llvm-project

70471f08 - [Sema] Fix -Wunreachable-code false negative when operands differ only by implicit casts (#149972)

[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>