[X86] Block commuting operand 1 of FMA*_Int instructions in...

[X86] Block commuting operand 1 of FMA*_Int instructions in findThreeSrcCommutedOpIndices. Remove uncommutable returns from getThreeSrcCommuteCase/getFMA3OpcodeToCommuteOperands.

We should be blocking the operand while we are in the routine that tries to find commutable operand indices. Doing it later means we might have missed out on another valid set of operands we could have commuted.

The intrinsic case was the only case that could really prevent commuting in getFMA3OpcodeToCommuteOperands. All the other cases in getThreeSrcCommuteCase were not reachable conditions as they were protected by findThreeSrcCommutedOpIndices.

With that abort case pushed earlier, we can remove all the abort checks and replace with asserts.

llvm-svn: 335446