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
diff --git a/lib/Target/Mips/MipsMCInstLower.cpp b/lib/Target/Mips/MipsMCInstLower.cpp
index 6143eaa..37662e9 100644
--- a/lib/Target/Mips/MipsMCInstLower.cpp
+++ b/lib/Target/Mips/MipsMCInstLower.cpp
@@ -321,3 +321,29 @@
if (!TwoInstructions) MCInsts.push_back(Instr3);
}
+// Convert
+// "setgp01 $reg"
+// to
+// "lui $reg, %hi(_gp_disp)"
+// "addiu $reg, $reg, %lo(_gp_disp)"
+void MipsMCInstLower::LowerSETGP01(const MachineInstr *MI,
+ SmallVector<MCInst, 4>& MCInsts) {
+ const MachineOperand &MO = MI->getOperand(0);
+ assert(MO.isReg());
+ MCOperand RegOpnd = MCOperand::CreateReg(MO.getReg());
+ StringRef SymName("_gp_disp");
+ const MCSymbol *Sym = Ctx.GetOrCreateSymbol(SymName);
+ const MCSymbolRefExpr *MCSym;
+
+ MCInsts.resize(2);
+
+ MCSym = MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_Mips_ABS_HI, Ctx);
+ MCInsts[0].setOpcode(Mips::LUi);
+ MCInsts[0].addOperand(RegOpnd);
+ MCInsts[0].addOperand(MCOperand::CreateExpr(MCSym));
+ MCSym = MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_Mips_ABS_LO, Ctx);
+ MCInsts[1].setOpcode(Mips::ADDiu);
+ MCInsts[1].addOperand(RegOpnd);
+ MCInsts[1].addOperand(RegOpnd);
+ MCInsts[1].addOperand(MCOperand::CreateExpr(MCSym));
+}