[PATCH] D29000: [SelectionDAG] Teach getNode to simplify a couple easy cases of EXTRACT_SUBVECTOR

Craig Topper via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Sun Jan 22 19:26:08 PST 2017

craig.topper created this revision.

This teaches getNode to simplify extracting from Undef. This is similar to what is done for EXTRACT_VECTOR_ELT. It also adds support for extracting from CONCAT_VECTOR when we can reused one of the inputs to the concat. These seem like simple non-target specific optimizations.

For X86 we currently handle undef in extractSubvector, but not all EXTRACT_SUBVECTOR creations go through there.

Ultimately, my motivation here is to simplify extractSubvector and remove custom lowering for EXTRACT_SUBVECTOR since we don't do anything but handle undef and BUILD_VECTOR optimizations, but those should be DAG combines.



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