Index: llvm/lib/CodeGen/DeadMachineInstructionElim.cpp =================================================================== --- llvm/lib/CodeGen/DeadMachineInstructionElim.cpp +++ llvm/lib/CodeGen/DeadMachineInstructionElim.cpp @@ -10,6 +10,7 @@ // //===----------------------------------------------------------------------===// +#include "llvm/ADT/PostOrderIterator.h" #include "llvm/ADT/Statistic.h" #include "llvm/CodeGen/MachineFunctionPass.h" #include "llvm/CodeGen/MachineRegisterInfo.h" @@ -48,6 +49,8 @@ private: bool isDead(const MachineInstr *MI) const; + + bool eliminateDeadMI(MachineFunction &MF); }; } char DeadMachineInstructionElim::ID = 0; @@ -107,7 +110,13 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) { if (skipFunction(MF.getFunction())) return false; + bool AnyChanges = eliminateDeadMI(MF); + while (AnyChanges && eliminateDeadMI(MF)) + ; + return AnyChanges; +} +bool DeadMachineInstructionElim::eliminateDeadMI(MachineFunction &MF) { bool AnyChanges = false; MRI = &MF.getRegInfo(); TRI = MF.getSubtarget().getRegisterInfo(); @@ -116,22 +125,22 @@ // Loop over all instructions in all blocks, from bottom to top, so that it's // more likely that chains of dependent but ultimately dead instructions will // be cleaned up. - for (MachineBasicBlock &MBB : make_range(MF.rbegin(), MF.rend())) { + for (MachineBasicBlock *MBB : post_order(&MF)) { // Start out assuming that reserved registers are live out of this block. LivePhysRegs = MRI->getReservedRegs(); // Add live-ins from successors to LivePhysRegs. Normally, physregs are not // live across blocks, but some targets (x86) can have flags live out of a // block. - for (MachineBasicBlock::succ_iterator S = MBB.succ_begin(), - E = MBB.succ_end(); S != E; S++) + for (MachineBasicBlock::succ_iterator S = MBB->succ_begin(), + E = MBB->succ_end(); S != E; S++) for (const auto &LI : (*S)->liveins()) LivePhysRegs.set(LI.PhysReg); // Now scan the instructions and delete dead ones, tracking physreg // liveness as we go. - for (MachineBasicBlock::reverse_iterator MII = MBB.rbegin(), - MIE = MBB.rend(); MII != MIE; ) { + for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(), + MIE = MBB->rend(); MII != MIE;) { MachineInstr *MI = &*MII++; // If the instruction is dead, delete it! Index: llvm/test/CodeGen/AArch64/elim-dead-mi.mir =================================================================== --- /dev/null +++ llvm/test/CodeGen/AArch64/elim-dead-mi.mir @@ -0,0 +1,61 @@ +# RUN: llc -mtriple=aarch64-arm-none-eabi -o - %s \ +# RUN: -run-pass dead-mi-elimination | FileCheck %s +--- | + @c = internal unnamed_addr global [3 x i8] zeroinitializer, align 4 + @d = common dso_local local_unnamed_addr global i32 0, align 4 + + define dso_local i32 @main() local_unnamed_addr { + %scevgep = getelementptr i8, i8* getelementptr inbounds ([3 x i8], [3 x i8]* @c, i64 0, i64 1), i64 0 + ret i32 0 + } +... +--- +name: main +tracksRegLiveness: true +registers: + - { id: 0, class: gpr64, preferred-register: '' } + - { id: 1, class: gpr64common, preferred-register: '' } + - { id: 2, class: gpr64, preferred-register: '' } + - { id: 3, class: gpr64common, preferred-register: '' } + - { id: 4, class: gpr32, preferred-register: '' } + - { id: 5, class: gpr32all, preferred-register: '' } + - { id: 6, class: gpr64, preferred-register: '' } +body: | + bb.0: + successors: %bb.4(0x30000000), %bb.5(0x50000000) + + %0:gpr64 = MOVaddr target-flags(aarch64-page) @c, target-flags(aarch64-pageoff, aarch64-nc) @c + CBZX killed %0, %bb.4 + B %bb.5 + + bb.1: + successors: %bb.3(0x04000000), %bb.2(0x7c000000) + + %1:gpr64common = MOVaddr target-flags(aarch64-page) @c, target-flags(aarch64-pageoff, aarch64-nc) @c + %2:gpr64 = SUBSXri %1, 2, 0, implicit-def $nzcv + Bcc 0, %bb.3, implicit $nzcv + B %bb.2 + + bb.2: + successors: %bb.1(0x80000000) + %3:gpr64common = ADDXrr %6, %2 + %4:gpr32 = LDRBBui killed %3, 1 :: (load 1 from %ir.scevgep) + %5:gpr32all = COPY %4 + B %bb.1 + + bb.3: + ADJCALLSTACKDOWN 0, 0, implicit-def dead $sp, implicit $sp + $x0 = MOVaddr target-flags(aarch64-page) @c, target-flags(aarch64-pageoff, aarch64-nc) @c + ADJCALLSTACKUP 0, 0, implicit-def dead $sp, implicit $sp + RET_ReallyLR implicit $w0 + + bb.4: + successors: %bb.5(0x80000000) + + bb.5: + successors: %bb.1(0x80000000) + ; CHECK: bb.5 + ; CHECK-NOT: %6:gpr64 = MOVaddr target-flags(aarch64-page) @c, target-flags(aarch64-pageoff, aarch64-nc) @c + %6:gpr64 = MOVaddr target-flags(aarch64-page) @c, target-flags(aarch64-pageoff, aarch64-nc) @c + B %bb.1 +...