[PATCH] D20327: [InstCombine] transform multiplication overflow check written as a > (UINT_MAX /u b) to umul.with.overflow

[Sanjoy Das via llvm-commits]

sanjoy added a comment.

The conclusions / guidelines decided from the earlier work were

1. The optimizer should not introduce these intrinsics early in the pipeline, since there are passes that don't understand them yet.
2. CGP should do a best-effort replacement of arithmetic with overflow intrinsics (i.e. this change should live in CGP).
3. If the programmer really would have liked the codegen to use overflow bits in the CPU flags, then she need to use ` __builtin_umull_overflow` etc. directly.

@regehr is there some specific reason it helps to canonicalize like this?


http://reviews.llvm.org/D20327