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Roman Lebedev 46b8ea2fff
[clang-tidy] Add check for implicit widening of multiplication result 
Overflows are never fun.
In most cases (in most of the code), they are rare,
because usually you e.g. don't have as many elements.

However, it's exceptionally easy to fall into this pitfail
in code that deals with images, because, assuming 4-channel 32-bit FP data,
you need *just* ~269 megapixel image to case an overflow
when computing at least the total byte count.

In [[ https://github.com/darktable-org/darktable | darktable ]], there is a *long*, painful history of dealing with such bugs:
* https://github.com/darktable-org/darktable/pull/7740
* https://github.com/darktable-org/darktable/pull/7419
* eea1989f2c
* 70626dd95b
* https://github.com/darktable-org/darktable/pull/670
* 38c69fb1b2

and yet they clearly keep resurfacing still.

It would be immensely helpful to have a diagnostic for those patterns,
which is what this change proposes.

Currently, i only diagnose the most obvious case, where multiplication
is directly widened with no other expressions inbetween,
(i.e. `long r = (int)a * (int)b` but not even e.g. `long r = ((int)a * (int)b)`)
however that might be worth relaxing later.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D93822
 		2021-04-13 21:41:22 +03:00
..
clang-apply-replacements [clang-tools-extra] Prevent linking to duplicate .a libs and dylib 2020-06-17 19:00:26 +02:00
clang-change-namespace [clang-tooling] Prevent llvm::fatal_error on invalid CLI option 2021-01-29 10:15:06 +01:00
clang-doc [openmp] Add missing dependencies for OMP.h.inc after d90443b 2020-06-23 11:48:04 -04:00
clang-include-fixer [clang-include-fixer] Pre-reserve vector size. NFC 2021-02-03 08:30:45 +01:00
clang-move [SystemZ][z/OS][Windows] Add new OF_TextWithCRLF flag and use this flag instead of OF_Text 2021-04-06 07:23:31 -04:00
clang-query [clang-query] Fix help text after D91918 2021-03-03 15:57:49 +00:00
clang-reorder-fields [clang-tooling] Prevent llvm::fatal_error on invalid CLI option 2021-01-29 10:15:06 +01:00
clang-tidy [clang-tidy] Add check for implicit widening of multiplication result 2021-04-13 21:41:22 +03:00
clangd [clangd] Propagate data in diagnostics 2021-04-13 17:45:09 +02:00
docs [clang-tidy] Add check for implicit widening of multiplication result 2021-04-13 21:41:22 +03:00
modularize [SystemZ][z/OS][Windows] Add new OF_TextWithCRLF flag and use this flag instead of OF_Text 2021-04-06 07:23:31 -04:00
pp-trace [SystemZ][z/OS][Windows] Add new OF_TextWithCRLF flag and use this flag instead of OF_Text 2021-04-06 07:23:31 -04:00
test [clang-tidy] Add check for implicit widening of multiplication result 2021-04-13 21:41:22 +03:00
tool-template [OpenMP] "UnFix" layering problem with FrontendOpenMP 2020-04-07 14:41:18 -05:00
unittests [libtooling][clang-tidy] Fix compiler warnings in testcase [NFC] 2021-04-12 08:26:46 +02:00
.gitignore
…
CMakeLists.txt Add an explicit toggle for the static analyzer in clang-tidy 2020-09-10 10:48:17 -04:00
CODE_OWNERS.TXT [clangd] add CODE_OWNERS 2020-01-29 12:43:19 +01:00
LICENSE.TXT
…
README.txt
…

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/