Merging r366660 and r367306:

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r366660 | rksimon | 2019-07-21 21:04:44 +0200 (Sun, 21 Jul 2019) | 3 lines

[X86] SimplifyDemandedVectorEltsForTargetNode - Move SUBV_BROADCAST narrowing handling. NFCI.

Move the narrowing of SUBV_BROADCAST to where we handle all the other opcodes.
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r367306 | rksimon | 2019-07-30 13:35:13 +0200 (Tue, 30 Jul 2019) | 5 lines

[X86][AVX] SimplifyDemandedVectorElts - handle extraction from X86ISD::SUBV_BROADCAST source (PR42819)

PR42819 showed an issue that we couldn't handle the case where we demanded a 'sub-sub-vector' of the SUBV_BROADCAST 'sub-vector' source.

This patch recognizes these cases and extracts the sub-sub-vector instead of trying to broadcast to a type smaller than the 'sub-vector' source. 
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llvm-svn: 367991