[TwoAddressInstructionPass] After commuting an instruction and before trying to look...

[TwoAddressInstructionPass] After commuting an instruction and before trying to look for more commutable operands, resample the number of operands.

The new instruciton might have less operands than the original instruction. If we don't resample, the next loop iteration might read an operand that doesn't exist.

X86 can commute blends to movss/movsd which reduces from 4 operands to 3. This happened in the test case that caused r354363 & company to be reverted. A reduced version of that has been committed here.

Really this whole checking for more commutable operands is a little fragile. It assumes that the new instructions operands are the same order and positions as the original except for the pair that was swapped. I don't know of anything that breaks this assumption today, but I've left a fixme. Fixing this will likely require an interface change.

llvm-svn: 354738