[PATCH] D137707: Move "auto-init" instructions to the dominator of their users
Eli Friedman via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Nov 29 11:01:57 PST 2022
efriedma added a comment.
> we move the memory initialization marked as "auto-init" before that dominator
The problem with this is that "before" in the sense of dominators isn't sufficient; that only dictates ordering on the CPU the code is executing on. You need happens-before, i.e. the ordering visible to all CPUs, to ensure you don't have a race.
The user is responsible for ensuring there's a barrier between the allocation of the variable and the use, but if the auto-init is in a different place, you can't depend on the barrier the user wrote.
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https://reviews.llvm.org/D137707/new/
https://reviews.llvm.org/D137707
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