Michael Kuperstein a52ddfa930 [DAGCombine] Produce better code for constant splats
This solves PR22276.
Splats of constants would sometimes produce redundant shuffles, sometimes ridiculously so (see the PR for details). Fold these shuffles into BUILD_VECTORs early on instead.

Differential Revision: http://reviews.llvm.org/D7093

Fixed recommit of r226811.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226816 91177308-0d34-0410-b5e6-96231b3b80d8
2015-01-22 13:07:28 +00:00
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