[globalisel][tablegen] Simplify named operand/operator lookups and fix a wrong-code bug this revealed.

Summary: Operand variable lookups are now performed by the RuleMatcher rather than searching the whole matcher hierarchy for a match. This revealed a wrong-code bug that currently affects ARM and X86 where patterns that use a variable more than once in the match pattern will be imported but won't check that the operands are identical. This can cause the tablegen-erated matcher to accept matches that should be rejected. Depends on D36569 Reviewers: ab, t.p.northover, qcolombet, rovka, aditya_nandakumar Subscribers: aemerson, igorb, llvm-commits, kristof.beyls Differential Revision: https://reviews.llvm.org/D36618 llvm-svn: 315780
2024-11-23 03:02:36 +01:00 · 2017-10-14 00:31:58 +00:00 · 2017-10-14 00:31:58 +00:00 · d400a290e5
commit d400a290e5
parent efdd00d795
5 changed files with 274 additions and 108 deletions
--- a/include/llvm/CodeGen/GlobalISel/InstructionSelector.h
+++ b/include/llvm/CodeGen/GlobalISel/InstructionSelector.h
@ -150,6 +150,13 @@ enum {
  /// - InsnID - Instruction ID
  GIM_CheckIsSafeToFold,

+  /// Check the specified operands are identical.
+  /// - InsnID - Instruction ID
+  /// - OpIdx - Operand index
+  /// - OtherInsnID - Other instruction ID
+  /// - OtherOpIdx - Other operand index
+  GIM_CheckIsSameOperand,
+
  /// Fail the current try-block, or completely fail to match if there is no
  /// current try-block.
  GIM_Reject,
--- a/include/llvm/CodeGen/GlobalISel/InstructionSelectorImpl.h
+++ b/include/llvm/CodeGen/GlobalISel/InstructionSelectorImpl.h
@ -334,7 +334,25 @@ bool InstructionSelector::executeMatchTable(
      }
      break;
    }
-
+    case GIM_CheckIsSameOperand: {
+      int64_t InsnID = MatchTable[CurrentIdx++];
+      int64_t OpIdx = MatchTable[CurrentIdx++];
+      int64_t OtherInsnID = MatchTable[CurrentIdx++];
+      int64_t OtherOpIdx = MatchTable[CurrentIdx++];
+      DEBUG(dbgs() << CurrentIdx << ": GIM_CheckIsSameOperand(MIs[" << InsnID
+                   << "][" << OpIdx << "], MIs[" << OtherInsnID << "]["
+                   << OtherOpIdx << "])\n");
+      assert(State.MIs[InsnID] != nullptr && "Used insn before defined");
+      assert(State.MIs[OtherInsnID] != nullptr && "Used insn before defined");
+      State.MIs[InsnID]->getOperand(OpIdx).dump();
+      State.MIs[OtherInsnID]->getOperand(OtherOpIdx).dump();
+      if (!State.MIs[InsnID]->getOperand(OpIdx).isIdenticalTo(
+              State.MIs[OtherInsnID]->getOperand(OtherInsnID))) {
+        if (handleReject() == RejectAndGiveUp)
+          return false;
+      }
+      break;
+    }
    case GIM_Reject:
      DEBUG(dbgs() << CurrentIdx << ": GIM_Reject");
      if (handleReject() == RejectAndGiveUp)
--- a/test/CodeGen/X86/GlobalISel/select-blsr.mir
+++ b/test/CodeGen/X86/GlobalISel/select-blsr.mir
@ -0,0 +1,58 @@
+# RUN: llc -mtriple=x86_64-linux-gnu -mattr=+bmi -global-isel -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck %s
+#
+# Test that rules where multiple operands must be the same operand successfully
+# match. Also test that the rules do not match when they're not the same
+# operand.
+
+---
+name:            test_blsr32rr
+# CHECK-LABEL: name:  test_blsr32rr
+alignment:       4
+legalized:       true
+regBankSelected: true
+# CHECK:       registers:
+# CHECK-NEXT:     - { id: 0, class: gr32, preferred-register: '' }
+# CHECK-NEXT:     - { id: 1, class: gpr, preferred-register: '' }
+# CHECK-NEXT:     - { id: 2, class: gpr, preferred-register: '' }
+# CHECK-NEXT:     - { id: 3, class: gr32, preferred-register: '' }
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+  - { id: 2, class: gpr }
+  - { id: 3, class: gpr }
+# G_ADD and G_AND both use %0 so we should match this.
+# CHECK: %3 = BLSR32rr %0
+body:             |
+  bb.1:
+    liveins: %edi
+
+    %0(s32) = COPY %edi
+    %1(s32) = G_CONSTANT i32 -1
+    %2(s32) = G_ADD %0, %1
+    %3(s32) = G_AND %2, %0
+    %edi = COPY %3
+
+...
+---
+name:            test_blsr32rr_nomatch
+# CHECK-LABEL: name:  test_blsr32rr_nomatch
+alignment:       4
+legalized:       true
+regBankSelected: true
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+  - { id: 2, class: gpr }
+  - { id: 3, class: gpr }
+# G_ADD and G_AND use different operands so we shouldn't match this.
+# CHECK-NOT: BLSR32rr
+body:             |
+  bb.1:
+    liveins: %edi
+
+    %0(s32) = COPY %edi
+    %1(s32) = G_CONSTANT i32 -1
+    %2(s32) = G_ADD %1, %1
+    %3(s32) = G_AND %2, %0
+    %edi = COPY %3
+...
--- a/test/TableGen/GlobalISelEmitter.td
+++ b/test/TableGen/GlobalISelEmitter.td
@ -259,7 +259,7 @@ def : Pat<(select GPR32:$src1, complex:$src2, complex:$src3),
 def ADD : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2),
            [(set GPR32:$dst, (add GPR32:$src1, GPR32:$src2))]>;

-//===- Test a simple pattern with ValueType operands. ----------------------===//
+//===- Test a pattern with a tied operand in the matcher ------------------===//

 // CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 3*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
@ -267,6 +267,30 @@ def ADD : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2),
 // CHECK-NEXT:    // MIs[0] dst
 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/0, /*Type*/GILLT_s32,
 // CHECK-NEXT:    GIM_CheckRegBankForClass, /*MI*/0, /*Op*/0, /*RC*/MyTarget::GPR32RegClassID,
+// CHECK-NEXT:    // MIs[0] src{{$}}
+// CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/1, /*Type*/GILLT_s32,
+// CHECK-NEXT:    GIM_CheckRegBankForClass, /*MI*/0, /*Op*/1, /*RC*/MyTarget::GPR32RegClassID,
+// CHECK-NEXT:    // MIs[0] src{{$}}
+// CHECK-NEXT:    GIM_CheckIsSameOperand, /*MI*/0, /*OpIdx*/2, /*OtherMI*/0, /*OtherOpIdx*/1,
+// CHECK-NEXT:    // (add:{ *:[i32] } GPR32:{ *:[i32] }:$src, GPR32:{ *:[i32] }:$src) => (DOUBLE:{ *:[i32] } GPR32:{ *:[i32] }:$src)
+// CHECK-NEXT:    GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::DOUBLE,
+// CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/0, // dst
+// CHECK-NEXT:    GIR_Copy, /*NewInsnID*/0, /*OldInsnID*/0, /*OpIdx*/1, // src
+// CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
+// CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
+// CHECK-NEXT:    GIR_Done,
+// CHECK-NEXT:  // Label 3: @[[LABEL]]
+
+def DOUBLE : I<(outs GPR32:$dst), (ins GPR32:$src), [(set GPR32:$dst, (add GPR32:$src, GPR32:$src))]>;
+
+//===- Test a simple pattern with ValueType operands. ----------------------===//
+
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 4*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
+// CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_ADD,
+// CHECK-NEXT:    // MIs[0] dst
+// CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/0, /*Type*/GILLT_s32,
+// CHECK-NEXT:    GIM_CheckRegBankForClass, /*MI*/0, /*Op*/0, /*RC*/MyTarget::GPR32RegClassID,
 // CHECK-NEXT:    // MIs[0] src1
 // CHECK-NEXT:    GIM_CheckType, /*MI*/0, /*Op*/1, /*Type*/GILLT_s32,
 // CHECK-NEXT:    // MIs[0] src2
@ -275,7 +299,7 @@ def ADD : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2),
 // CHECK-NEXT:    GIR_MutateOpcode, /*InsnID*/0, /*RecycleInsnID*/0, /*Opcode*/MyTarget::ADD,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 3: @[[LABEL]]
+// CHECK-NEXT:  // Label 4: @[[LABEL]]

 def : Pat<(add i32:$src1, i32:$src2),
          (ADD i32:$src1, i32:$src2)>;
@ -283,7 +307,7 @@ def : Pat<(add i32:$src1, i32:$src2),
 //===- Test a simple pattern with an intrinsic. ---------------------------===//
 //

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 4*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 5*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_INTRINSIC,
 // CHECK-NEXT:    // MIs[0] dst
@ -302,14 +326,14 @@ def : Pat<(add i32:$src1, i32:$src2),
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 4: @[[LABEL]]
+// CHECK-NEXT:  // Label 5: @[[LABEL]]

 def MOV : I<(outs GPR32:$dst), (ins GPR32:$src1),
            [(set GPR32:$dst, (int_mytarget_nop GPR32:$src1))]>;

 //===- Test a nested instruction match. -----------------------------------===//

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 5*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 6*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckFeatures, GIFBS_HasA,
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_RecordInsn, /*DefineMI*/1, /*MI*/0, /*OpIdx*/1, // MIs[1]
@ -342,10 +366,10 @@ def MOV : I<(outs GPR32:$dst), (ins GPR32:$src1),
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 5: @[[LABEL]]
+// CHECK-NEXT:  // Label 6: @[[LABEL]]

 // We also get a second rule by commutativity.
-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 6*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 7*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckFeatures, GIFBS_HasA,
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_RecordInsn, /*DefineMI*/1, /*MI*/0, /*OpIdx*/2,
@ -378,7 +402,7 @@ def MOV : I<(outs GPR32:$dst), (ins GPR32:$src1),
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 6: @[[LABEL]]
+// CHECK-NEXT:  // Label 7: @[[LABEL]]

 def MULADD : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3),
               [(set GPR32:$dst,
@ -387,7 +411,7 @@ def MULADD : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3),

 //===- Test another simple pattern with regclass operands. ----------------===//

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 7*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 8*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckFeatures, GIFBS_HasA_HasB_HasC,
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_MUL,
@ -408,7 +432,7 @@ def MULADD : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3),
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 7: @[[LABEL]]
+// CHECK-NEXT:  // Label 8: @[[LABEL]]

 def MUL : I<(outs GPR32:$dst), (ins GPR32:$src2, GPR32:$src1),
             [(set GPR32:$dst, (mul GPR32:$src1, GPR32:$src2))]>,
@ -416,7 +440,7 @@ def MUL : I<(outs GPR32:$dst), (ins GPR32:$src2, GPR32:$src1),

 //===- Test a more complex multi-instruction match. -----------------------===//

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 8*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 9*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckFeatures, GIFBS_HasA,
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_RecordInsn, /*DefineMI*/1, /*MI*/0, /*OpIdx*/1, // MIs[1]
@ -461,7 +485,7 @@ def MUL : I<(outs GPR32:$dst), (ins GPR32:$src2, GPR32:$src1),
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 8: @[[LABEL]]
+// CHECK-NEXT:  // Label 9: @[[LABEL]]

 def INSNBOB : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3, GPR32:$src4),
                 [(set GPR32:$dst,
@ -471,7 +495,7 @@ def INSNBOB : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3, G
 //===- Test a pattern with ComplexPattern operands. -----------------------===//
 //

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 9*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 10*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_SUB,
 // CHECK-NEXT:    // MIs[0] dst
@ -491,7 +515,7 @@ def INSNBOB : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3, G
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 9: @[[LABEL]]
+// CHECK-NEXT:  // Label 10: @[[LABEL]]

 def INSN1 : I<(outs GPR32:$dst), (ins GPR32:$src1, complex:$src2), []>;
 def : Pat<(sub GPR32:$src1, complex:$src2), (INSN1 GPR32:$src1, complex:$src2)>;
@ -499,7 +523,7 @@ def : Pat<(sub GPR32:$src1, complex:$src2), (INSN1 GPR32:$src1, complex:$src2)>;
 //===- Test a simple pattern with a default operand. ----------------------===//
 //

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 10*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 11*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_XOR,
 // CHECK-NEXT:    // MIs[0] dst
@ -519,7 +543,7 @@ def : Pat<(sub GPR32:$src1, complex:$src2), (INSN1 GPR32:$src1, complex:$src2)>;
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 10: @[[LABEL]]
+// CHECK-NEXT:  // Label 11: @[[LABEL]]

 // The -2 is just to distinguish it from the 'not' case below.
 def XORI : I<(outs GPR32:$dst), (ins m1:$src2, GPR32:$src1),
@ -528,7 +552,7 @@ def XORI : I<(outs GPR32:$dst), (ins m1:$src2, GPR32:$src1),
 //===- Test a simple pattern with a default register operand. -------------===//
 //

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 11*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 12*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_XOR,
 // CHECK-NEXT:    // MIs[0] dst
@ -548,7 +572,7 @@ def XORI : I<(outs GPR32:$dst), (ins m1:$src2, GPR32:$src1),
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 11: @[[LABEL]]
+// CHECK-NEXT:  // Label 12: @[[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:$src1),
@ -557,7 +581,7 @@ def XOR : I<(outs GPR32:$dst), (ins Z:$src2, GPR32:$src1),
 //===- Test a simple pattern with a multiple default operands. ------------===//
 //

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 12*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 13*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_XOR,
 // CHECK-NEXT:    // MIs[0] dst
@ -578,7 +602,7 @@ def XOR : I<(outs GPR32:$dst), (ins Z:$src2, GPR32:$src1),
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 12: @[[LABEL]]
+// CHECK-NEXT:  // Label 13: @[[LABEL]]

 // The -4 is just to distinguish it from the other 'not' cases.
 def XORlike : I<(outs GPR32:$dst), (ins m1Z:$src2, GPR32:$src1),
@ -587,7 +611,7 @@ def XORlike : I<(outs GPR32:$dst), (ins m1Z:$src2, GPR32:$src1),
 //===- Test a simple pattern with multiple operands with defaults. --------===//
 //

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 13*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 14*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_XOR,
 // CHECK-NEXT:    // MIs[0] dst
@ -609,7 +633,7 @@ def XORlike : I<(outs GPR32:$dst), (ins m1Z:$src2, GPR32:$src1),
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 13: @[[LABEL]]
+// CHECK-NEXT:  // Label 14: @[[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),
@ -620,7 +644,7 @@ def XORManyDefaults : I<(outs GPR32:$dst), (ins m1Z:$src3, Z:$src2, GPR32:$src1)
 // This must precede the 3-register variants because constant immediates have
 // priority over register banks.

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 14*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 15*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/3,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_XOR,
 // CHECK-NEXT:    // MIs[0] dst
@ -640,7 +664,7 @@ def XORManyDefaults : I<(outs GPR32:$dst), (ins m1Z:$src3, Z:$src2, GPR32:$src1)
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 14: @[[LABEL]]
+// CHECK-NEXT:  // Label 15: @[[LABEL]]

 def ORN : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2), []>;
 def : Pat<(not GPR32:$Wm), (ORN R0, GPR32:$Wm)>;
@ -648,7 +672,7 @@ def : Pat<(not GPR32:$Wm), (ORN R0, GPR32:$Wm)>;
 //===- Test a COPY_TO_REGCLASS --------------------------------------------===//
 //

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 15*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 16*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/2,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_BITCAST,
 // CHECK-NEXT:    // MIs[0] dst
@ -661,14 +685,14 @@ def : Pat<(not GPR32:$Wm), (ORN R0, GPR32:$Wm)>;
 // CHECK-NEXT:    GIR_MutateOpcode, /*InsnID*/0, /*RecycleInsnID*/0, /*Opcode*/TargetOpcode::COPY,
 // CHECK-NEXT:    GIR_ConstrainOperandRC, /*InsnID*/0, /*Op*/0, /*RC GPR32*/1,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 15: @[[LABEL]]
+// CHECK-NEXT:  // Label 16: @[[LABEL]]

 def : Pat<(i32 (bitconvert FPR32:$src1)),
          (COPY_TO_REGCLASS FPR32:$src1, GPR32)>;

 //===- Test a simple pattern with just a specific leaf immediate. ---------===//

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 16*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 17*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/2,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_CONSTANT,
 // CHECK-NEXT:    // MIs[0] dst
@ -682,13 +706,13 @@ def : Pat<(i32 (bitconvert FPR32:$src1)),
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 16: @[[LABEL]]
+// CHECK-NEXT:  // Label 17: @[[LABEL]]

 def MOV1 : I<(outs GPR32:$dst), (ins), [(set GPR32:$dst, 1)]>;

 //===- Test a simple pattern with a leaf immediate and a predicate. -------===//

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 17*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 18*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/2,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_CONSTANT,
 // CHECK-NEXT:    GIM_CheckI64ImmPredicate, /*MI*/0, /*Predicate*/GIPFP_I64_Predicate_simm8,
@ -704,14 +728,14 @@ def MOV1 : I<(outs GPR32:$dst), (ins), [(set GPR32:$dst, 1)]>;
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 17: @[[LABEL]]
+// CHECK-NEXT:  // Label 18: @[[LABEL]]

 def simm8 : ImmLeaf<i32, [{ return isInt<8>(Imm); }]>;
 def MOVimm8 : I<(outs GPR32:$dst), (ins i32imm:$imm), [(set GPR32:$dst, simm8:$imm)]>;

 //===- Same again but use an IntImmLeaf. ----------------------------------===//

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 18*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 19*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/2,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_CONSTANT,
 // CHECK-NEXT:    GIM_CheckAPIntImmPredicate, /*MI*/0, /*Predicate*/GIPFP_APInt_Predicate_simm9,
@ -727,14 +751,14 @@ def MOVimm8 : I<(outs GPR32:$dst), (ins i32imm:$imm), [(set GPR32:$dst, simm8:$i
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 18: @[[LABEL]]
+// CHECK-NEXT:  // Label 19: @[[LABEL]]

 def simm9 : IntImmLeaf<i32, [{ return isInt<9>(Imm->getSExtValue()); }]>;
 def MOVimm9 : I<(outs GPR32:$dst), (ins i32imm:$imm), [(set GPR32:$dst, simm9:$imm)]>;

 //===- Test a simple pattern with just a leaf immediate. ------------------===//

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 19*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 20*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/2,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_CONSTANT,
 // CHECK-NEXT:    // MIs[0] dst
@ -749,13 +773,13 @@ def MOVimm9 : I<(outs GPR32:$dst), (ins i32imm:$imm), [(set GPR32:$dst, simm9:$i
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 19: @[[LABEL]]
+// CHECK-NEXT:  // Label 20: @[[LABEL]]

 def MOVimm : I<(outs GPR32:$dst), (ins i32imm:$imm), [(set GPR32:$dst, imm:$imm)]>;

 //===- Test a simple pattern with a FP immediate and a predicate. ---------===//

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 20*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 21*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/2,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_FCONSTANT,
 // CHECK-NEXT:    GIM_CheckAPFloatImmPredicate, /*MI*/0, /*Predicate*/GIPFP_APFloat_Predicate_fpimmz,
@ -771,14 +795,14 @@ def MOVimm : I<(outs GPR32:$dst), (ins i32imm:$imm), [(set GPR32:$dst, imm:$imm)
 // CHECK-NEXT:    GIR_EraseFromParent, /*InsnID*/0,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 20: @[[LABEL]]
+// CHECK-NEXT:  // Label 21: @[[LABEL]]

 def fpimmz : FPImmLeaf<f32, [{ return Imm->isExactlyValue(0.0); }]>;
 def MOVfpimmz : I<(outs FPR32:$dst), (ins f32imm:$imm), [(set FPR32:$dst, fpimmz:$imm)]>;

 //===- Test a pattern with an MBB operand. --------------------------------===//

-// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 21*/ [[LABEL:[0-9]+]],
+// CHECK-NEXT:  GIM_Try, /*On fail goto*//*Label 22*/ [[LABEL:[0-9]+]],
 // CHECK-NEXT:    GIM_CheckNumOperands, /*MI*/0, /*Expected*/1,
 // CHECK-NEXT:    GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_BR,
 // CHECK-NEXT:    // MIs[0] target
@ -787,7 +811,7 @@ def MOVfpimmz : I<(outs FPR32:$dst), (ins f32imm:$imm), [(set FPR32:$dst, fpimmz
 // CHECK-NEXT:    GIR_MutateOpcode, /*InsnID*/0, /*RecycleInsnID*/0, /*Opcode*/MyTarget::BR,
 // CHECK-NEXT:    GIR_ConstrainSelectedInstOperands, /*InsnID*/0,
 // CHECK-NEXT:    GIR_Done,
-// CHECK-NEXT:  // Label 21: @[[LABEL]]
+// CHECK-NEXT:  // Label 22: @[[LABEL]]

 def BR : I<(outs), (ins unknown:$target),
            [(br bb:$target)]>;
--- a/utils/TableGen/GlobalISelEmitter.cpp
+++ b/utils/TableGen/GlobalISelEmitter.cpp
@ -478,14 +478,21 @@ class RuleMatcher {
  /// emitCaptureOpcodes().
  DefinedInsnVariablesMap InsnVariableIDs;

+  /// A map of named operands defined by the matchers that may be referenced by
+  /// the renderers.
+  StringMap<OperandMatcher *> DefinedOperands;
+
  /// ID for the next instruction variable defined with defineInsnVar()
  unsigned NextInsnVarID;

  std::vector<Record *> RequiredFeatures;

+  ArrayRef<SMLoc> SrcLoc;
+
 public:
-  RuleMatcher()
-      : Matchers(), Actions(), InsnVariableIDs(), NextInsnVarID(0) {}
+  RuleMatcher(ArrayRef<SMLoc> SrcLoc)
+      : Matchers(), Actions(), InsnVariableIDs(), DefinedOperands(),
+        NextInsnVarID(0), SrcLoc(SrcLoc) {}
  RuleMatcher(RuleMatcher &&Other) = default;
  RuleMatcher &operator=(RuleMatcher &&Other) = default;

@ -513,7 +520,10 @@ public:
    return make_range(defined_insn_vars_begin(), defined_insn_vars_end());
  }

+  void defineOperand(StringRef SymbolicName, OperandMatcher &OM);
+
  const InstructionMatcher &getInstructionMatcher(StringRef SymbolicName) const;
+  const OperandMatcher &getOperandMatcher(StringRef Name) const;

  void emitCaptureOpcodes(MatchTable &Table);

@ -544,10 +554,10 @@ private:
 public:
  /// Construct a new operand predicate and add it to the matcher.
  template <class Kind, class... Args>
-  Kind &addPredicate(Args&&... args) {
+  Optional<Kind *> addPredicate(Args&&... args) {
    Predicates.emplace_back(
        llvm::make_unique<Kind>(std::forward<Args>(args)...));
-    return *static_cast<Kind *>(Predicates.back().get());
+    return static_cast<Kind *>(Predicates.back().get());
  }

  typename PredicateVec::const_iterator predicates_begin() const {
@ -593,6 +603,7 @@ public:
  /// but OPM_Int must have priority over OPM_RegBank since constant integers
  /// are represented by a virtual register defined by a G_CONSTANT instruction.
  enum PredicateKind {
+    OPM_Tie,
    OPM_ComplexPattern,
    OPM_IntrinsicID,
    OPM_Instruction,
@ -612,17 +623,6 @@ public:

  PredicateKind getKind() const { return Kind; }

-  /// Return the OperandMatcher for the specified operand or nullptr if there
-  /// isn't one by that name in this operand predicate matcher.
-  ///
-  /// InstructionOperandMatcher is the only subclass that can return non-null
-  /// for this.
-  virtual Optional<const OperandMatcher *>
-  getOptionalOperand(StringRef SymbolicName) const {
-    assert(!SymbolicName.empty() && "Cannot lookup unnamed operand");
-    return None;
-  }
-
  /// Emit MatchTable opcodes to capture instructions into the MIs table.
  ///
  /// Only InstructionOperandMatcher needs to do anything for this method the
@ -651,6 +651,23 @@ PredicateListMatcher<OperandPredicateMatcher>::getNoPredicateComment() const {
  return "No operand predicates";
 }

+/// Generates code to check that a register operand is defined by the same exact
+/// one as another.
+class SameOperandMatcher : public OperandPredicateMatcher {
+  std::string TiedTo;
+
+public:
+  SameOperandMatcher(StringRef TiedTo)
+      : OperandPredicateMatcher(OPM_Tie), TiedTo(TiedTo) {}
+
+  static bool classof(const OperandPredicateMatcher *P) {
+    return P->getKind() == OPM_Tie;
+  }
+
+  void emitPredicateOpcodes(MatchTable &Table, RuleMatcher &Rule,
+                            unsigned InsnVarID, unsigned OpIdx) const override;
+};
+
 /// Generates code to check that an operand is a particular LLT.
 class LLTOperandMatcher : public OperandPredicateMatcher {
 protected:
@ -857,19 +874,6 @@ public:
           llvm::to_string(OpIdx) + ")";
  }

-  Optional<const OperandMatcher *>
-  getOptionalOperand(StringRef DesiredSymbolicName) const {
-    assert(!DesiredSymbolicName.empty() && "Cannot lookup unnamed operand");
-    if (DesiredSymbolicName == SymbolicName)
-      return this;
-    for (const auto &OP : predicates()) {
-      const auto &MaybeOperand = OP->getOptionalOperand(DesiredSymbolicName);
-      if (MaybeOperand.hasValue())
-        return MaybeOperand.getValue();
-    }
-    return None;
-  }
-
  InstructionMatcher &getInstructionMatcher() const { return Insn; }

  /// Emit MatchTable opcodes to capture instructions into the MIs table.
@ -930,8 +934,27 @@ public:
  unsigned getAllocatedTemporariesBaseID() const {
    return AllocatedTemporariesBaseID;
  }
+
+  bool isSameAsAnotherOperand() const {
+    for (const auto &Predicate : predicates())
+      if (isa<SameOperandMatcher>(Predicate))
+        return true;
+    return false;
+  }
 };

+// Specialize OperandMatcher::addPredicate() to refrain from adding redundant
+// predicates.
+template <>
+template <class Kind, class... Args>
+Optional<Kind *>
+PredicateListMatcher<OperandPredicateMatcher>::addPredicate(Args &&... args) {
+  if (static_cast<OperandMatcher *>(this)->isSameAsAnotherOperand())
+    return None;
+  Predicates.emplace_back(llvm::make_unique<Kind>(std::forward<Args>(args)...));
+  return static_cast<Kind *>(Predicates.back().get());
+}
+
 unsigned ComplexPatternOperandMatcher::getAllocatedTemporariesBaseID() const {
  return Operand.getAllocatedTemporariesBaseID();
 }
@ -1088,6 +1111,8 @@ class InstructionMatcher
 protected:
  typedef std::vector<std::unique_ptr<OperandMatcher>> OperandVec;

+  RuleMatcher &Rule;
+
  /// The operands to match. All rendered operands must be present even if the
  /// condition is always true.
  OperandVec Operands;
@ -1095,13 +1120,19 @@ protected:
  std::string SymbolicName;

 public:
-  InstructionMatcher(StringRef SymbolicName) : SymbolicName(SymbolicName) {}
+  InstructionMatcher(RuleMatcher &Rule, StringRef SymbolicName)
+      : Rule(Rule), SymbolicName(SymbolicName) {}
+
+  RuleMatcher &getRuleMatcher() const { return Rule; }

  /// Add an operand to the matcher.
  OperandMatcher &addOperand(unsigned OpIdx, const std::string &SymbolicName,
                             unsigned AllocatedTemporariesBaseID) {
    Operands.emplace_back(new OperandMatcher(*this, OpIdx, SymbolicName,
                                             AllocatedTemporariesBaseID));
+    if (!SymbolicName.empty())
+      Rule.defineOperand(SymbolicName, *Operands.back());
+
    return *Operands.back();
  }

@ -1115,24 +1146,6 @@ public:
    llvm_unreachable("Failed to lookup operand");
  }

-  Optional<const OperandMatcher *>
-  getOptionalOperand(StringRef SymbolicName) const {
-    assert(!SymbolicName.empty() && "Cannot lookup unnamed operand");
-    for (const auto &Operand : Operands) {
-      const auto &OM = Operand->getOptionalOperand(SymbolicName);
-      if (OM.hasValue())
-        return OM.getValue();
-    }
-    return None;
-  }
-
-  const OperandMatcher &getOperand(StringRef SymbolicName) const {
-    Optional<const OperandMatcher *>OM = getOptionalOperand(SymbolicName);
-    if (OM.hasValue())
-      return *OM.getValue();
-    llvm_unreachable("Failed to lookup operand");
-  }
-
  StringRef getSymbolicName() const { return SymbolicName; }
  unsigned getNumOperands() const { return Operands.size(); }
  OperandVec::iterator operands_begin() { return Operands.begin(); }
@ -1233,9 +1246,9 @@ protected:
  std::unique_ptr<InstructionMatcher> InsnMatcher;

 public:
-  InstructionOperandMatcher(StringRef SymbolicName)
+  InstructionOperandMatcher(RuleMatcher &Rule, StringRef SymbolicName)
      : OperandPredicateMatcher(OPM_Instruction),
-        InsnMatcher(new InstructionMatcher(SymbolicName)) {}
+        InsnMatcher(new InstructionMatcher(Rule, SymbolicName)) {}

  static bool classof(const OperandPredicateMatcher *P) {
    return P->getKind() == OPM_Instruction;
@ -1243,12 +1256,6 @@ public:

  InstructionMatcher &getInsnMatcher() const { return *InsnMatcher; }

-  Optional<const OperandMatcher *>
-  getOptionalOperand(StringRef SymbolicName) const override {
-    assert(!SymbolicName.empty() && "Cannot lookup unnamed operand");
-    return InsnMatcher->getOptionalOperand(SymbolicName);
-  }
-
  void emitCaptureOpcodes(MatchTable &Table, RuleMatcher &Rule,
                          unsigned InsnID, unsigned OpIdx) const override {
    unsigned InsnVarID = Rule.defineInsnVar(Table, *InsnMatcher, InsnID, OpIdx);
@ -1316,7 +1323,7 @@ public:
  const StringRef getSymbolicName() const { return SymbolicName; }

  void emitRenderOpcodes(MatchTable &Table, RuleMatcher &Rule) const override {
-    const OperandMatcher &Operand = Matched.getOperand(SymbolicName);
+    const OperandMatcher &Operand = Rule.getOperandMatcher(SymbolicName);
    unsigned OldInsnVarID = Rule.getInsnVarID(Operand.getInstructionMatcher());
    Table << MatchTable::Opcode("GIR_Copy") << MatchTable::Comment("NewInsnID")
          << MatchTable::IntValue(NewInsnID) << MatchTable::Comment("OldInsnID")
@ -1416,7 +1423,7 @@ public:
  const StringRef getSymbolicName() const { return SymbolicName; }

  void emitRenderOpcodes(MatchTable &Table, RuleMatcher &Rule) const override {
-    const OperandMatcher &Operand = Matched.getOperand(SymbolicName);
+    const OperandMatcher &Operand = Rule.getOperandMatcher(SymbolicName);
    unsigned OldInsnVarID = Rule.getInsnVarID(Operand.getInstructionMatcher());
    Table << MatchTable::Opcode("GIR_CopySubReg")
          << MatchTable::Comment("NewInsnID") << MatchTable::IntValue(NewInsnID)
@ -1556,13 +1563,13 @@ private:
  std::vector<std::unique_ptr<OperandRenderer>> OperandRenderers;

  /// True if the instruction can be built solely by mutating the opcode.
-  bool canMutate() const {
+  bool canMutate(RuleMatcher &Rule) const {
    if (OperandRenderers.size() != Matched.getNumOperands())
      return false;

    for (const auto &Renderer : enumerate(OperandRenderers)) {
      if (const auto *Copy = dyn_cast<CopyRenderer>(&*Renderer.value())) {
-        const OperandMatcher &OM = Matched.getOperand(Copy->getSymbolicName());
+        const OperandMatcher &OM = Rule.getOperandMatcher(Copy->getSymbolicName());
        if (&Matched != &OM.getInstructionMatcher() ||
            OM.getOperandIndex() != Renderer.index())
          return false;
@ -1587,7 +1594,7 @@ public:

  void emitActionOpcodes(MatchTable &Table, RuleMatcher &Rule,
                         unsigned RecycleInsnID) const override {
-    if (canMutate()) {
+    if (canMutate(Rule)) {
      Table << MatchTable::Opcode("GIR_MutateOpcode")
            << MatchTable::Comment("InsnID") << MatchTable::IntValue(InsnID)
            << MatchTable::Comment("RecycleInsnID")
@ -1695,7 +1702,7 @@ public:
 };

 InstructionMatcher &RuleMatcher::addInstructionMatcher(StringRef SymbolicName) {
-  Matchers.emplace_back(new InstructionMatcher(SymbolicName));
+  Matchers.emplace_back(new InstructionMatcher(*this, SymbolicName));
  return *Matchers.back();
 }

@ -1740,6 +1747,17 @@ unsigned RuleMatcher::getInsnVarID(const InstructionMatcher &InsnMatcher) const
  llvm_unreachable("Matched Insn was not captured in a local variable");
 }

+void RuleMatcher::defineOperand(StringRef SymbolicName, OperandMatcher &OM) {
+  if (DefinedOperands.find(SymbolicName) == DefinedOperands.end()) {
+    DefinedOperands[SymbolicName] = &OM;
+    return;
+  }
+
+  // If the operand is already defined, then we must ensure both references in
+  // the matcher have the exact same node.
+  OM.addPredicate<SameOperandMatcher>(OM.getSymbolicName());
+}
+
 const InstructionMatcher &
 RuleMatcher::getInstructionMatcher(StringRef SymbolicName) const {
  for (const auto &I : InsnVariableIDs)
@ -1749,6 +1767,16 @@ RuleMatcher::getInstructionMatcher(StringRef SymbolicName) const {
      ("Failed to lookup instruction " + SymbolicName).str().c_str());
 }

+const OperandMatcher &
+RuleMatcher::getOperandMatcher(StringRef Name) const {
+  const auto &I = DefinedOperands.find(Name);
+
+  if (I == DefinedOperands.end())
+    PrintFatalError(SrcLoc, "Operand " + Name + " was not declared in matcher");
+
+  return *I->second;
+}
+
 /// Emit MatchTable opcodes to check the shape of the match and capture
 /// instructions into local variables.
 void RuleMatcher::emitCaptureOpcodes(MatchTable &Table) {
@ -1908,6 +1936,23 @@ bool OperandPredicateMatcher::isHigherPriorityThan(
  return Kind < B.Kind;
 }

+void SameOperandMatcher::emitPredicateOpcodes(MatchTable &Table,
+                                              RuleMatcher &Rule,
+                                              unsigned InsnVarID,
+                                              unsigned OpIdx) const {
+  const OperandMatcher &OtherOM = Rule.getOperandMatcher(TiedTo);
+  unsigned OtherInsnVarID = Rule.getInsnVarID(OtherOM.getInstructionMatcher());
+
+  Table << MatchTable::Opcode("GIM_CheckIsSameOperand")
+        << MatchTable::Comment("MI") << MatchTable::IntValue(InsnVarID)
+        << MatchTable::Comment("OpIdx") << MatchTable::IntValue(OpIdx)
+        << MatchTable::Comment("OtherMI")
+        << MatchTable::IntValue(OtherInsnVarID)
+        << MatchTable::Comment("OtherOpIdx")
+        << MatchTable::IntValue(OtherOM.getOperandIndex())
+        << MatchTable::LineBreak;
+}
+
 //===- GlobalISelEmitter class --------------------------------------------===//

 class GlobalISelEmitter {
@ -1947,7 +1992,8 @@ private:
  Expected<BuildMIAction &>
  createAndImportInstructionRenderer(RuleMatcher &M, const TreePatternNode *Dst,
                                     const InstructionMatcher &InsnMatcher);
-  Error importExplicitUseRenderer(BuildMIAction &DstMIBuilder,
+  Error importExplicitUseRenderer(RuleMatcher &Rule,
+                                  BuildMIAction &DstMIBuilder,
                                  TreePatternNode *DstChild,
                                  const InstructionMatcher &InsnMatcher) const;
  Error importDefaultOperandRenderers(BuildMIAction &DstMIBuilder,
@ -2065,7 +2111,8 @@ GlobalISelEmitter::createAndImportSelDAGMatcher(InstructionMatcher &InsnMatcher,
  if (Src->isLeaf()) {
    Init *SrcInit = Src->getLeafValue();
    if (IntInit *SrcIntInit = dyn_cast<IntInit>(SrcInit)) {
-      OperandMatcher &OM = InsnMatcher.addOperand(OpIdx++, "", TempOpIdx);
+      OperandMatcher &OM =
+          InsnMatcher.addOperand(OpIdx++, Src->getName(), TempOpIdx);
      OM.addPredicate<LiteralIntOperandMatcher>(SrcIntInit->getValue());
    } else
      return failedImport(
@ -2116,6 +2163,8 @@ Error GlobalISelEmitter::importChildMatcher(InstructionMatcher &InsnMatcher,
                                            unsigned &TempOpIdx) const {
  OperandMatcher &OM =
      InsnMatcher.addOperand(OpIdx, SrcChild->getName(), TempOpIdx);
+  if (OM.isSameAsAnotherOperand())
+    return Error::success();

  ArrayRef<TypeSetByHwMode> ChildTypes = SrcChild->getExtTypes();
  if (ChildTypes.size() != 1)
@ -2141,9 +2190,17 @@ Error GlobalISelEmitter::importChildMatcher(InstructionMatcher &InsnMatcher,

  // Check for nested instructions.
  if (!SrcChild->isLeaf()) {
+    auto MaybeInsnOperand = OM.addPredicate<InstructionOperandMatcher>(
+        InsnMatcher.getRuleMatcher(), SrcChild->getName());
+    if (!MaybeInsnOperand.hasValue()) {
+      // This isn't strictly true. If the user were to provide exactly the same
+      // matchers as the original operand then we could allow it. However, it's
+      // simpler to not permit the redundant specification.
+      return failedImport("Nested instruction cannot be the same as another operand");
+    }
+
    // Map the node to a gMIR instruction.
-    InstructionOperandMatcher &InsnOperand =
-        OM.addPredicate<InstructionOperandMatcher>(SrcChild->getName());
+    InstructionOperandMatcher &InsnOperand = **MaybeInsnOperand;
    auto InsnMatcherOrError = createAndImportSelDAGMatcher(
        InsnOperand.getInsnMatcher(), SrcChild, TempOpIdx);
    if (auto Error = InsnMatcherOrError.takeError())
@ -2203,7 +2260,7 @@ Error GlobalISelEmitter::importChildMatcher(InstructionMatcher &InsnMatcher,
 }

 Error GlobalISelEmitter::importExplicitUseRenderer(
-    BuildMIAction &DstMIBuilder, TreePatternNode *DstChild,
+    RuleMatcher &Rule, BuildMIAction &DstMIBuilder, TreePatternNode *DstChild,
    const InstructionMatcher &InsnMatcher) const {
  if (DstChild->getTransformFn() != nullptr) {
    return failedImport("Dst pattern child has transform fn " +
@ -2272,7 +2329,7 @@ Error GlobalISelEmitter::importExplicitUseRenderer(
        return failedImport(
            "SelectionDAG ComplexPattern not mapped to GlobalISel");

-      const OperandMatcher &OM = InsnMatcher.getOperand(DstChild->getName());
+      const OperandMatcher &OM = Rule.getOperandMatcher(DstChild->getName());
      DstMIBuilder.addRenderer<RenderComplexPatternOperand>(
          0, *ComplexPattern->second, DstChild->getName(),
          OM.getAllocatedTemporariesBaseID());
@ -2373,7 +2430,7 @@ Expected<BuildMIAction &> GlobalISelEmitter::createAndImportInstructionRenderer(
    }

    if (auto Error = importExplicitUseRenderer(
-            DstMIBuilder, Dst->getChild(Child), InsnMatcher))
+            M, DstMIBuilder, Dst->getChild(Child), InsnMatcher))
      return std::move(Error);
    ++Child;
  }
@ -2426,7 +2483,7 @@ Error GlobalISelEmitter::importImplicitDefRenderers(

 Expected<RuleMatcher> GlobalISelEmitter::runOnPattern(const PatternToMatch &P) {
  // Keep track of the matchers and actions to emit.
-  RuleMatcher M;
+  RuleMatcher M(P.getSrcRecord()->getLoc());
  M.addAction<DebugCommentAction>(P);

  if (auto Error = importRulePredicates(M, P.getPredicates()))
@ -2465,6 +2522,7 @@ Expected<RuleMatcher> GlobalISelEmitter::runOnPattern(const PatternToMatch &P) {

      OperandMatcher &OM0 = InsnMatcher.getOperand(0);
      OM0.setSymbolicName(DstIOperand.Name);
+      M.defineOperand(OM0.getSymbolicName(), OM0);
      OM0.addPredicate<RegisterBankOperandMatcher>(RC);

      auto &DstMIBuilder = M.addAction<BuildMIAction>(0, &DstI, InsnMatcher);
@ -2525,6 +2583,7 @@ Expected<RuleMatcher> GlobalISelEmitter::runOnPattern(const PatternToMatch &P) {

    OperandMatcher &OM = InsnMatcher.getOperand(OpIdx);
    OM.setSymbolicName(DstIOperand.Name);
+    M.defineOperand(OM.getSymbolicName(), OM);
    OM.addPredicate<RegisterBankOperandMatcher>(
        Target.getRegisterClass(DstIOpRec));
    ++OpIdx;