On Tue, 13 May 2025, Jakub Jelinek wrote: > On Tue, May 13, 2025 at 10:40:16AM +0000, Tamar Christina wrote: > > That's true. The names are already optional, I can just drop the > > "requested" > > all together. > > > > I'll give it a few to give others a chance to commit and I'll respin > > dropping "requested" > > Is the intended behavior of the "weak" version that the compiler can > increase or decrease it based on command line options etc., or that it > must unroll at least N times but with command line options etc. it could > be something higher than that? > > Perhaps > #pragma GCC unroll 16 > vs. > #pragma GCC unroll >= 16 > or > #pragma GCC unroll 16+ > ? > As for keywords, I was worried about macros, but seems GCC unroll pragma > doesn't have macro expansion in the name nor arguments part, so when one > wants to macro expand the count, one needs to use _Pragma and create the > right expression as string literal.
I think the intent for the given case is that GCC unrolls the loop, but not as much as with -funroll-loops (factor 8 IIRC). But when vectorizing then the unroll request is satisfied already (given vectorization effectively unrolls). IMO it should be possible to just use #pramga GCC unroll for this. That does't do the limiting to 4 times unrolling, but leaves it to the (non-existent) cost modeling of the RTL unroller. I think we should avoid to overengineer this for PR116140 which is just a case where we do _not_ want further unrolling after vectorization. Richard.
