[PATCH] Fix MipsLongBranch pass to work when the code has inline assembly.

[Sasa Stankovic]

  I reordered instructions in the long branch to avoid the bug in GAS. When first of the symbols in %hi(label1 - label2) and %lo(label1 - label2) is defined before the two instructions, and the other symbol is defined between the two instructions, then GAS can sometime (for label1 - label2 close to -32768) wrongly calculate %hi(label1 - label2), by adding +1 when it is not needed. To avoid this, instead of

  $longbr:
      addiu $sp, $sp, -8
      sw $ra, 0($sp)
      bal $baltgt
      lui $at, %hi($tgt - $baltgt)
  $baltgt:
      addiu $at, $at, %lo($tgt - $baltgt)
      addu $at, $ra, $at
      lw $ra, 0($sp)
      jr $at
      addiu $sp, $sp, 8
  $fallthrough:

  the following sequence is used for long branch:

  $longbr:
      addiu $sp, $sp, -8
      sw $ra, 0($sp)
      lui $at, %hi($tgt - $baltgt)
      bal $baltgt
      addiu $at, $at, %lo($tgt - $baltgt)
  $baltgt:
      addu $at, $ra, $at
      lw $ra, 0($sp)
      jr $at
      addiu $sp, $sp, 8
  $fallthrough:

Hi mseaborn, dsanders,

http://reviews.llvm.org/D3089

CHANGE SINCE LAST DIFF
  http://reviews.llvm.org/D3089?vs=8305&id=8578#toc

Files:
  lib/Target/Mips/Mips64InstrInfo.td
  lib/Target/Mips/MipsAsmPrinter.cpp
  lib/Target/Mips/MipsAsmPrinter.h
  lib/Target/Mips/MipsInstrInfo.h
  lib/Target/Mips/MipsInstrInfo.td
  lib/Target/Mips/MipsLongBranch.cpp
  lib/Target/Mips/MipsMCInstLower.cpp
  lib/Target/Mips/MipsMCInstLower.h
  test/CodeGen/Mips/longbranch.ll
  test/CodeGen/Mips/micromips-long-branch.ll
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