[X86][SSE] Enable commutation for SSE immediate blend instructions

Patch to allow (v)blendps, (v)blendpd, (v)pblendw and vpblendd instructions to be commuted - swaps the src registers and inverts the blend mask.

This is primarily to improve memory folding (see new tests), but it also improves the quality of shuffles (see modified tests).

Differential Revision: http://reviews.llvm.org/D6015



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221313 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "[Reassociate] Canonicalize negative constants out of expressions."

This reverts commit r221171.

It performs this invalid transformation:
-  %div.i = urem i64 -1, %add
-  %sub.i = sub i64 -2, %div.i
+  %div.i = urem i64 1, %add
+  %sub.i1 = add i64 %div.i, -2

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221317 91177308-0d34-0410-b5e6-96231b3b80d8
Analysis: Make isSafeToSpeculativelyExecute fire less for divides

Divides and remainder operations do not behave like other operations
when they are given poison: they turn into undefined behavior.

It's really hard to know if the operands going into a div are or are not
poison.  Because of this, we should only choose to speculate if there
are constant operands which we can easily reason about.

This fixes PR21412.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221318 91177308-0d34-0410-b5e6-96231b3b80d8