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Ben Hamilton b4ab4b6317 [clang-tidy] ObjC ARC objects should not trigger performance-unnecessary-value-param 
Summary:
The following Objective-C code currently incorrectly triggers
clang-tidy's performance-unnecessary-value-param check:

```
% cat /tmp/performance-unnecessary-value-param-arc.m
void foo(id object) { }

clang-tidy /tmp/performance-unnecessary-value-param-arc.m
-checks=-\*,performance-unnecessary-value-param -- -xobjective-c
-fobjc-abi-version=2 -fobjc-arc
1 warning generated.
/src/llvm/tools/clang/tools/extra/test/clang-tidy/performance-unnecessary-value-param-arc.m:10:13:
warning: the parameter 'object' is copied for each invocation but only
used as a const reference; consider making it a const reference
[performance-unnecessary-value-param]
void foo(id object) { }
         ~~ ^
         const &
```

This is wrong for a few reasons:

1) Objective-C doesn't have references, so `const &` is not going to help
2) ARC heavily optimizes the "expensive" copy which triggers the warning

This fixes the issue by disabling the warning for non-C++, as well as
disabling it for objects under ARC memory management for
Objective-C++.

Fixes https://bugs.llvm.org/show_bug.cgi?id=32075

Test Plan: New tests added. Ran tests with `make -j12 check-clang-tools`.

Reviewers: alexfh, hokein

Reviewed By: hokein

Subscribers: stephanemoore, klimek, xazax.hun, cfe-commits, Wizard

Differential Revision: https://reviews.llvm.org/D42812

llvm-svn: 324097
 		2018-02-02 15:34:33 +00:00
..
change-namespace [change-namespace] Fix crash when injected base-class name is used in friend declarations. 2017-12-08 10:06:16 +00:00
clang-apply-replacements [CMake] Use PRIVATE in target_link_libraries for executables 2017-12-05 21:49:56 +00:00
clang-move [clang-move] Clever on handling header file which includes itself. 2018-01-31 12:12:29 +00:00
clang-query [CMake] Use PRIVATE in target_link_libraries for executables 2017-12-05 21:49:56 +00:00
clang-reorder-fields [CMake] Use PRIVATE in target_link_libraries for executables 2017-12-05 21:49:56 +00:00
clang-tidy [clang-tidy] ObjC ARC objects should not trigger performance-unnecessary-value-param 2018-02-02 15:34:33 +00:00
clang-tidy-vs Remove 'misc-pointer-and-integral-operation' clang-tidy check. The only cases 2016-10-21 21:50:28 +00:00
clangd [clangd] Remove a unused include. NFC 2018-02-02 11:25:38 +00:00
docs clang-tidy/rename_check.py misc-incorrect-roundings bugprone-incorrect-roundings 2018-01-30 15:12:24 +00:00
include-fixer [CMake] Use PRIVATE in target_link_libraries for executables 2017-12-05 21:49:56 +00:00
modularize [CMake] Use PRIVATE in target_link_libraries for executables 2017-12-05 21:49:56 +00:00
pp-trace [CMake] Use PRIVATE in target_link_libraries for executables 2017-12-05 21:49:56 +00:00
test [clang-tidy] ObjC ARC objects should not trigger performance-unnecessary-value-param 2018-02-02 15:34:33 +00:00
tool-template [CMake] Use PRIVATE in target_link_libraries for executables 2017-12-05 21:49:56 +00:00
unittests [clangd] Skip inline namespace when collecting scopes for index symbols. 2018-02-02 10:31:42 +00:00
.arcconfig [clang-tools-extra] Set up .arcconfig to point to new Diffusion CTE repository 2017-11-27 15:58:25 +00:00
.gitignore
…
CMakeLists.txt [cmake] Support running extra clang tool tests without static analyzer 2017-08-29 05:58:08 +00:00
CODE_OWNERS.TXT Updating the code owners list. 2015-09-02 20:00:41 +00:00
LICENSE.TXT Rename the clang-tidy safety module to be hicpp, for the High-Integrity C++ coding standard from PRQA. 2017-03-19 17:23:23 +00:00
README.txt Update references to new lists.llvm.org mailing lists. 2015-08-05 03:56:44 +00:00

README.txt 

//===----------------------------------------------------------------------===//
// Clang Tools repository
//===----------------------------------------------------------------------===//

Welcome to the repository of extra Clang Tools.  This repository holds tools
that are developed as part of the LLVM compiler infrastructure project and the
Clang frontend.  These tools are kept in a separate "extra" repository to
allow lighter weight checkouts of the core Clang codebase.

This repository is only intended to be checked out inside of a full LLVM+Clang
tree, and in the 'tools/extra' subdirectory of the Clang checkout.

All discussion regarding Clang, Clang-based tools, and code in this repository
should be held using the standard Clang mailing lists:
  http://lists.llvm.org/mailman/listinfo/cfe-dev

Code review for this tree should take place on the standard Clang patch and
commit lists:
  http://lists.llvm.org/mailman/listinfo/cfe-commits

If you find a bug in these tools, please file it in the LLVM bug tracker:
  http://llvm.org/bugs/