[llvm] r340669 - [RISCV] Fix std::advance slowness

[Ana Pazos via llvm-commits]

Author: apazos
Date: Fri Aug 24 16:13:59 2018
New Revision: 340669

URL: http://llvm.org/viewvc/llvm-project?rev=340669&view=rev
Log:
 [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

Modified:
    llvm/trunk/lib/Target/RISCV/RISCVFrameLowering.cpp

Modified: llvm/trunk/lib/Target/RISCV/RISCVFrameLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/RISCV/RISCVFrameLowering.cpp?rev=340669&r1=340668&r2=340669&view=diff
==============================================================================
--- llvm/trunk/lib/Target/RISCV/RISCVFrameLowering.cpp (original)
+++ llvm/trunk/lib/Target/RISCV/RISCVFrameLowering.cpp Fri Aug 24 16:13:59 2018
@@ -148,8 +148,7 @@ void RISCVFrameLowering::emitEpilogue(Ma
   // 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();