Add a test case for r208252. Prior to r208252, the FMA 231 family was marked as isCommutable. However the memory variants of this family are not commutable. Therefore, we did not implemented the findCommutedOpIndices for those variants and missed that the default implementation (more or less: commute indices 1 and 2) was firing behind our back. As a result, as demonstrated in the test case before the fix, we were transforming a = b * c + a into a = a * c + b.
; RUN: llc -fp-contract=fast -mattr=+fma -disable-cgp < %s -o - | FileCheck %s
; Check that the 2nd and 3rd arguments of fmaXXX231 reg1, reg2, mem3 are not commuted.
; <rdar://problem/16800495> 
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx"

; CHECK-LABEL: test1:
; %arg lives in xmm0 and it shouldn't be redefined until it is used in the FMA.
; CHECK-NOT {{.*}}, %xmm0
; %addr lives in rdi.
; %addr2 lives in rsi.
; CHECK: vmovss (%rsi), [[ADDR2:%xmm[0-9]+]]
; The assembly syntax is in the reverse order.
; CHECK: vfmadd231ss (%rdi), [[ADDR2]], %xmm0
define void @test1(float* %addr, float* %addr2, float %arg) {
entry:
  br label %loop

loop:
  %sum0 = phi float [ %fma, %loop ], [ %arg, %entry ]
  %addrVal = load float* %addr, align 4
  %addr2Val = load float* %addr2, align 4
  %fmul = fmul float %addrVal, %addr2Val
  %fma = fadd float %sum0, %fmul
  br i1 true, label %exit, label %loop

exit:
  store float %fma, float* %addr, align 4
  ret void
}