Merging r371305 and r371307:

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r371305 | nikic | 2019-09-07 14:03:48 +0200 (Sat, 07 Sep 2019) | 1 line

[X86] Add test for PR43230; NFC
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r371307 | nikic | 2019-09-07 14:13:44 +0200 (Sat, 07 Sep 2019) | 9 lines

[X86] Fix pshuflw formation from repeated shuffle mask (PR43230)

Fix for https://bugs.llvm.org/show_bug.cgi?id=43230.

When creating PSHUFLW from a repeated shuffle mask, we have to apply
the checks to the repeated mask, not the original one. For the test
case from PR43230 the inspected part of the original mask is all undef.

Differential Revision: https://reviews.llvm.org/D67314
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llvm-svn: 371378