[PATCH] D57747: [Sema] SequenceChecker: Fix handling of operator ||, && and ?:

[Bruno Ricci via Phabricator via cfe-commits]

riccibruno created this revision.
riccibruno added reviewers: aaron.ballman, rsmith.
riccibruno added a project: clang.
Herald added a subscriber: cfe-commits.

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`.


Repository:
  rC Clang

https://reviews.llvm.org/D57747

Files:
  lib/Sema/SemaChecking.cpp
  test/Sema/warn-unsequenced.c
  test/SemaCXX/warn-unsequenced.cpp

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