[RISCV] Fix std::advance slowness
Summary:
It seems std::advance template is treating "-MFI.getCalleeSavedInfo().size()"
as a large unsigned value", causing slowness.
Thanks to Henrik Gustafsson for reporting the issue.
Reviewers: asb
Reviewed By: asb
Subscribers: llvm-commits, rbar, johnrusso, simoncook, sabuasal, niosHD, kito-cheng, shiva0217, zzheng, edward-jones, mgrang, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe, PkmX, jocewei, asb
Differential Revision: https://reviews.llvm.org/D51148
llvm-svn: 340669