#120613 removed -ubsan-unique-traps and replaced it with
-fno-sanitize-merge (introduced in #120511), which allows fine-grained
control of which UBSan checks to prevent merging. This analogous patch
removes -bound-checking-unique-traps, and allows it to be controlled via
-fno-sanitize-merge=local-bounds.
Most of this patch is simply plumbing through the compiler flags into
the bounds checking pass.
Note: this patch subtly changes -fsanitize-merge (the default) to also
include -fsanitize-merge=local-bounds. This is different from the
previous behavior, where -fsanitize-merge (or the old
-ubsan-unique-traps) did not affect local-bounds (requiring the separate
-bounds-checking-unique-traps). However, we argue that the new behavior
is more intuitive.
Removing -bounds-checking-unique-traps and merging its functionality
into -fsanitize-merge breaks backwards compatibility; we hope that this
is acceptable since '-mllvm -bounds-checking-unique-traps' was an
experimental flag.
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