[PATCH] D142907: LangRef: Add "dynamic" option to "denormal-fp-math"

[Kevin P. Neal via Phabricator via cfe-commits]

kpn added a comment.

What's the plan for tying this to strictfp? Because I don't it should be tied to cases where we use the constrained intrinsics but the exceptions are ignored and the default rounding is in stated. Those instructions are supposed to behave the same as the non-constrained instructions. So keying off the presence of the strictfp attribute on the function definition, or the (equivalent) presence of constrained intrinsics, would be too simple.

I don't see an obvious connection between denormals and exception behavior, and the rounding mode has the same problem. It would be surprising if changing the rounding mode changed denormal handling or optimization even when the new rounding mode would have identical results. It would also be surprising if changing the rounding mode back to the default round-to-nearest changed how denormals are handled.

Would we get different denormal behavior with a clang flag vs using a #pragma at the top of a source file? That seems surprising as well.

In the abstract I can see lumping in denormal handing with the rest of the FP environment handling. But in the LLVM context I don't see how we can tie use of the constrained intrinsics to denormals.


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  https://reviews.llvm.org/D142907/new/

https://reviews.llvm.org/D142907