[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
diff --git a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
index a816028..7441789 100644
--- a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
@@ -148,8 +148,7 @@
// Skip to before the restores of callee-saved registers
// FIXME: assumes exactly one instruction is used to restore each
// callee-saved register.
- MachineBasicBlock::iterator LastFrameDestroy = MBBI;
- std::advance(LastFrameDestroy, -MFI.getCalleeSavedInfo().size());
+ auto LastFrameDestroy = std::prev(MBBI, MFI.getCalleeSavedInfo().size());
uint64_t StackSize = MFI.getStackSize();