You don't need to multiply by zero; there are comparison operations which will generate a mask value which can then be used to select the appropriate value (`vsel` for altivec, `_mm_blend_ps` for sse4, or a combination of `_mm_and_ps` / `_mm_andnot_ps` / `_mm_or_ps` for ssse3 and earlier)

At least on Xbox 360 / Cell, high performance number crunching code would often compute more than needed (ie: both the if-case and else-case) and then use a branchless select to pick the right result. It may seem like a waste but it was faster than the combination of branch misprediction as well as shuffling values from one register file to another to be able to do scalar comparisons.