[all-commits] [llvm/llvm-project] 36c862: [BuildLibCalls] Add more noundef to library functions

[Juneyoung Lee via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 36c8621638d18c830efe2c6a2a6d0a0338b0f79d
      https://github.com/llvm/llvm-project/commit/36c8621638d18c830efe2c6a2a6d0a0338b0f79d
  Author: Juneyoung Lee <aqjune at gmail.com>
  Date:   2020-09-09 (Wed, 09 Sep 2020)

  Changed paths:
    M llvm/lib/Transforms/Utils/BuildLibCalls.cpp
    M llvm/test/Transforms/InferFunctionAttrs/annotate.ll

  Log Message:
  -----------
  [BuildLibCalls] Add more noundef to library functions

This patch follows D85345 and adds more noundef attributes to return values/arguments of library functions
that are mostly about accessing the file system or processes.

A few functions like `chmod` or `times` use typedef `mode_t` and `clock_t`.
They are neither struct nor union, so they cannot contain undef even if they're lowered to iN in IR. So, it is fine to add noundef to them.

- clock_t's actual type is size_t (C17, 7.27.1.3), so it isn't struct or union.

- For mode_t, either int or long is used in practice because programmers use bit manipulation. So, I think it is okay that it's never aggregate in practice.

After this patch, the remaining library functions are those that eagerly participate in optimizations: they can be removed, reordered, or
introduced by a transformation from primitive IR operations.
For them, a few testings is needed, since it may not be valid to add noundef anymore even if C standard says it's okay.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D85894