[all-commits] [llvm/llvm-project] 8a5715: [Sema] SequenceChecker: Fix handling of operator |...

[Bruno Ricci via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 8a571538dff6dbc1b7f4fed6aed8be7ec1a00a8d
      https://github.com/llvm/llvm-project/commit/8a571538dff6dbc1b7f4fed6aed8be7ec1a00a8d
  Author: Bruno Ricci <riccibrun at gmail.com>
  Date:   2019-12-22 (Sun, 22 Dec 2019)

  Changed paths:
    M clang/lib/Sema/SemaChecking.cpp
    M clang/test/Sema/warn-unsequenced.c
    M clang/test/SemaCXX/warn-unsequenced.cpp

  Log Message:
  -----------
  [Sema] SequenceChecker: Fix handling of operator ||, && and ?:

The current handling of the operators ||, && and ?: has a number of false
positive and false negative. The issues for operator || and && are:

1. We need to add sequencing regions for the LHS and RHS as is done for the
   comma operator. Not doing so causes false positives in expressions like
   `((a++, false) || (a++, false))` (from PR39779, see PR22197 for another
    example).

2. In the current implementation when the evaluation of the LHS fails, the RHS
   is added to a worklist to be processed later. This results in false negatives
   in expressions like `(a && a++) + a`.

Fix these issues by introducing sequencing regions for the LHS and RHS, and by
not deferring the visitation of the RHS.

The issues with the ternary operator ?: are similar, with the added twist that
we should not warn on expressions like `(x ? y += 1 : y += 2)` since exactly
one of the 2nd and 3rd expression is going to be evaluated, but we should still
warn on expressions like `(x ? y += 1 : y += 2) = y`.

Differential Revision: https://reviews.llvm.org/D57747

Reviewed By: rsmith