[GlobalISel] Only merge memory ops for mayLoad or mayStore instrs.

[fhahn]

Summary

We only need to merge memory operands for instructions that access
memory. This slightly reduces the number of actions executed.

[dsanders]

Limiting memory operands to instructions involving memory is a change I want to make but before we do that, could you elaborate a bit on the spurious memory operand you're seeing? In particular, was that memory operand present on any of the instructions covered by the match? I'm wondering if you've hit the bug that will be fixed by https://reviews.llvm.org/D36094.

[fhahn]

Yes, D36094 fixes the problem too! Here's what's going on in the test case, without any of the 2 patches:

Legalize Machine IR for: test_stack_args_i32
Legalizing: %vreg6<def>(p0) = G_FRAME_INDEX <fi#-1>;
.. Already legal
Legalizing: %vreg4<def>(s32) = G_LOAD %vreg6; mem:LD4[FixedStack-1](align=0)
.. Already legal
Legalizing: %vreg7<def>(p0) = G_FRAME_INDEX <fi#-2>;
.. Already legal
Legalizing: %vreg5<def>(s32) = G_LOAD %vreg7; mem:LD4[FixedStack-2](align=0)
.. Already legal
Legalizing: %vreg8<def>(s32) = G_ADD %vreg2, %vreg5;
.. Already legal

......

34378: Resume at 34378 (0 try-blocks remain)
34379: Begin try-block
34382: GIM_CheckFeatures(ExpectedBitsetID=5)
34385: GIM_CheckNumOperands(MIs[0], Expected=3)
34388: GIM_CheckOpcode(MIs[0], ExpectedOpcode=30) // Got=30
34392: GIM_CheckType(MIs[0]->getOperand(0), TypeID=21)
34396: GIM_CheckRegBankForClass(MIs[0]->getOperand(0), RCEnum=1)
34400: GIM_CheckType(MIs[0]->getOperand(1), TypeID=21)
34404: GIM_CheckRegBankForClass(MIs[0]->getOperand(1), RCEnum=1)
34408: GIM_CheckType(MIs[0]->getOperand(2), TypeID=21)
34412: GIM_CheckRegBankForClass(MIs[0]->getOperand(2), RCEnum=1)
34415: GIR_BuildMI(OutMIs[0], 112)
34419: GIR_Copy(OutMIs[0], MIs[0], 0)
34423: GIR_Copy(OutMIs[0], MIs[0], 1)
34427: GIR_Copy(OutMIs[0], MIs[0], 2)
34430: GIR_AddImm(OutMIs[0], 14)
34433: GIR_AddRegister(OutMIs[0], 0)
34436: GIR_AddRegister(OutMIs[0], 0)
34438: GIR_MergeMemOperands(OutMIs[0])
34440: GIR_EraseFromParent(MIs[0])
Converting operand: %vreg8<def>
Converting operand: %vreg2
Converting operand: %vreg5
Converting operand: %noreg
Converting operand: %noreg
34442: GIR_ConstrainSelectedInstOperands(OutMIs[0])
34443: GIR_DoneInto:
  %vreg8<def>(s32) = ADDrr %vreg2, %vreg5, pred:14, pred:%noreg, opt:%noreg; mem:LD4[FixedStack-2](align=0) GPR:%vreg8,%vreg2,%vreg5

With the MachineVerifier enabled for ARM, this causes it to fail on the test case.

Would it still make sense to only emit GIR_MergeMemOperands for instructions that mayLoad/mayStore? Unless I am missing something, I think not having this action when it's not required would speed up GlobalISel a tiny bit.

[dsanders]

In D36151#827515, @fhahn wrote:

Yes, D36094 fixes the problem too! Here's what's going on in the test case, without any of the 2 patches:

Great! In that case I'll update the summary of that patch to indicate that arm-isel.ll shows the same problem in-tree.

Would it still make sense to only emit GIR_MergeMemOperands for instructions that mayLoad/mayStore? Unless I am missing something, I think not having this action when it's not required would speed up GlobalISel a tiny bit.

Yes, it does. As you say, not using GIR_MergeMemOperands unnecessarily will speed up the matcher. It will also become important later on when load/store is importable and we support multi-instruction emission since something will have to ensure the memory operands are added to appropriate instructions.

This patch LGTM. Ideally, D36094 would land first since that fixes the underlying problem but that hasn't been reviewed yet and I see no reason to require that it lands first.

[fhahn]

Rebased

test/TableGen/GlobalISelEmitter.td

 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/3, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckComplexPattern, /*MI*/0, /*Op*/3, /*Renderer*/1, GICP_gi_complex,
 // CHECK-NEXT:    // (select:i32 GPR32:i32:$src1, complex:i32:$src2, complex:i32:$src3) => (INSN2:i32 GPR32:i32:$src1, complex:i32:$src3, complex:i32:$src2)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::INSN2,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src1
 // CHECK-NEXT:    GIR_ComplexRenderer, /*InsnID*/0, /*RendererID*/1,
 // CHECK-NEXT:    GIR_ComplexRenderer, /*InsnID*/0, /*RendererID*/0,
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
-// CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
+// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList, GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 0: @[[LABEL]]
 
 def INSN3 : I<(outs GPR32:$dst),
               (ins GPR32Op:$src1, complex:$src2, GPR32:$src3, complex:$src4, complex:$src5), []>;
 def : Pat<(select GPR32:$src1, complex:$src2, (select GPR32:$src3, complex:$src4, complex:$src5)),
           (INSN3 GPR32:$src1, complex:$src2, GPR32:$src3, complex:$src4, complex:$src5)>;

 // CHECK-NEXT:    // (select:i32 GPR32:i32:$src1, complex:i32:$src2, (select:i32 GPR32:i32:$src3, complex:i32:$src4, complex:i32:$src5))  =>  (INSN3:i32 GPR32:i32:$src1, complex:i32:$src2, GPR32:i32:$src3, complex:i32:$src4, complex:i32:$src5)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::INSN3,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src1
 // CHECK-NEXT:    GIR_ComplexRenderer, /*InsnID*/0, /*RendererID*/0,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/1, /*OpIdx*/1, // src3
 // CHECK-NEXT:    GIR_ComplexRenderer, /*InsnID*/0, /*RendererID*/1,
 // CHECK-NEXT:    GIR_ComplexRenderer, /*InsnID*/0, /*RendererID*/2,
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, 1, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 1: @[[LABEL]]
 
 def : GINodeEquiv<G_SELECT, select>;
+let mayLoad = 1 in {
   def INSN2 : I<(outs GPR32:$dst), (ins GPR32Op:$src1, complex:$src2, complex:$src3), []>;
+}
 def : Pat<(select GPR32:$src1, complex:$src2, complex:$src3),
           (INSN2 GPR32:$src1, complex:$src3, complex:$src2)>;
 
 //===- Test a simple pattern with regclass operands. ----------------------===//
 
 // CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 2*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_ADD,

 // CHECK-NEXT:    // MIs[0] src1
 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/2, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckRegBankForClass, /*MI*/0, /*Op*/2, /*RC*/MyTarget::GPR32RegClassID,
 // CHECK-NEXT:    // (intrinsic_wo_chain:i32 [[ID:[0-9]+]]:iPTR, GPR32:i32:$src1) => (MOV:i32 GPR32:i32:$src1)
 
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::MOV,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/2, // src1
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 3: @[[LABEL]]
 
 def MOV : I<(outs GPR32:$dst), (ins GPR32:$src1),
             [(set GPR32:$dst, (int_mytarget_nop GPR32:$src1))]>;
 

 // CHECK-NEXT:    GIM_CheckRegBankForClass, /*MI*/0, /*Op*/2, /*RC*/MyTarget::GPR32RegClassID,
 // CHECK-NEXT:    GIM_CheckIsSafeToFold, /*InsnID*/1,
 // CHECK-NEXT:    // (mul:i32 (add:i32 GPR32:i32:$src1, GPR32:i32:$src2), GPR32:i32:$src3)  =>  (MULADD:i32 GPR32:i32:$src1, GPR32:i32:$src2, GPR32:i32:$src3)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::MULADD,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/1, /*OpIdx*/1, // src1
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/1, /*OpIdx*/2, // src2
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/2, // src3
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, 1, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 4: @[[LABEL]]
 
 // We also get a second rule by commutativity.
 // CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 5*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckFeatures, GIFBS_HasA,

 // CHECK-NEXT:    GIM_CheckRegBankForClass, /*MI*/1, /*Op*/2, /*RC*/MyTarget::GPR32RegClassID,
 // CHECK-NEXT:    GIM_CheckIsSafeToFold, /*InsnID*/1,
 // CHECK-NEXT:    // (mul:i32 GPR32:i32:$src3, (add:i32 GPR32:i32:$src1, GPR32:i32:$src2))  =>  (MULADD:i32 GPR32:i32:$src1, GPR32:i32:$src2, GPR32:i32:$src3)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::MULADD,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/1, /*OpIdx*/1, // src1
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/1, /*OpIdx*/2, // src2
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src3
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, 1, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 5: @[[LABEL]]
 
 def MULADD : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3),
                [(set GPR32:$dst,
                      (mul (add GPR32:$src1, GPR32:$src2), GPR32:$src3))]>,

 // CHECK-NEXT:    // MIs[0] src2
 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/2, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckRegBankForClass, /*MI*/0, /*Op*/2, /*RC*/MyTarget::GPR32RegClassID,
 // CHECK-NEXT:    // (mul:i32 GPR32:i32:$src1, GPR32:i32:$src2) => (MUL:i32 GPR32:i32:$src2, GPR32:i32:$src1)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::MUL,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/2, // src2
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src1
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 6: @[[LABEL]]
 
 def MUL : I<(outs GPR32:$dst), (ins GPR32:$src2, GPR32:$src1),
              [(set GPR32:$dst, (mul GPR32:$src1, GPR32:$src2))]>,
           Requires<[HasA, HasB, HasC]>;

 // CHECK-NEXT:    GIM_CheckIsSafeToFold, /*InsnID*/2,
 // CHECK-NEXT:    // (sub:i32 (sub:i32 GPR32:i32:$src1, GPR32:i32:$src2), (sub:i32 GPR32:i32:$src3, GPR32:i32:$src4)) => (INSNBOB:i32 GPR32:i32:$src1, GPR32:i32:$src2, GPR32:i32:$src3, GPR32:i32:$src4)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::INSNBOB,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/1, /*OpIdx*/1, // src1
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/1, /*OpIdx*/2, // src2
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/2, /*OpIdx*/1, // src3
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/2, /*OpIdx*/2, // src4
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, 1, 2, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 7: @[[LABEL]]
 
 def INSNBOB : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3, GPR32:$src4),
                  [(set GPR32:$dst,
                       (sub (sub GPR32:$src1, GPR32:$src2), (sub GPR32:$src3, GPR32:$src4)))]>,

 // CHECK-NEXT:    // MIs[0] src2
 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/2, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckComplexPattern, /*MI*/0, /*Op*/2, /*Renderer*/0, GICP_gi_complex,
 // CHECK-NEXT:    // (sub:i32 GPR32:i32:$src1, complex:i32:$src2) => (INSN1:i32 GPR32:i32:$src1, complex:i32:$src2)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::INSN1,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src1
 // CHECK-NEXT:    GIR_ComplexRenderer, /*InsnID*/0, /*RendererID*/0,
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 8: @[[LABEL]]
 
 def INSN1 : I<(outs GPR32:$dst), (ins GPR32:$src1, complex:$src2), []>;
 def : Pat<(sub GPR32:$src1, complex:$src2), (INSN1 GPR32:$src1, complex:$src2)>;
 

 // CHECK-NEXT:    // MIs[0] Operand 2
 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/2, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckConstantInt, /*MI*/0, /*Op*/2, -2
 // CHECK-NEXT:    // (xor:i32 GPR32:i32:$src1, -2:i32) => (XORI:i32 GPR32:i32:$src1)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::XORI,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_AddImm, /*InsnID*/0, /*Imm*/-1,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src1
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 9: @[[LABEL]]
 
 // The -2 is just to distinguish it from the 'not' case below.
 def XORI : I<(outs GPR32:$dst), (ins m1:$src2, GPR32:$src1),
              [(set GPR32:$dst, (xor GPR32:$src1, -2))]>;

 // CHECK-NEXT:    // MIs[0] Operand 2
 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/2, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckConstantInt, /*MI*/0, /*Op*/2, -3
 // CHECK-NEXT:    // (xor:i32 GPR32:i32:$src1, -3:i32) => (XOR:i32 GPR32:i32:$src1)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::XOR,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_AddRegister, /*InsnID*/0, MyTarget::R0,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src1
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 10: @[[LABEL]]
 
 // The -3 is just to distinguish it from the 'not' case below and the other default op case above.
 def XOR : I<(outs GPR32:$dst), (ins Z:$src2, GPR32:$src1),
             [(set GPR32:$dst, (xor GPR32:$src1, -3))]>;

 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/2, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckConstantInt, /*MI*/0, /*Op*/2, -4
 // CHECK-NEXT:    // (xor:i32 GPR32:i32:$src1, -4:i32) => (XORlike:i32 GPR32:i32:$src1)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::XORlike,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_AddImm, /*InsnID*/0, /*Imm*/-1,
 // CHECK-NEXT:    GIR_AddRegister, /*InsnID*/0, MyTarget::R0,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src1
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 11: @[[LABEL]]
 
 // The -4 is just to distinguish it from the other 'not' cases.
 def XORlike : I<(outs GPR32:$dst), (ins m1Z:$src2, GPR32:$src1),
                 [(set GPR32:$dst, (xor GPR32:$src1, -4))]>;

 // CHECK-NEXT:    GIM_CheckConstantInt, /*MI*/0, /*Op*/2, -5,
 // CHECK-NEXT:    // (xor:i32 GPR32:i32:$src1, -5:i32) => (XORManyDefaults:i32 GPR32:i32:$src1)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::XORManyDefaults,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_AddImm, /*InsnID*/0, /*Imm*/-1,
 // CHECK-NEXT:    GIR_AddRegister, /*InsnID*/0, MyTarget::R0,
 // CHECK-NEXT:    GIR_AddRegister, /*InsnID*/0, MyTarget::R0,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src1
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 12: @[[LABEL]]
 
 // The -5 is just to distinguish it from the other cases.
 def XORManyDefaults : I<(outs GPR32:$dst), (ins m1Z:$src3, Z:$src2, GPR32:$src1),
                         [(set GPR32:$dst, (xor GPR32:$src1, -5))]>;

 // CHECK-NEXT:    // MIs[0] Operand 2
 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/2, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckConstantInt, /*MI*/0, /*Op*/2, -1,
 // CHECK-NEXT:    // (xor:i32 GPR32:i32:$Wm, -1:i32) => (ORN:i32 R0:i32, GPR32:i32:$Wm)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::ORN,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
 // CHECK-NEXT:    GIR_AddRegister, /*InsnID*/0, MyTarget::R0,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // Wm
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 13: @[[LABEL]]
 
 def ORN : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2), []>;
 def : Pat<(not GPR32:$Wm), (ORN R0, GPR32:$Wm)>;
 

 // CHECK-NEXT:    // MIs[0] dst
 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/0, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckRegBankForClass, /*MI*/0, /*Op*/0, /*RC*/MyTarget::GPR32RegClassID,
 // CHECK-NEXT:    // MIs[0] Operand 1
 // CHECK-NEXT:    GIM_CheckLiteralInt, /*MI*/0, /*Op*/1, 1,
 // CHECK-NEXT:    // 1:i32  =>  (MOV1:i32)
 // CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::MOV1,
 // CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
-// CHECK-NEXT:    GIR_MergeMemOperands, /*InsnID*/0, /*MergeInsnID's*/0, GIU_MergeMemOperands_EndOfList,
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
 // CHECK-NEXT:  // Label 15: @[[LABEL]]
 
 def MOV1 : I<(outs GPR32:$dst), (ins), [(set GPR32:$dst, 1)]>;
 
 //===- Test a pattern with an MBB operand. --------------------------------===//

utils/TableGen/GlobalISelEmitter.cpp

void emitActionOpcodes(MatchTable &Table, RuleMatcher &Rule,
 
     Table << MatchTable::Opcode("GIR_BuildMI") << MatchTable::Comment("InsnID")
           << MatchTable::IntValue(InsnID) << MatchTable::Comment("Opcode")
           << MatchTable::NamedValue(I->Namespace, I->TheDef->getName())
           << MatchTable::LineBreak;
     for (const auto &Renderer : OperandRenderers)
       Renderer->emitRenderOpcodes(Table, Rule);
 
+    if (I->mayLoad || I->mayStore) {
       Table << MatchTable::Opcode("GIR_MergeMemOperands")
             << MatchTable::Comment("InsnID") << MatchTable::IntValue(InsnID)
             << MatchTable::Comment("MergeInsnID's");
       // Emit the ID's for all the instructions that are matched by this rule.
       // TODO: Limit this to matched instructions that mayLoad/mayStore or have
-    //       some other means of having a memoperand. Also limit this to emitted
-    //       instructions that expect to have a memoperand too. For example,
-    //       (G_SEXT (G_LOAD x)) that results in separate load and sign-extend
-    //       instructions shouldn't put the memoperand on the sign-extend since
-    //       it has no effect there.
+      //       some other means of having a memoperand. Also limit this to
+      //       emitted instructions that expect to have a memoperand too. For
+      //       example, (G_SEXT (G_LOAD x)) that results in separate load and
+      //       sign-extend instructions shouldn't put the memoperand on the
+      //       sign-extend since it has no effect there.
       std::vector<unsigned> MergeInsnIDs;
       for (const auto &IDMatcherPair : Rule.defined_insn_vars())
         MergeInsnIDs.push_back(IDMatcherPair.second);
       std::sort(MergeInsnIDs.begin(), MergeInsnIDs.end());
       for (const auto &MergeInsnID : MergeInsnIDs)
         Table << MatchTable::IntValue(MergeInsnID);
-    Table << MatchTable::NamedValue("GIU_MergeMemOperands_EndOfList")
-          << MatchTable::LineBreak << MatchTable::Opcode("GIR_EraseFromParent")
+      Table << MatchTable::NamedValue("GIU_MergeMemOperands_EndOfList");
+    }
+
+    Table << MatchTable::Opcode("GIR_EraseFromParent")
           << MatchTable::Comment("InsnID")
           << MatchTable::IntValue(RecycleInsnID) << MatchTable::LineBreak;
   }
 };
 
 /// Generates code to constrain the operands of an output instruction to the
 /// register classes specified by the definition of that instruction.
 class ConstrainOperandsToDefinitionAction : public MatchAction {