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[mips] Optimize long branch for MIPS64 by removing %higher and %highest.

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%higher and %highest can have non-zero values only for offsets greater
than 2GB, which is highly unlikely, if not impossible when compiling a
single function. This makes long branch for MIPS64 3 instructions smaller.

Differential Revision: http://llvm-reviews.chandlerc.com/D3281.diff


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209678 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sasa Stankovic 2014-05-27 18:53:06 +00:00
parent 41087d99df
commit 95ce098219
6 changed files with 30 additions and 46 deletions
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8
lib/Target/Mips/Mips64InstrInfo.td
View File

@ -245,16 +245,12 @@ let isCodeGenOnly = 1, rs = 0, shamt = 0 in {
"sll\t$rd, $rt, 0", [], II_SLL>;
}
// We need the following two pseudo instructions to avoid offset calculation for
// We need the following pseudo instruction to avoid offset calculation for
// long branches. See the comment in file MipsLongBranch.cpp for detailed
// explanation.
// Expands to: lui $dst, %highest($tgt - $baltgt)
def LONG_BRANCH_LUi64 : PseudoSE<(outs GPR64Opnd:$dst),
(ins brtarget:$tgt, brtarget:$baltgt), []>;
// Expands to: daddiu $dst, $src, %PART($tgt - $baltgt)
// where %PART may be %higher, %hi or %lo, depending on the relocation kind
// where %PART may be %hi or %lo, depending on the relocation kind
// that $tgt is annotated with.
def LONG_BRANCH_DADDiu : PseudoSE<(outs GPR64Opnd:$dst),
(ins GPR64Opnd:$src, brtarget:$tgt, brtarget:$baltgt), []>;

1
lib/Target/Mips/MipsAsmPrinter.cpp
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@ -958,7 +958,6 @@ void MipsAsmPrinter::NaClAlignIndirectJumpTargets(MachineFunction &MF) {
bool MipsAsmPrinter::isLongBranchPseudo(int Opcode) const {
return (Opcode == Mips::LONG_BRANCH_LUi
|| Opcode == Mips::LONG_BRANCH_ADDiu
|| Opcode == Mips::LONG_BRANCH_LUi64
|| Opcode == Mips::LONG_BRANCH_DADDiu);
}

36
lib/Target/Mips/MipsLongBranch.cpp
View File

@ -64,7 +64,7 @@ namespace {
: MachineFunctionPass(ID), TM(tm),
IsPIC(TM.getRelocationModel() == Reloc::PIC_),
ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()),
LongBranchSeqSize(!IsPIC ? 2 : (ABI == MipsSubtarget::N64 ? 13 : 9)) {}
LongBranchSeqSize(!IsPIC ? 2 : (ABI == MipsSubtarget::N64 ? 10 : 9)) {}
const char *getPassName() const override {
return "Mips Long Branch";
@ -324,10 +324,7 @@ void MipsLongBranch::expandToLongBranch(MBBInfo &I) {
// $longbr:
// daddiu $sp, $sp, -16
// sd $ra, 0($sp)
// lui64 $at, %highest($tgt - $baltgt)
// daddiu $at, $at, %higher($tgt - $baltgt)
// dsll $at, $at, 16
// daddiu $at, $at, %hi($tgt - $baltgt)
// daddiu $at, $zero, %hi($tgt - $baltgt)
// dsll $at, $at, 16
// bal $baltgt
// daddiu $at, $at, %lo($tgt - $baltgt)
@ -339,10 +336,20 @@ void MipsLongBranch::expandToLongBranch(MBBInfo &I) {
// $fallthrough:
//
// TODO: %highest and %higher can have non-zero values only when the
// offset is greater than 4GB, which is highly unlikely. Replace
// them (and the following instructon that shifts $at by 16) with the
// instruction that sets $at to zero.
// We assume the branch is within-function, and that offset is within
// +/- 2GB. High 32 bits will therefore always be zero.
// Note that this will work even if the offset is negative, because
// of the +1 modification that's added in that case. For example, if the
// offset is -1MB (0xFFFFFFFFFFF00000), the computation for %higher is
//
// 0xFFFFFFFFFFF00000 + 0x80008000 = 0x000000007FF08000
//
// and the bits [47:32] are zero. For %highest
//
// 0xFFFFFFFFFFF00000 + 0x800080008000 = 0x000080007FF08000
//
// and the bits [63:48] are zero.
Pos = LongBrMBB->begin();
@ -350,16 +357,9 @@ void MipsLongBranch::expandToLongBranch(MBBInfo &I) {
.addReg(Mips::SP_64).addImm(-16);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::SD)).addReg(Mips::RA_64)
.addReg(Mips::SP_64).addImm(0);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_LUi64),
Mips::AT_64).addMBB(TgtMBB).addMBB(BalTgtMBB);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_DADDiu),
Mips::AT_64).addReg(Mips::AT_64).addMBB(TgtMBB, MipsII::MO_HIGHER)
.addMBB(BalTgtMBB);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::DSLL), Mips::AT_64)
.addReg(Mips::AT_64).addImm(16);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_DADDiu),
Mips::AT_64).addReg(Mips::AT_64).addMBB(TgtMBB, MipsII::MO_ABS_HI)
.addMBB(BalTgtMBB);
Mips::AT_64).addReg(Mips::ZERO_64)
.addMBB(TgtMBB, MipsII::MO_ABS_HI).addMBB(BalTgtMBB);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::DSLL), Mips::AT_64)
.addReg(Mips::AT_64).addImm(16);

23
lib/Target/Mips/MipsMCInstLower.cpp
View File

@ -162,16 +162,16 @@ MCOperand MipsMCInstLower::createSub(MachineBasicBlock *BB1,
}
void MipsMCInstLower::
lowerLongBranchLUi(const MachineInstr *MI, MCInst &OutMI, int Opcode,
MCSymbolRefExpr::VariantKind Kind) const {
OutMI.setOpcode(Opcode);
lowerLongBranchLUi(const MachineInstr *MI, MCInst &OutMI) const {
OutMI.setOpcode(Mips::LUi);
// Lower register operand.
OutMI.addOperand(LowerOperand(MI->getOperand(0)));
// Create %hi($tgt-$baltgt) or %highest($tgt-$baltgt).
// Create %hi($tgt-$baltgt).
OutMI.addOperand(createSub(MI->getOperand(1).getMBB(),
MI->getOperand(2).getMBB(), Kind));
MI->getOperand(2).getMBB(),
MCSymbolRefExpr::VK_Mips_ABS_HI));
}
void MipsMCInstLower::
@ -185,7 +185,7 @@ lowerLongBranchADDiu(const MachineInstr *MI, MCInst &OutMI, int Opcode,
OutMI.addOperand(LowerOperand(MO));
}
// Create %lo($tgt-$baltgt), %hi($tgt-$baltgt) or %higher($tgt-$baltgt).
// Create %lo($tgt-$baltgt) or %hi($tgt-$baltgt).
OutMI.addOperand(createSub(MI->getOperand(2).getMBB(),
MI->getOperand(3).getMBB(), Kind));
}
@ -196,11 +196,7 @@ bool MipsMCInstLower::lowerLongBranch(const MachineInstr *MI,
default:
return false;
case Mips::LONG_BRANCH_LUi:
lowerLongBranchLUi(MI, OutMI, Mips::LUi, MCSymbolRefExpr::VK_Mips_ABS_HI);
return true;
case Mips::LONG_BRANCH_LUi64:
lowerLongBranchLUi(MI, OutMI, Mips::LUi64,
MCSymbolRefExpr::VK_Mips_HIGHEST);
lowerLongBranchLUi(MI, OutMI);
return true;
case Mips::LONG_BRANCH_ADDiu:
lowerLongBranchADDiu(MI, OutMI, Mips::ADDiu,
@ -208,10 +204,7 @@ bool MipsMCInstLower::lowerLongBranch(const MachineInstr *MI,
return true;
case Mips::LONG_BRANCH_DADDiu:
unsigned TargetFlags = MI->getOperand(2).getTargetFlags();
if (TargetFlags == MipsII::MO_HIGHER)
lowerLongBranchADDiu(MI, OutMI, Mips::DADDiu,
MCSymbolRefExpr::VK_Mips_HIGHER);
else if (TargetFlags == MipsII::MO_ABS_HI)
if (TargetFlags == MipsII::MO_ABS_HI)
lowerLongBranchADDiu(MI, OutMI, Mips::DADDiu,
MCSymbolRefExpr::VK_Mips_ABS_HI);
else if (TargetFlags == MipsII::MO_ABS_LO)

3
lib/Target/Mips/MipsMCInstLower.h
View File

@ -39,8 +39,7 @@ private:
MachineOperandType MOTy, unsigned Offset) const;
MCOperand createSub(MachineBasicBlock *BB1, MachineBasicBlock *BB2,
MCSymbolRefExpr::VariantKind Kind) const;
void lowerLongBranchLUi(const MachineInstr *MI, MCInst &OutMI,
int Opcode, MCSymbolRefExpr::VariantKind Kind) const;
void lowerLongBranchLUi(const MachineInstr *MI, MCInst &OutMI) const;
void lowerLongBranchADDiu(const MachineInstr *MI, MCInst &OutMI,
int Opcode,
MCSymbolRefExpr::VariantKind Kind) const;

5
test/CodeGen/Mips/longbranch.ll
View File

@ -80,10 +80,7 @@ end:
; Check for long branch expansion:
; N64: daddiu $sp, $sp, -16
; N64-NEXT: sd $ra, 0($sp)
; N64-NEXT: lui $1, %highest(($[[BB2:BB[0-9_]+]])-($[[BB1:BB[0-9_]+]]))
; N64-NEXT: daddiu $1, $1, %higher(($[[BB2]])-($[[BB1]]))
; N64-NEXT: dsll $1, $1, 16
; N64-NEXT: daddiu $1, $1, %hi(($[[BB2]])-($[[BB1]]))
; N64-NEXT: daddiu $1, $zero, %hi(($[[BB2:BB[0-9_]+]])-($[[BB1:BB[0-9_]+]]))
; N64-NEXT: dsll $1, $1, 16
; N64-NEXT: bal $[[BB1]]
; N64-NEXT: daddiu $1, $1, %lo(($[[BB2]])-($[[BB1]]))