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Commit e709a50

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Yonghong Song
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Handle jump table change in machine-sink pass
The implementation is similar to func getJumpTableIndex() in X86InstrInfo.cpp. For the following example: struct simple_ctx { int x; int y; int z; }; int ret_user, ret_user2; void bar(void); int foo(struct simple_ctx *ctx, struct simple_ctx *ctx2) { switch (ctx->x) { case 1: ret_user = 8; break; case 6: ret_user = 3; break; case 2: ret_user = 4; break; case 31: ret_user = 5; break; default: ret_user = 19; break; } bar(); switch (ctx2->x) { case 0: ret_user2 = 8; break; case 7: ret_user2 = 3; break; case 9: ret_user2 = 4; break; case 31: ret_user2 = 5; break; default: ret_user2 = 29; break; } return 0; } Before machine-sink pass, Jump Tables: %jump-table.0: %bb.5 %bb.2 %bb.4 %bb.4 %bb.4 %bb.1 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.3 %jump-table.1: %bb.10 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.6 %bb.9 %bb.7 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.8 Machine-level IR: bb.0.entry: successors: %bb.4(0x0ccccccb), %bb.11(0x73333335); %bb.4(10.00%), %bb.11(90.00%) liveins: $r1, $r2 %3:gpr = COPY $r2 %2:gpr = COPY $r1 %4:gpr32 = MOV_ri_32 8 %6:gpr32 = LDW32 %2:gpr, 0 :: (load (s32) from %ir.ctx, !tbaa !3) %7:gpr32 = ADD_ri_32 %6:gpr32(tied-def 0), -1 %5:gpr = MOV_32_64 %7:gpr32 JUGT_ri_32 %7:gpr32, 30, %bb.4 bb.11.entry: ; predecessors: %bb.0 successors: %bb.5(0x1c71c71c), %bb.2(0x1c71c71c), %bb.4(0x0e38e38e), %bb.1(0x1c71c71c), %bb.3(0x1c71c71c); %bb.5(22.22%), %bb.2(22.22%), %bb.4(11.11%), %bb.1(22.22%), %bb.3(22.22%) %8:gpr = SLL_ri %5:gpr(tied-def 0), 3 %9:gpr = LD_imm64 %jump-table.0 %10:gpr = ADD_rr %9:gpr(tied-def 0), killed %8:gpr %11:gpr = LDD killed %10:gpr, 0 :: (load (s64) from jump-table) JX killed %11:gpr bb.1.sw.bb1: ; predecessors: %bb.11 successors: %bb.5(0x80000000); %bb.5(100.00%) %14:gpr32 = MOV_ri_32 3 JMP %bb.5 bb.2.sw.bb2: ; predecessors: %bb.11 successors: %bb.5(0x80000000); %bb.5(100.00%) %13:gpr32 = MOV_ri_32 4 JMP %bb.5 bb.3.sw.bb3: ; predecessors: %bb.11 successors: %bb.5(0x80000000); %bb.5(100.00%) %12:gpr32 = MOV_ri_32 5 JMP %bb.5 bb.4.sw.default: ; predecessors: %bb.11, %bb.0 successors: %bb.5(0x80000000); %bb.5(100.00%) %15:gpr32 = MOV_ri_32 19 bb.5.sw.epilog: ... After machine-sink pass: Jump Tables: %jump-table.0: %bb.13 %bb.2 %bb.4 %bb.4 %bb.4 %bb.1 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.4 %bb.3 %jump-table.1: %bb.14 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.6 %bb.9 %bb.7 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.9 %bb.8 Machine-level IR: bb.0.entry: successors: %bb.4(0x0ccccccb), %bb.11(0x73333335); %bb.4(10.00%), %bb.11(90.00%) liveins: $r1, $r2 %3:gpr = COPY $r2 %2:gpr = COPY $r1 %6:gpr32 = LDW32 %2:gpr, 0 :: (load (s32) from %ir.ctx, !tbaa !3) %7:gpr32 = ADD_ri_32 %6:gpr32(tied-def 0), -1 JUGT_ri_32 %7:gpr32, 30, %bb.4 bb.11.entry: ; predecessors: %bb.0 successors: %bb.13(0x1c71c71c), %bb.2(0x1c71c71c), %bb.4(0x0e38e38e), %bb.1(0x1c71c71c), %bb.3(0x1c71c71c); %bb.13(22.22%), %bb.2(22.22%), %bb.4(11.11%), %bb.1(22.22%), %bb.3(22.22%) %5:gpr = MOV_32_64 %7:gpr32 %8:gpr = SLL_ri %5:gpr(tied-def 0), 3 %9:gpr = LD_imm64 %jump-table.0 %10:gpr = ADD_rr %9:gpr(tied-def 0), killed %8:gpr %11:gpr = LDD killed %10:gpr, 0 :: (load (s64) from jump-table) JX killed %11:gpr bb.13: ; predecessors: %bb.11 successors: %bb.5(0x80000000); %bb.5(100.00%) %4:gpr32 = MOV_ri_32 8 JMP %bb.5 bb.1.sw.bb1: ; predecessors: %bb.11 successors: %bb.5(0x80000000); %bb.5(100.00%) %14:gpr32 = MOV_ri_32 3 JMP %bb.5 bb.2.sw.bb2: ; predecessors: %bb.11 successors: %bb.5(0x80000000); %bb.5(100.00%) %13:gpr32 = MOV_ri_32 4 JMP %bb.5 bb.3.sw.bb3: ; predecessors: %bb.11 successors: %bb.5(0x80000000); %bb.5(100.00%) %12:gpr32 = MOV_ri_32 5 JMP %bb.5 bb.4.sw.default: ; predecessors: %bb.11, %bb.0 successors: %bb.5(0x80000000); %bb.5(100.00%) %15:gpr32 = MOV_ri_32 19 bb.5.sw.epilog: Before machine-sink pass, '%4:gpr32 = MOV_ri_32 8' is in the entry block so there is no switch-branch for value 8. But machine-sink pass later removed '%4:gpr32 = MOV_ri_32 8' and add back the switch-branch with value 8. Such transformation requires adjust the jump table. This commit implemented backend callback function getJumpTableIndex() so jump table can be properly updated.
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‎llvm/lib/Target/BPF/BPFInstrInfo.cpp

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Original file line numberDiff line numberDiff line change
@@ -263,3 +263,40 @@ unsigned BPFInstrInfo::removeBranch(MachineBasicBlock &MBB,
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return Count;
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}
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int BPFInstrInfo::getJumpTableIndex(const MachineInstr &MI) const {
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// The pattern looks like:
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// %0 = LD_imm64 %jump-table.0 ; load jump-table address
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// %1 = ADD_rr %0, $another_reg ; address + offset
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// %2 = LDD %1, 0 ; load the actual label
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// JX %2
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const MachineFunction &MF = *MI.getParent()->getParent();
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const MachineRegisterInfo &MRI = MF.getRegInfo();
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Register Reg = MI.getOperand(0).getReg();
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if (!Reg.isVirtual())
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return -1;
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MachineInstr *Ldd = MRI.getUniqueVRegDef(Reg);
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if (Ldd == nullptr || Ldd->getOpcode() != BPF::LDD)
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return -1;
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Reg = Ldd->getOperand(1).getReg();
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if (!Reg.isVirtual())
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return -1;
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MachineInstr *Add = MRI.getUniqueVRegDef(Reg);
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if (Add == nullptr || Add->getOpcode() != BPF::ADD_rr)
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return -1;
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Reg = Add->getOperand(1).getReg();
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if (!Reg.isVirtual())
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return -1;
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MachineInstr *LDimm64 = MRI.getUniqueVRegDef(Reg);
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if (LDimm64 == nullptr || LDimm64->getOpcode() != BPF::LD_imm64)
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return -1;
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const MachineOperand &MO = LDimm64->getOperand(1);
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if (!MO.isJTI())
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return -1;
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return MO.getIndex();
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}

‎llvm/lib/Target/BPF/BPFInstrInfo.h

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -58,6 +58,9 @@ class BPFInstrInfo : public BPFGenInstrInfo {
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MachineBasicBlock *FBB, ArrayRef<MachineOperand> Cond,
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const DebugLoc &DL,
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int *BytesAdded = nullptr) const override;
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int getJumpTableIndex(const MachineInstr &MI) const override;
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private:
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void expandMEMCPY(MachineBasicBlock::iterator) const;
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