[all-commits] [llvm/llvm-project] d0caf0: [flang] Avoid undefined behaviour when parsing for...

[David Spickett via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d0caf0d4857c2b00ba988f86703663685ec8697f
      https://github.com/llvm/llvm-project/commit/d0caf0d4857c2b00ba988f86703663685ec8697f
  Author: David Spickett <david.spickett at linaro.org>
  Date:   2025-07-09 (Wed, 09 Jul 2025)

  Changed paths:
    M flang/include/flang/Common/format.h

  Log Message:
  -----------
  [flang] Avoid undefined behaviour when parsing format expressions (#147539)

The test flang/test/Semantics/io08.f90 was failing when UBSAN was
enabled:
```
/home/david.spickett/llvm-project/flang/include/flang/Common/format.h:224:26: runtime error: signed integer overflow: 10 * 987654321098765432 cannot be represented in type 'int64_t' (aka 'long')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/david.spickett/llvm-project/flang/include/flang/Common/format.h:224:26
```
This is because the code was effectively:
* Take the risk of UB happening
* Check whether it happened or not

Which UBSAN is obviously not going to like. Instead of checking after
the fact, use llvm's helpers that catch overflow without actually doing
it.



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