PowerPC subtargets prior to Power9 use the 'legacy' itinerary way to
provide scheduling information. This patch re-writes the tablegen file
to define the scheduling information in the new SchedModel way, which
can bring improvements to some benchmarks.
Reviewed By: shchenz
Differential Revision: https://reviews.llvm.org/D154488
In `PPCInstrInfo::optimizeCompareInstr` we seek opportunities to fold `cmp(d|w)` and `subf` as an `subf.`. However, if `subf.` gets overflow, `cr0` can't reflect the correct order, violating the semantics of `cmp(d|w)`.
Fixed https://bugs.llvm.org/show_bug.cgi?id=47830.
Reviewed By: #powerpc, nemanjai
Differential Revision: https://reviews.llvm.org/D90156