[TableGen][GlobalISel] Fix handling of zero_reg

When generating matching tables for GlobalISel, TableGen would output
"::zero_reg" whenever encountering the zero_reg, which in turn would
result in compilation error. This patch fixes that by instead outputting
NoRegister (== 0), which is the same result that TableGen produces when
generating matching tables for ISelDAG.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D86215

llvm/lib/Target/ARM/ARMInstructionSelector.cpp

@@ -164,8 +164,6 @@ createARMInstructionSelector(const ARMBaseTargetMachine &TM,
 }
 }
 
-const unsigned zero_reg = 0;
-
 #define GET_GLOBALISEL_IMPL
 #include "ARMGenGlobalISel.inc"
 #undef GET_GLOBALISEL_IMPL

llvm/test/TableGen/GlobalISelEmitter-zero-reg.td

@@ -0,0 +1,42 @@
+// RUN: llvm-tblgen -gen-global-isel -optimize-match-table=false -I %p/../../include -I %p/Common %s -o - < %s | FileCheck %s
+
+include "llvm/Target/Target.td"
+include "GlobalISelEmitterCommon.td"
+
+def P0 : Register<"p0"> { let Namespace = "MyTarget"; }
+def PR32 : RegisterClass<"MyTarget", [i32], 32, (add P0)>;
+def PR32Op : RegisterOperand<PR32>;
+
+def pred : PredicateOperand<OtherVT,
+                            (ops PR32:$FR),
+                            (ops (i32 zero_reg))> {}
+class PredI<dag OOps, dag IOps, list<dag> Pat>
+  : Instruction {
+  let Namespace = "MyTarget";
+  let OutOperandList = OOps;
+  let InOperandList = !con(IOps, (ins pred:$pred));
+  let Pattern = Pat;
+}
+
+def INST : PredI<(outs GPR32:$dst), (ins GPR32:$src), []>;
+
+// CHECK: GIM_CheckNumOperands, /*MI*/0, /*Expected*/2,
+// CHECK-NEXT: GIM_CheckOpcode, /*MI*/0, TargetOpcode::G_LOAD,
+// CHECK-NEXT: GIM_CheckMemorySizeEqualToLLT, /*MI*/0, /*MMO*/0, /*OpIdx*/0,
+// CHECK-NEXT: GIM_CheckAtomicOrdering, /*MI*/0, /*Order*/(int64_t)AtomicOrdering::NotAtomic,
+// 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_CheckPointerToAny, /*MI*/0, /*Op*/1, /*SizeInBits*/32,
+// CHECK-NEXT: GIM_CheckRegBankForClass, /*MI*/0, /*Op*/1, /*RC*/MyTarget::GPR32RegClassID,
+// CHECK-NEXT: // (ld:{ *:[i32] } GPR32:{ *:[i32] }:$src)<<P:Predicate_unindexedload>><<P:Predicate_load>>  =>  (INST:{ *:[i32] } GPR32:{ *:[i32] }:$src)
+// CHECK-NEXT: GIR_BuildMI, /*InsnID*/0, /*Opcode*/MyTarget::INST,
+// 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_AddRegister, /*InsnID*/0, MyTarget::NoRegister, /*AddRegisterRegFlags*/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,
+def : Pat<(i32 (load GPR32:$src)),
+          (INST GPR32:$src)>;

llvm/utils/TableGen/CodeGenTarget.cpp

@@ -266,6 +266,11 @@ StringRef CodeGenTarget::getInstNamespace() const {
   return "";
 }
 
+StringRef CodeGenTarget::getRegNamespace() const {
+  auto &RegClasses = RegBank->getRegClasses();
+  return RegClasses.size() > 0 ? RegClasses.front().Namespace : "";
+}
+
 Record *CodeGenTarget::getInstructionSet() const {
   return TargetRec->getValueAsDef("InstructionSet");
 }

llvm/utils/TableGen/CodeGenTarget.h

@@ -73,6 +73,9 @@ public:
   ///
   StringRef getInstNamespace() const;
 
+  /// getRegNamespace - Return the target-specific register namespace.
+  StringRef getRegNamespace() const;
+
   /// getInstructionSet - Return the InstructionSet object.
   ///
   Record *getInstructionSet() const;

llvm/utils/TableGen/GlobalISelEmitter.cpp

@@ -2729,12 +2729,13 @@ protected:
   unsigned InsnID;
   const Record *RegisterDef;
   bool IsDef;
+  const CodeGenTarget &Target;
 
 public:
-  AddRegisterRenderer(unsigned InsnID, const Record *RegisterDef,
-                      bool IsDef = false)
+  AddRegisterRenderer(unsigned InsnID, const CodeGenTarget &Target,
+                      const Record *RegisterDef, bool IsDef = false)
       : OperandRenderer(OR_Register), InsnID(InsnID), RegisterDef(RegisterDef),
-        IsDef(IsDef) {}
+        IsDef(IsDef), Target(Target) {}
 
   static bool classof(const OperandRenderer *R) {
     return R->getKind() == OR_Register;
@@ -2742,13 +2743,17 @@ public:
 
   void emitRenderOpcodes(MatchTable &Table, RuleMatcher &Rule) const override {
     Table << MatchTable::Opcode("GIR_AddRegister")
-          << MatchTable::Comment("InsnID") << MatchTable::IntValue(InsnID)
-          << MatchTable::NamedValue(
-                 (RegisterDef->getValue("Namespace")
-                      ? RegisterDef->getValueAsString("Namespace")
-                      : ""),
-                 RegisterDef->getName())
-          << MatchTable::Comment("AddRegisterRegFlags");
+          << MatchTable::Comment("InsnID") << MatchTable::IntValue(InsnID);
+    if (RegisterDef->getName() != "zero_reg") {
+      Table << MatchTable::NamedValue(
+                   (RegisterDef->getValue("Namespace")
+                        ? RegisterDef->getValueAsString("Namespace")
+                        : ""),
+                   RegisterDef->getName());
+    } else {
+      Table << MatchTable::NamedValue(Target.getRegNamespace(), "NoRegister");
+    }
+    Table << MatchTable::Comment("AddRegisterRegFlags");
 
     // TODO: This is encoded as a 64-bit element, but only 16 or 32-bits are
     // really needed for a physical register reference. We can pack the
@@ -4419,7 +4424,7 @@ Expected<action_iterator> GlobalISelEmitter::importExplicitUseRenderer(
       return failedImport("Dst operand has an unsupported type");
 
     if (ChildRec->isSubClassOf("Register")) {
-      DstMIBuilder.addRenderer<AddRegisterRenderer>(ChildRec);
+      DstMIBuilder.addRenderer<AddRegisterRenderer>(Target, ChildRec);
       return InsertPt;
     }
 
@@ -4479,7 +4484,8 @@ Expected<BuildMIAction &> GlobalISelEmitter::createAndImportInstructionRenderer(
         &Target.getInstruction(RK.getDef("COPY")));
     BuildMIAction &CopyToPhysRegMIBuilder =
         *static_cast<BuildMIAction *>(InsertPt->get());
-    CopyToPhysRegMIBuilder.addRenderer<AddRegisterRenderer>(PhysInput.first,
+    CopyToPhysRegMIBuilder.addRenderer<AddRegisterRenderer>(Target,
+                                                            PhysInput.first,
                                                             true);
     CopyToPhysRegMIBuilder.addRenderer<CopyPhysRegRenderer>(PhysInput.first);
   }
@@ -4870,7 +4876,7 @@ Error GlobalISelEmitter::importDefaultOperandRenderers(
         IDMIBuilder.addRenderer<TempRegRenderer>(TempRegID);
         DstMIBuilder.addRenderer<TempRegRenderer>(TempRegID);
       } else {
-        DstMIBuilder.addRenderer<AddRegisterRenderer>(Def);
+        DstMIBuilder.addRenderer<AddRegisterRenderer>(Target, Def);
       }
       continue;
     }