[llvm-dev] How to avoid multiple registers definitions in customInserter.

[Dominique Torette via llvm-dev]

Hi,

I'm lowering some of the logical operators (by example the | operator)  on integer32.
Sadly my target only provide native instruction on high and low parts of 32 bits registers.
So, I have to generate a sequence of two native instructions (LOR followed by HOR).
I've introduced an Pseudo instruction with a custom inserter.

def OR_A_oo             : CLPPseudoInst<(ins FPUaOffsetOperand:$OffsetA,FPUaOffsetOperand:$OffsetB),(outs FPUaROUTADDRegisterClass:$FA_ROUTADD),
                                                                [], [RFLAGA],
                                                                "# OR_A_oo",
                                                                [(set FPUaROUTADDRegisterClass:$FA_ROUTADD,(or  FPUaOffsetOperand:$OffsetA,FPUaOffsetOperand:$OffsetB))],NoItinerary>
                                                                {let usesCustomInserter = 1;}

The instructions selection and registers allocation are performed with the pseudo.

        %4:fpuaoffsetclass = LOAD_A_r @a; FPUaOffsetClass:%4
        %5:fpuaoffsetclass = LOAD_A_r @b; FPUaOffsetClass:%5
        %6:fpuaroutaddregisterclass = OR_A_oo killed %5, killed %4, implicit-def dead %rflaga; FPUaROUTADDRegisterClass:%6 FPUaOffsetClass:%5,%4
        %7:fpuaoffsetclass = COPY %6; FPUaOffsetClass:%7 FPUaROUTADDRegisterClass:%6
        MOV_A_or killed %7, @c1; FPUaOffsetClass:%7
        %8:fpuaoffsetclass = LOAD_A_r @c1; FPUaOffsetClass:%8

A virtual register %6 has been allocated for the out of the pseudo. So far, so good.

My customInserter (see below) is may be over simplistic.
After investigation on the code produce by my customInserter, I've noticed the following problems:
        1)      %6 seems to be defined twice
        2)      %5 is killed twice.

320B            MOV_A_ro @a, def %4; FPUaOffsetClass:%4
336B            MOV_A_ro @b, def %5; FPUaOffsetClass:%5
352B            %6:fpuaroutaddregisterclass = LOR_A_oo killed %5, implicit-def %rflaga; FPUaROUTADDRegisterClass:%6 FPUaOffsetClass:%5
368B            %6:fpuaroutaddregisterclass = HOR_A_oo killed %5, implicit-def %rflaga; FPUaROUTADDRegisterClass:%6 FPUaOffsetClass:%5
384B            %7:fpuaoffsetclass = COPY %6; FPUaOffsetClass:%7 FPUaROUTADDRegisterClass:%6
400B            MOV_A_or killed %7, @c1; FPUaOffsetClass:%7
416B            MOV_A_ro @c1, def %8; FPUaOffsetClass:%8

Result: an assertion is raised... !!

********** PROCESS IMPLICIT DEFS **********
********** Function: _start
llc: /home/dte/eclipse-workspace/llvm/lib/CodeGen/MachineRegisterInfo.cpp:366: llvm::MachineInstr* llvm::MachineRegisterInfo::getVRegDef(unsigned int) const: Assertion `(I.atEnd() || std::next(I) == def_instr_end()) && "getVRegDef assumes a single definition or no definition"' failed.
LLVMSymbolizer: error reading file: No such file or directory

Here is the inner part of my customInserter.
Are there any additional actions to perform during the customInserter.

MachineBasicBlock *
CLPTargetLowering::emitLOpcodeHOpcode(MachineInstr &MI,
        MachineBasicBlock *MBB,
                  unsigned LOpcode,
                  unsigned HOpcode) const {
        const TargetInstrInfo *TII = Subtarget->getInstrInfo();
        DebugLoc Loc = MI.getDebugLoc();

        const MachineOperand operand0 = MI.getOperand(0);
        const MachineOperand operand1 = MI.getOperand(1);

        BuildMI(*MBB, MI, Loc, TII->get(LOpcode))
        .add(operand0)
        .add(operand1);
        BuildMI(*MBB, MI, Loc, TII->get(HOpcode))
        .add(operand0)
        .add(operand1);

        MI.eraseFromParent();

        return MBB;
}

Dominique Torette
System Architect
Rue des Chasseurs Ardennais - Liège Science Park - B-4031 Angleur
Tel: +32 (0) 4 361 81 11 - Fax: +32 (0) 4 361 81 20
www.spacebel.be





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