[X86] Reduce some patterns by using FP instructions for integer types even...

[X86] Reduce some patterns by using FP instructions for integer types even when AVX2 is available and execution domain fixing will do the right thing

We have quite a few cases of using FP instructions for integer operations when only AVX1 is available. Then we switch to integer instructions with AVX2. In a lot of these cases execution domain fixing will take care of turning FP instructions into integer if its profitable.

With this patch we just keep on using the FP instructions even with AVX2. I've only handled some cases that don't require messing with patterns that are defined in the instruction definition. Those will require more subtle multiclass work possibly involving null_frag, hasSideEffects = 0, etc.

Differential Revision: https://reviews.llvm.org/D58470

llvm-svn: 355361