Merging r251622:

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r251622 | vkalintiris | 2015-10-29 10:17:16 +0000 (Thu, 29 Oct 2015) | 17 lines

[mips] Check the register class before replacing materializations of zero with $zero in microMIPS.

Summary:
The microMIPS register class GPRMM16 does not contain the $zero register.
However, MipsSEDAGToDAGISel::replaceUsesWithZeroReg() would replace uses
of the $dst register:

  [d]addiu, $dst, $zero, 0

with the $zero register, without checking for membership in the register
class of the target machine operand.

Reviewers: dsanders

Subscribers: llvm-commits, dsanders

Differential Revision: http://reviews.llvm.org/D13984
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llvm-svn: 252158