On 09/24/2010 10:10 AM, Paulo J. Matos wrote:
The rules currently take the shape:
,----
| (define_expand "umulqihi3"
`----
These rules were created in gcc42 and the idea was that we can use smult
instead of umult whenever RAH (MSW of the result) is not used
afterwards. The 2nd argument of make_mulqihi3 determines if we emit an
smult instead of an umult.
You can use mul<mode>3 for non-widening multiplication, which would
always use smult, and {u,}mul<mode1><mode2>3 for widening multiplication
which has to use smult or umult for correctness. That's how i386
chooses between multi-operand imul (non-widening), single-operand imul
(widening signed) and single-operand mul (widening unsigned). Note that
the i386 ISA lacks a non-widening unsigned multiplication exactly
because it's pointless.
Or are you already doing that?
Paolo
