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[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
This commit is contained in:
Ana Pazos 2018-08-24 23:13:59 +00:00
parent 673412e3fa
commit 61b28ede75
1 changed files with 1 additions and 2 deletions
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3
llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
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@ -148,8 +148,7 @@ void RISCVFrameLowering::emitEpilogue(MachineFunction &MF,
// 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();