Nasty bug in ARMBaseInstrInfo::produceSameValue(). The MachineConstantPoolEntry

entries being compared may not be ARMConstantPoolValue. Without checking
whether they are ARMConstantPoolValue first, and if the stars and moons
are aligned properly, the equality test may return true (when the first few
words of two Constants' values happen to be identical) and very bad things can
happen.

rdar://9125354

llvm-svn: 128203