On 10/18/24 7:12 AM, Craig Blackmore wrote:
If riscv_vector::expand_block_move is generating a straight-line memcpy
using a predicated store, it tries to use a smaller LMUL to reduce
register pressure if it still allows an entire transfer.
This happens in the inner loop of riscv_vector::expand_block_move,
however, the vmode chosen by this loop gets overwritten later in the
function, so I have added the missing break from the outer loop.
I have also addressed a couple of issues with the conditions of the if
statement within the inner loop.
The first condition did not make sense to me:
```
TARGET_MIN_VLEN * lmul <= nunits * BITS_PER_UNIT
```
I think this was supposed to be checking that the length fits within the
given LMUL, so I have changed it to do that.
Yea, this just looks broken.
The second condition:
```
/* Avoid loosing the option of using vsetivli . */
&& (nunits <= 31 * lmul || nunits > 31 * 8)
```
seems to imply that lmul affects the range of AVL immediate that
vsetivli can take but I don't think that is correct. Anyway, I don't
think this condition is necessary because if we find a suitable mode we
should stick with it, regardless of whether it allowed vsetivli, rather
than continuing to try larger lmul which would increase register
pressure or smaller potential_ew which would increase AVL. I have
removed this condition.
I think it's just trying to micro-optimize, but it may not be a
particularly good tradeoff. That load immediate should be incredibly
cheap on a modern design. Generating a smaller LMUL seems like the
better tradeoff. Simplifies the code as well.
Pushed to the trunk.
Thanks!
jeff
