[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

lib/Target/Mips/MipsISelDAGToDAG.cpp

@@ -202,8 +202,9 @@ SDNode* MipsDAGToDAGISel::Select(SDNode *Node) {
 #ifndef NDEBUG
   case ISD::LOAD:
   case ISD::STORE:
-    assert(cast<MemSDNode>(Node)->getMemoryVT().getSizeInBits() / 8 <=
-           cast<MemSDNode>(Node)->getAlignment() &&
+    assert((Subtarget.systemSupportsUnalignedAccess() ||
+            cast<MemSDNode>(Node)->getMemoryVT().getSizeInBits() / 8 <=
+            cast<MemSDNode>(Node)->getAlignment()) &&
            "Unexpected unaligned loads/stores.");
     break;
 #endif