[all-commits] [llvm/llvm-project] 117074: [inferattrs] Don't infer lib func attributes for n...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 11707435ccb44a9377bfed407453e0646a159636
      https://github.com/llvm/llvm-project/commit/11707435ccb44a9377bfed407453e0646a159636
  Author: Philip Reames <listmail at philipreames.com>
  Date:   2021-04-16 (Fri, 16 Apr 2021)

  Changed paths:
    M llvm/lib/Transforms/IPO/InferFunctionAttrs.cpp
    A llvm/test/Transforms/InferFunctionAttrs/nobuiltin.ll

  Log Message:
  -----------
  [inferattrs] Don't infer lib func attributes for nobuiltin functions

If we have a nobuiltin function, we can't assume we know anything about the implementation.

I noticed this when tracing through a log from an in the wild miscompile (https://github.com/emscripten-core/emscripten/issues/9443) triggered after 8666463.  We were incorrectly assuming that a custom allocator could not free.  (It's not clear yet this is the only problem in said issue.)

I also noticed something similiar mentioned in the commit message of ab243e when scrolling back through history.  Through, from what I can tell, that commit fixed symptom not root cause.

The interface we have for library function detection is extremely error prone, but given the interaction between ``nobuiltin`` decls and ``builtin`` callsites, it's really hard to imagine something much cleaner.  I may iterate on that, but it'll be invasive enough I didn't want to hold an obvious functional fix on it.