[mips][mips64r6] [ls][dw][lr] are not available in MIPS32r6/MIPS64r6

Summary:
Instead the system is required to provide some means of handling unaligned
load/store without special instructions. Options include full hardware
support, full trap-and-emulate, and hybrids such as hardware support within
a cache line and trap-and-emulate for multi-line accesses.

MipsSETargetLowering::allowsUnalignedMemoryAccesses() has been configured to
assume that unaligned accesses are 'fast' on the basis that I expect few
hardware implementations will opt for pure-software handling of unaligned
accesses. The ones that do handle it purely in software can override this.

mips64-load-store-left-right.ll has been merged into load-store-left-right.ll

The stricter testing revealed a Bits!=Bytes bug in passByValArg(). This has
been fixed and the variables renamed to clarify the units they hold.

Reviewers: zoran.jovanovic, jkolek, vmedic

Reviewed By: vmedic

Differential Revision: http://reviews.llvm.org/D3872

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209512 91177308-0d34-0410-b5e6-96231b3b80d8
[mips][mips64r6] t(eq|ge|lt|ne)i and t(ge|lt)iu are not available in MIPS32r6/MIPS64r6

Summary: Depends on D3872

Reviewers: jkolek, zoran.jovanovic, vmedic

Reviewed By: vmedic

Differential Revision: http://reviews.llvm.org/D3891

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209513 91177308-0d34-0410-b5e6-96231b3b80d8
[mips] Work around inconsistency in llvm-mc's placement of fixup markers

Summary:
Add a second fixup table to MipsAsmBackend::getFixupKindInfo() to correctly
position llvm-mc's fixup placeholders for big-endian.

See PR19836 for full details of the issue. To summarize, the fixup placeholders
do not account for endianness properly and the implementations of
getFixupKindInfo() for each target are measuring MCFixupKindInfo.TargetOffset
from different ends of the instruction encoding to compensate.

Reviewers: jkolek, zoran.jovanovic, vmedic

Reviewed By: vmedic

Differential Revision: http://reviews.llvm.org/D3889

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209514 91177308-0d34-0410-b5e6-96231b3b80d8