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

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

1 files changed, 0 insertions, 27 deletions

diff --git a/lib/Target/Mips/MipsInstrInfo.cpp b/lib/Target/Mips/MipsInstrInfo.cpp
index 4dbd29e..573b31a 100644
--- a/lib/Target/Mips/MipsInstrInfo.cpp
+++ b/lib/Target/Mips/MipsInstrInfo.cpp
@@ -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;
-}