[GlobalISel] Add a G_JUMP_TABLE opcode

[aemerson]

Summary

This opcode generates a pointer to the address of the jump table specified by the source operand, which is a jump table index.

It will be used in conjunction with an upcoming G_BRJT opcode to support jump table codegen with GlobalISel.

[paquette]

LGTM

llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h

   }
 
   /// Build and insert \p Res = G_UMAX \p Op0, \p Op1
   MachineInstrBuilder buildUMax(const DstOp &Dst, const SrcOp &Src0,
                                 const SrcOp &Src1) {
     return buildInstr(TargetOpcode::G_UMAX, {Dst}, {Src0, Src1});
   }
 
+  /// Build and insert \p Res = G_JUMP_TABLE \p JTI
+  ///
+  /// G_JUMP_TABLE sets \p Res to the address of the jump table specified by
+  /// the jump table index \p JTI.
+  ///
+  /// \return a MachineInstrBuilder for the newly created instruction.
+  MachineInstrBuilder buildJumpTable(const LLT PtrTy, unsigned JTI);
+
   virtual MachineInstrBuilder buildInstr(unsigned Opc, ArrayRef<DstOp> DstOps,
                                          ArrayRef<SrcOp> SrcOps,
                                          Optional<unsigned> Flags = None);
 };
 
 } // End namespace llvm.
 #endif // LLVM_CODEGEN_GLOBALISEL_MACHINEIRBUILDER_H

llvm/include/llvm/Support/TargetOpcodes.def

 HANDLE_TARGET_OPCODE(G_FNEARBYINT)
 
 /// Generic AddressSpaceCast.
 HANDLE_TARGET_OPCODE(G_ADDRSPACE_CAST)
 
 /// Generic block address
 HANDLE_TARGET_OPCODE(G_BLOCK_ADDR)
 
+/// Generic jump table address
+HANDLE_TARGET_OPCODE(G_JUMP_TABLE)
+
 // TODO: Add more generic opcodes as we move along.
 
 /// Marker for the end of the generic opcode.
 /// This is used to check if an opcode is in the range of the
 /// generic opcodes.
-HANDLE_TARGET_OPCODE_MARKER(PRE_ISEL_GENERIC_OPCODE_END, G_BLOCK_ADDR)
+HANDLE_TARGET_OPCODE_MARKER(PRE_ISEL_GENERIC_OPCODE_END, G_JUMP_TABLE)
 
 /// BUILTIN_OP_END - This must be the last enum value in this list.
 /// The target-specific post-isel opcode values start here.
 HANDLE_TARGET_OPCODE_MARKER(GENERIC_OP_END, PRE_ISEL_GENERIC_OPCODE_END)

llvm/include/llvm/Target/GenericOpcodes.td

 }
 
 def G_BLOCK_ADDR : GenericInstruction {
   let OutOperandList = (outs type0:$dst);
   let InOperandList = (ins unknown:$ba);
   let hasSideEffects = 0;
 }
 
+def G_JUMP_TABLE : GenericInstruction {
+  let OutOperandList = (outs type0:$dst);
+  let InOperandList = (ins unknown:$jti);
+  let hasSideEffects = 0;
+}
+
 //------------------------------------------------------------------------------
 // Binary ops.
 //------------------------------------------------------------------------------
 
 // Generic addition.
 def G_ADD : GenericInstruction {
   let OutOperandList = (outs type0:$dst);
   let InOperandList = (ins type0:$src1, type0:$src2);

llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp

assert(getMRI()->getType(Res).getAddressSpace() ==
              GV->getType()->getAddressSpace() &&
          "address space mismatch");
 
   return buildInstr(TargetOpcode::G_GLOBAL_VALUE)
       .addDef(Res)
       .addGlobalAddress(GV);
 }
 
+MachineInstrBuilder MachineIRBuilder::buildJumpTable(const LLT PtrTy,
+                                                     unsigned JTI) {
+  return buildInstr(TargetOpcode::G_JUMP_TABLE, {PtrTy}, {})
+      .addJumpTableIndex(JTI);
+}
+
 void MachineIRBuilder::validateBinaryOp(const LLT &Res, const LLT &Op0,
                                         const LLT &Op1) {
   assert((Res.isScalar() || Res.isVector()) && "invalid operand type");
   assert((Res == Op0 && Res == Op1) && "type mismatch");
 }
 
 void MachineIRBuilder::validateShiftOp(const LLT &Res, const LLT &Op0,
                                        const LLT &Op1) {

llvm/lib/CodeGen/MachineVerifier.cpp

case TargetOpcode::G_INSERT: {
     if (DstSize <= SrcSize)
       report("inserted size must be smaller than total register", MI);
 
     if (SrcSize + OffsetOp.getImm() > DstSize)
       report("insert writes past end of register", MI);
 
     break;
   }
+  case TargetOpcode::G_JUMP_TABLE: {
+    if (!MI->getOperand(1).isJTI())
+      report("G_JUMP_TABLE source operand must be a jump table index", MI);
+    LLT DstTy = MRI->getType(MI->getOperand(0).getReg());
+    if (!DstTy.isPointer())
+      report("G_JUMP_TABLE dest operand must have a pointer type", MI);
+    break;
+  }
   default:
     break;
   }
 }
 
 void MachineVerifier::visitMachineInstrBefore(const MachineInstr *MI) {
   const MCInstrDesc &MCID = MI->getDesc();
   if (MI->getNumOperands() < MCID.getNumOperands()) {

llvm/test/MachineVerifier/test_g_jump_table.mir

+# RUN: not llc -march=aarch64 -o /dev/null -run-pass=none -verify-machineinstrs %s 2>&1 | FileCheck %s
+# REQUIRES: global-isel, aarch64-registered-target
+
+---
+name:            test_jump_table
+legalized:       true
+tracksRegLiveness: true
+jumpTable:
+  kind:            block-address
+  entries:
+    - id:              0
+      blocks:          [ '%bb.0' ]
+liveins:
+body:             |
+  bb.0:
+
+    ; CHECK: Bad machine code: Too few operands
+    %0:_(s32) = G_JUMP_TABLE
+
+    ; CHECK: G_JUMP_TABLE source operand must be a jump table index
+    %2:_(s32) = G_JUMP_TABLE %0
+
+    ; CHECK: G_JUMP_TABLE dest operand must have a pointer type
+    %3:_(s32) = G_JUMP_TABLE %jump-table.0
+
+...