AArch64CondBrTuning.cpp File Reference

This file contains a pass that transforms CBZ/CBNZ/TBZ/TBNZ instructions into a conditional branch (B.cond), when the NZCV flags can be set for "free". More...

#include "AArch64.h"
#include "AArch64Subtarget.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"

Include dependency graph for AArch64CondBrTuning.cpp:

Go to the source code of this file.

Macros
#define	DEBUG_TYPE   "aarch64-cond-br-tuning"
#define	AARCH64_CONDBR_TUNING_NAME   "AArch64 Conditional Branch Tuning"

Functions
	INITIALIZE_PASS (AArch64CondBrTuning, "aarch64-cond-br-tuning", AARCH64_CONDBR_TUNING_NAME, false, false) void AArch64CondBrTuning

Detailed Description

This file contains a pass that transforms CBZ/CBNZ/TBZ/TBNZ instructions into a conditional branch (B.cond), when the NZCV flags can be set for "free".

This is preferred on targets that have more flexibility when scheduling B.cond instructions as compared to CBZ/CBNZ/TBZ/TBNZ (assuming all other variables are equal). This can also reduce register pressure.

A few examples:

1) add w8, w0, w1 -> cmn w0, w1 ; CMN is an alias of ADDS. cbz w8, .LBB_2 -> b.eq .LBB0_2

2) add w8, w0, w1 -> adds w8, w0, w1 ; w8 has multiple uses. cbz w8, .LBB1_2 -> b.eq .LBB1_2

3) sub w8, w0, w1 -> subs w8, w0, w1 ; w8 has multiple uses. tbz w8, #31, .LBB6_2 -> b.pl .LBB6_2

Definition in file AArch64CondBrTuning.cpp.

Macro Definition Documentation

AARCH64_CONDBR_TUNING_NAME

#define AARCH64_CONDBR_TUNING_NAME   "AArch64 Conditional Branch Tuning"

Definition at line 45 of file AArch64CondBrTuning.cpp.

DEBUG_TYPE

#define DEBUG_TYPE   "aarch64-cond-br-tuning"

Definition at line 44 of file AArch64CondBrTuning.cpp.

Function Documentation

INITIALIZE_PASS()

INITIALIZE_PASS	(	AArch64CondBrTuning	,
		"aarch64-cond-br-tuning"	,
		AARCH64_CONDBR_TUNING_NAME	,
		false	,
		false
	)

Definition at line 73 of file AArch64CondBrTuning.cpp.

References llvm::MachineInstrBuilder::add(), llvm::MachineInstrBuilder::addMBB(), assert(), llvm::BuildMI(), llvm::dbgs(), DefMI, E, llvm::AArch64CC::EQ, llvm::MachineInstr::eraseFromParent(), llvm::MachineFunctionPass::getAnalysisUsage(), llvm::MachineInstr::getDebugLoc(), llvm::MachineFunction::getFunction(), llvm::MachineOperand::getImm(), llvm::TargetSubtargetInfo::getInstrInfo(), llvm::MachineFunction::getName(), llvm::MachineInstr::getNumExplicitOperands(), llvm::MachineInstr::getNumOperands(), llvm::MachineInstr::getOpcode(), llvm::MachineInstr::getOperand(), llvm::MachineInstr::getParent(), llvm::MachineOperand::getReg(), llvm::MachineFunction::getRegInfo(), llvm::TargetSubtargetInfo::getRegisterInfo(), llvm::MachineFunction::getSubtarget(), I, llvm::MachineOperand::isDead(), llvm::MachineOperand::isReg(), llvm::TargetRegisterInfo::isVirtualRegister(), LLVM_DEBUG, LLVM_FALLTHROUGH, llvm_unreachable, MI, llvm::AArch64CC::MI, MRI, llvm::AArch64CC::NE, llvm::AArch64CC::PL, llvm::MachineInstr::print(), llvm::MachineOperand::setIsDead(), TII, and TRI.