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M. Zeeshan Siddiqui 70471f08ee
[Sema] Fix -Wunreachable-code false negative when operands differ only by implicit casts (#149972) 
## Motivation  
`-Wunreachable-code` missed—or in rare cases crashed on—tautological
comparisons such as

```cpp
x != 0 || x != 1.0   // always true
x == 0 && x == 1.0   // always false
```

when the *same* variable appears on both sides but one operand goes
through a floating‑rank promotion that is target‑dependent. On back‑ends
with **native half‑precision** (`_Float16` / `__fp16`) such as
AArch64 `+fullfp16`, no promotion occurs, so the cast stacks between the
two operands differ and the existing heuristic bails out.

## Technical description 
* **Extends `Expr::isSameComparisonOperand()`** – the helper now ignores
parentheses **and value‑preserving implicit casts**
(`CK_LValueToRValue`, floating‑rank `CK_FloatingCast`) before comparing
the underlying operands. This prevents floating‑rank promotions and
lvalue‑to‑rvalue conversions from blocking the unreachable‑code
diagnostic on targets with native FP16.
*No change needed in `CheckIncorrectLogicOperator`; it simply benefits
from the improved helper.*
* **Regression test** – `warn-unreachable_crash.cpp` updated to cover
both the promoted case (x86‑64) and the native‑half case
(AArch64 `+fullfp16`).
* **Docs** – release‑note bullet added under *Bug Fixes in This
Version*.

@ziqingluo-90 @yronglin Could you please review promptly? (feel free to
also merge it on my behalf) Thanks!

Fixes #149967

Co-authored-by: Zeeshan Siddiqui <mzs@ntdev.microsoft.com>
2025-07-31 09:21:59 +08:00
..
bindings
Revert "Move python binding tests to lit framework" (#149012)
2025-07-16 05:32:08 +01:00
cmake
[CMake][Release] Build with -ffat-lto-objects (#140381)
2025-07-29 15:33:49 -07:00
docs
[Sema] Fix -Wunreachable-code false negative when operands differ only by implicit casts (#149972)
2025-07-31 09:21:59 +08:00
examples
…
include
[AMDGPU] Add v_cvt_sr|pk_bf8|fp8_f16 gfx1250 instructions (#151415)
2025-07-30 17:24:45 -07:00
lib
[Sema] Fix -Wunreachable-code false negative when operands differ only by implicit casts (#149972)
2025-07-31 09:21:59 +08:00
runtime
…
test
[Sema] Fix -Wunreachable-code false negative when operands differ only by implicit casts (#149972)
2025-07-31 09:21:59 +08:00
tools
[LinkerWrapper] Fix -fsave-optimization-record default file (#149003)
2025-07-30 10:25:37 -04:00
unittests
[clang-format] Disable IntegerLiteralSeparator for C++ before c++14 (#151273)
2025-07-30 09:43:46 -07:00
utils
[AArch64][NEON] NEON intrinsic compilation error with -fno-lax-vector-conversion flag fix (#149329)
2025-07-30 10:56:14 +01:00
www
[NFC] [C++] [Modules] Mark P2115 as implemented and add test (#147489)
2025-07-08 18:36:53 +08:00
.clang-format
…
.clang-tidy
…
.gitignore
…
AreaTeamMembers.txt
…
CMakeLists.txt
Revert "Move python binding tests to lit framework" (#149012)
2025-07-16 05:32:08 +01:00
INSTALL.txt
…
LICENSE.TXT
…
Maintainers.rst
Propose new ClangIR Maintainer (#147365)
2025-07-09 11:15:23 -03:00
NOTES.txt
…
README.md
…

README.md

C language Family Front-end

Welcome to Clang.

This is a compiler front-end for the C family of languages (C, C++ and Objective-C) which is built as part of the LLVM compiler infrastructure project.

Unlike many other compiler frontends, Clang is useful for a number of things beyond just compiling code: we intend for Clang to be host to a number of different source-level tools. One example of this is the Clang Static Analyzer.

If you're interested in more (including how to build Clang) it is best to read the relevant websites. Here are some pointers: