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Add an option to use a virtual register as the global base register instead of

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reserving a physical register ($gp or $28) for that purpose.

This will completely eliminate loads that restore the value of $gp after every
function call, if the register allocator assigns a callee-saved register, or
eliminate unnecessary loads if it assigns a temporary register. 

example:

.cpload $25       // set $gp.
...
.cprestore 16     // store $gp to stack slot 16($sp).
...
jalr $25          // function call. clobbers $gp.
lw $gp, 16($sp)   // not emitted if callee-saved reg is chosen.
...
lw $2, 4($gp)
...
jalr $25          // function call.
lw $gp, 16($sp)   // not emitted if $gp is not live after this instruction.
...



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151402 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Akira Hatanaka
2012-02-24 22:34:47 +00:00
parent 120cfdf0e0
commit 648f00c2f0
18 changed files with 275 additions and 98 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Target/Mips/MipsInstrInfo.cpp
-27
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@@ -454,30 +454,3 @@ ReverseBranchCondition(SmallVectorImpl<MachineOperand> &Cond) const
return false;
}
/// getGlobalBaseReg - Return a virtual register initialized with the
/// the global base register value. Output instructions required to
/// initialize the register in the function entry block, if necessary.
///
unsigned MipsInstrInfo::getGlobalBaseReg(MachineFunction *MF) const {
MipsFunctionInfo *MipsFI = MF->getInfo<MipsFunctionInfo>();
unsigned GlobalBaseReg = MipsFI->getGlobalBaseReg();
if (GlobalBaseReg != 0)
return GlobalBaseReg;
// Insert the set of GlobalBaseReg into the first MBB of the function
MachineBasicBlock &FirstMBB = MF->front();
MachineBasicBlock::iterator MBBI = FirstMBB.begin();
MachineRegisterInfo &RegInfo = MF->getRegInfo();
const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
unsigned GP = IsN64 ? Mips::GP_64 : Mips::GP;
const TargetRegisterClass *RC
= IsN64 ? Mips::CPU64RegsRegisterClass : Mips::CPURegsRegisterClass;
GlobalBaseReg = RegInfo.createVirtualRegister(RC);
BuildMI(FirstMBB, MBBI, DebugLoc(), TII->get(TargetOpcode::COPY),
GlobalBaseReg).addReg(GP);
RegInfo.addLiveIn(GP);
MipsFI->setGlobalBaseReg(GlobalBaseReg);
return GlobalBaseReg;
}