[PATCH] D66983: [WebAssembly] Add wasm-specific vector shuffle builtin and intrinsic

[Thomas Lively via Phabricator via llvm-commits]

tlively added a comment.

The context for this CL is https://github.com/emscripten-core/emscripten/issues/9340. The code that does the undesirable optimization is around llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:18776. I think it is a reasonable assumption that what you put in is what you get out, especially if you're trying to trigger particular WebAssembly engine behavior that the backend should not really be reasoning about. Now perhaps users should not be reasoning about it either, but given that they are I think this patch is reasonable.


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https://reviews.llvm.org/D66983