[PATCH] D42424: [InstCombine] Allow common type conversions to i8/i16

[Krzysztof Parzyszek via Phabricator via llvm-commits]

kparzysz added a comment.

The sensible thing to do would be to have a well-defined canonical form of the IR, instead of "the most strength-reduced".  This is an example why lack of it is only creating issues, and how having idiom-recognition that goes beyond a trivial "memcpy" or "memset" is notoriously difficult to maintain.  We could still have the "maximum combining", but after idiom recognition has run.

The code in the polynomial multiplication recognition has even evolved to have its own expression transformations to "undo" various changes that the combining had developed since the initial pattern matching was written.  I could change that code again, but unless there is a plan in place to fix this ongoing issue, this is not going to be a high priority for me.


https://reviews.llvm.org/D42424