[PATCH] D101494: [SimplifyCFG] Ignore ephemeral values when counting insts for threading
Roman Lebedev via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Thu Apr 29 10:06:45 PDT 2021
lebedev.ri added a comment.
In D101494#2726074 <https://reviews.llvm.org/D101494#2726074>, @nikic wrote:
> Unless I'm missing something, this has a cache invalidation issue and will likely lead to non-deterministic builds. Say you have a dead block with an assume, which gets added to ephemeral values. Then that block and the instructions in it are removed. Now EphValues contains dangling pointers. Then new instructions get allocated and reuse the same memory. Now EphValues claims that values are ephemeral that aren't ephemeral.
It's basically the same problem we have/had with `LoopHeaders`, yep.
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https://reviews.llvm.org/D101494/new/
https://reviews.llvm.org/D101494
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