[PATCH][v2] Fall back to single-lane SLP before falling back to no SLP

The following changes the fallback to disable SLP when any of the discovered SLP instances failed to pass vectorization checking into a fallback that emulates what no SLP would do with SLP - force single-lane discovery for all instances. The patch does not remove the final fallback to disable SLP

[PATCH][v2] Fall back to single-lane SLP before falling back to no SLP

The following changes the fallback to disable SLP when any of the discovered SLP instances failed to pass vectorization checking into a fallback that emulates what no SLP would do with SLP - force single-lane discovery for all instances. The patch does not remove the final fallback to disable SLP