Merging r368517, r368518, r368519, and r368554:

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r368517 | lebedevri | 2019-08-10 21:28:12 +0200 (Sat, 10 Aug 2019) | 1 line

[NFC][InstCombine] Tests for shift amount reassociation in bittest with shift of const
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r368518 | lebedevri | 2019-08-10 21:28:44 +0200 (Sat, 10 Aug 2019) | 5 lines

[InstCombine] Shift amount reassociation in bittest: drop pointless one-use restriction

That one-use restriction is not needed for correctness - we have already
ensured that one of the shifts will go away, so we know we won't increase
the instruction count. So there is no need for that restriction.
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r368519 | lebedevri | 2019-08-10 21:28:54 +0200 (Sat, 10 Aug 2019) | 5 lines

[InstCombine] Shift amount reassociation in bittest: relax one-use check when shifting constant

If one of the values being shifted is a constant, since the new shift
amount is known-constant, the new shift will end up being constant-folded
so, we don't need that one-use restriction then.
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r368554 | lebedevri | 2019-08-12 13:28:02 +0200 (Mon, 12 Aug 2019) | 6 lines

[InstCombine] foldShiftIntoShiftInAnotherHandOfAndInICmp(): avoid constantexpr pitfail (PR42962)

Instead of matching value and then blindly casting to BinaryOperator
just to get the opcode, just match instruction and do no cast.

Fixes https://bugs.llvm.org/show_bug.cgi?id=42962
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llvm-svn: 368673