If the condition of a select is also a select, both with the same arguments: first a non-zero constant, then a zero constant, then the outer select is equivalent to the inner one and can thus be replaced by the result of the inner select (which is its own condition). Note: this is a special case of: SEL(SEL(x, C, 0), y, z) --> SEL(x, y, z) and without this patch we'll have: t = SEL(x, C, 0) r = SEL(t, C, 0) simplified into: t = SEL(x, C, 0) // possibly unused now r = SEL(x, C, 0) but the present patch do t = SEL(x, C, 0) r = t In other words, functionally, the result is the same but now the result is taken from the first instruction. Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>