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...r from llvm. Don't worry. It is simple, MDNodes are meant to convey information about values that is optional. In other words, if a optimization pass is not aware if certain information communicated through MDNode then the pass should never lead to mis-compilation of the code. One example, is !notemoral hints. I could give other examples, but that is not the point. >>> For example, the metadata used by TBAA today is not safe. Imagine an >>> optimization pass which takes two allocas that are used in >>> non-overlaping regions and rewrites all uses of one to use the oth...

On Jan 27, 2012, at 11:20 AM, Devang Patel wrote: > > On Jan 26, 2012, at 2:10 PM, Dan Gohman wrote: > >> On Jan 26, 2012, at 12:54 PM, Devang Patel wrote: >>> >>> On Jan 26, 2012, at 11:15 AM, Dan Gohman wrote: >>> >>>> or what optimizers must do to preserve it. >>> >>> The number one reason behind metadata is to have a

...m. Don't worry. > > It is simple, MDNodes are meant to convey information about values that is optional. In other words, if a optimization pass is not aware if certain information communicated through MDNode then the pass should never lead to mis-compilation of the code. One example, is !notemoral hints. I could give other examples, but that is not the point. My understanding of metadata was that it can be discarded by optimizations, or any other transformations, without affecting correctness; however, discarded != ignored. That is, the optimization is expected to either update the metada...