[PATCH] D55506: [RFC v2] Allow target to handle STRICT floating-point nodes

[Cameron McInally via Phabricator via llvm-commits]

cameron.mcinally added a comment.

> Well, mayRaise Exception is purely a MI level flag. I struggle to see where optimizations on the MI level would ever care about rounding modes in the sense you describe: note that currently, MI optimizations don't even know which operation an MI instruction performs -- if you don't even know whether you're dealing with addition or subtraction, why would you care which rounding mode the operation is performed in? MI transformations instead care about what I'd call "structural" properties of the operation: what are the operands, what is input vs. output, which memory may be accessed, which special registers may involved, which other side effects may the operation have. This is the type of knowledge you need for the types of transformations that are done on the MI level: mostly about moving instructions around, arriving at an optimal schedule, de-duplicating identical operations performed multiple times etc. (Even things like simply changing a register operand to a memory operand for the same operation cannot be done solely by common MI optimizations but require per-target support.)

Huh, this is interesting and was not clear to me a priori. After digging around a bit, I agree with you that almost all of the MI code is fine wrt rounding.


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https://reviews.llvm.org/D55506