[PATCH] D121670: [RISCV] Add zihintntl instructions

Tue Mar 14 03:09:59 PDT 2023

asb added a comment.

In D121670#4192158 <https://reviews.llvm.org/D121670#4192158>, @joshua-arch1 wrote:

> It seems that llvm implementation is different from Binutils/GCC. Binutils didn't regard ntl instructions as aliases of add since encoding space is reserved for HINT instructions.

How does this different implementation approach show up in terms of user-visible behaviour?

Looking at the ISA spec, I think the use of the term "reserved" with respect to hint instructions is unfortunate, because I don't think the intended meaning isn't that they are considered a "reserved" encoding as defined in the categories of instructions, as otherwise it would be legal for implementations to trap when encountering a hint, making them impossible to deploy in a backward compatible way.

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https://reviews.llvm.org/D121670