The (seldom-used) TBI-aware optimization had a typo lying dormant since
it was first introduced, in r252573: when asking for demanded bits, it
told TLI that it was running after legalize, where the opposite was
true.
This is an important piece of information, that the demanded bits
analysis uses to make assumptions about the node. r301019 added such an
assumption, which was broken by the TBI combine.
Instead, pass the correct flags to TLO.
llvm-svn: 309323
AArch64 has the ability to use the top 8-bits of an "address" for extra
information, with the memory subsystem automatically masking them off for loads
and stores. When that's happening, we can sometimes skip masks on memory
operations in the compiler.
However, this requires the host OS and support stack to preserve those bits so
it can't be enabled everywhere. In principle iOS 8.0 and above do take the
required precautions and but we'll put it under a flag for now.
llvm-svn: 252573
Ahmed Bougacha