[PATCH] D81728: [InstCombine] Add target-specific inst combining

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D81728#2089644 <https://reviews.llvm.org/D81728#2089644>, @Flakebi wrote:

> This combines instructions, so I think it belongs into the InstCombine pass. On the other hand, the f16 form of the intrinsics is not available on all targets, so this combination cannot be applied unconditionally but it needs to be gated depending on the target.


The fact that this pass recognizes target-specific intrinsics at all is widely regarded as a mistake:
http://lists.llvm.org/pipermail/llvm-dev/2016-July/102317.html

Target-specific transforms should look first at codegen combiners (SDAG or GlobalISel). If that's too late, consider a target-specific IR codegen pass (I think AMDGPU has a few examples of this already). If that's still too late, write a generic IR transform pass that accesses TTI?


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https://reviews.llvm.org/D81728