[PATCH] D126273: [DAGCombiner][VP] Add DAGCombine for merging VP_FADD and VP_FMUL to VP_FMA.

[Simon Moll via Phabricator via llvm-commits]

simoll added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:23061
+      return false;
+    return AllowFusionGlobally || N->getFlags().hasAllowContract();
+  };
----------------
simoll wrote:
> RKSimon wrote:
> > It'd be very useful if we pulled stuff like this out and shared it between all the various FMA generating combines.
> Yes. It is possible to lift the existing DAGCombiner Patterns to work on VP SDNodes as well as on regular SDNodes.
> I've implemented this in the LLVM stack for SX-Aurora under the LLVM license, ie it could be upstreamed:
> 
> https://github.com/sx-aurora-dev/llvm-project/blob/feature/generalized_pattern_rewriting/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp#L13859
> 
> You could rephrase this patch using the generalized pattern-rewriting technique. I'd happy to help with that!
> 
> The same applies to https://reviews.llvm.org/D121187
Some more info on the generalized pattern-matching thing:

The [visitFADDForFMACombine function](https://github.com/sx-aurora-dev/llvm-project/blob/feature/generalized_pattern_rewriting/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp#L13859) is templatized. The template parameter abstracts away the actual matching and SDNode creation. The flow of the code is the same (SDNode matching and creation is re-directed through the matcher class, that's all).

The templated function is instantiated twice, once with the [EmptyMatchContext for regular SDNodes](https://github.com/sx-aurora-dev/llvm-project/blob/feature/generalized_pattern_rewriting/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp#L824) and once with the [VPMatchContext for VP-SDNodes](https://github.com/sx-aurora-dev/llvm-project/blob/feature/generalized_pattern_rewriting/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp#L877).




Repository:
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  https://reviews.llvm.org/D126273/new/

https://reviews.llvm.org/D126273