On 17/08/12 15:47, Richard Earnshaw wrote:
If we don't have a 16x16->64 mult operation then after step 1 we'll
still have a MULT_EXPR, not a WIDEN_MULT_EXPR, so when we reach step2
there's nothing to short circuit.
Unless, of course, you're expecting us to get
step1 -> 16x16->32 widen mult
step2 -> widen64(step1) + acc64
No, given a u16xu16->u64 operation in the code, and that the arch
doesn't have such an opcode, I'd expect to get
step1 -> (u32)u16 x (u32)u16 -> u64
Likewise, 8x8->32 might give (16)8x(16)8->32.
The code can't see that the widening operation is non-optimal without
looking beyond into its inputs.
Andrew
