[PATCH] D38300: [x86] Correct the implementation of isTruncateFree to be more accurate

[Craig Topper via Phabricator via llvm-commits]

craig.topper planned changes to this revision.
craig.topper added a comment.

I can't seem to fix the perf loss on this one benchmark. So I need to hold off on this.

It looks to be that in this particular case, the SLP vectorize was previously creating a v16i64->v16i8 truncate in AVX2 and we are no longer doing that. Attempts at fudging new entries into the cost model to lower the truncate cost (which was calculated at 11) haven't worked so far.


https://reviews.llvm.org/D38300