[PATCH] D14067: [FPEnv Core 02/14] Add FPEnv access flags to fast-math flags

[Sergey Dmitrouk via llvm-commits]

sdmitrouk added a comment.

In http://reviews.llvm.org/D14067#277179, @sdmitrouk wrote:

> In http://reviews.llvm.org/D14067#275220, @majnemer wrote:
>
> > Older bitcode would have to be auto-upgraded to add those flags onto older instructions.
>
>
> There is a compatibility issue. `kexc` and `kround` can be added when they are needed leaving regular behaviour for cases where these flags are not specified, they also have property of having all fast-math flags unset by default. Combination of `nexc` and `nrnd` flags corresponds to current behaviour and all new code that wants folding will need to include these flags explicitly. Or is this what you mean by saying `Older bitcode would have to be auto-upgraded to add those flags onto older instructions.`?


@majnemer, I guess you were talking about AutoUpgrade.cpp <http://www.llvm.org/docs/doxygen/html/AutoUpgrade_8cpp.html> rather than the issue I mentioned. I don't see a good way of handling this change, existing `.ll` files with FP instructions will change their meaning if not updated to include `nexc` and `nrnd`. I think such change isn't worth it. Is it? Or just keep `kexc` and `kround` (maybe rename it to `krnd` then)?


Repository:
  rL LLVM

http://reviews.llvm.org/D14067