[LLVMdev] Handling Masked Vector Operations

Nadav Rotem nrotem at apple.com
Thu May 2 10:41:14 PDT 2013

On May 2, 2013, at 10:31 AM, dag at cray.com wrote:

> But is that really a legal transformation?  Clearly not all elements are
> known to be undef.

Hi David, 
This blog post explains the motivation for modeling undefined behavior:  http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html

The idea is that you want to optimize your code based on the premise that undefined behavior in C allows you to do anything you like (to the undefined value).

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