Gui Andrade 10264a1b21 Introduce noundef attribute at call sites for stricter poison analysis ...

This change adds a new IR noundef attribute, which denotes when a function call argument or return val may never contain uninitialized bits.

In MemorySanitizer, this attribute enables optimizations which decrease instrumented code size by up to 17% (measured with an instrumented build of clang) . I'll introduce the change allowing msan to take advantage of this information in a separate patch.

Differential Revision: https://reviews.llvm.org/D81678

2021-03-04 12:15:12 -08:00

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