
Commit-Queue: David Benjamin <davidben@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1204351}
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