[PATCH] Teach instcombine how to combine multiply of constant splat of known power-of-2

[Rafael Espíndola]

you explicitly test that things like

define i32 @MulTest3_i8(i32 %InVec)  {
entry:
  %0 = bitcast i32 %InVec to <4 x i8>
  %mul = mul <4 x i8> %0, <i8 4, i8 4, i8 2, i8 2>
  %1 = bitcast <4 x i8> %mul to i32
  ret i32 %1
}

are not optimized. Why is it not profitable to use

shl <4 x i8> %0, <i8 2, i8 2, i8 1, i8 1>

?
Cheers,
Rafael