Nikita Popov b9bba6ca9f [BasicAA] Track nuw through decomposed expressions (#106512) ...

When we decompose the GEP offset expression, and the arithmetic is not
performed using nuw operations, we cannot retain the nuw flag on the
decomposed GEP.

For example, if we have `gep nuw p, (a-1)`, this is not at all the same
as `gep nuw (gep nuw p, a), -1`.

Fix this by tracking NUW through linear expression decomposition,
similarly to what we already do for the NSW flag.

This fixes the miscompilation reported in
https://github.com/llvm/llvm-project/pull/105496#issuecomment-2315322220.

2024-09-02 12:11:03 +02:00

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