[GlobalISel] Add a G_JUMP_TABLE opcode.

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.

Differential Revision: https://reviews.llvm.org/D63111

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@363096 91177308-0d34-0410-b5e6-96231b3b80d8

Author: aemerson

include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h

@@ -1359,6 +1359,14 @@ class MachineIRBuilder {
     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);

include/llvm/Support/TargetOpcodes.def

@@ -566,12 +566,15 @@ 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.

include/llvm/Target/GenericOpcodes.td

@@ -169,6 +169,12 @@ def G_BLOCK_ADDR : GenericInstruction {
   let hasSideEffects = 0;
 }
 
+def G_JUMP_TABLE : GenericInstruction {
+  let OutOperandList = (outs type0:$dst);
+  let InOperandList = (ins unknown:$jti);
+  let hasSideEffects = 0;
+}
+
 //------------------------------------------------------------------------------
 // Binary ops.
 //------------------------------------------------------------------------------

lib/CodeGen/GlobalISel/MachineIRBuilder.cpp

@@ -179,6 +179,12 @@ MachineInstrBuilder MachineIRBuilder::buildGlobalValue(unsigned 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");

lib/CodeGen/MachineVerifier.cpp

@@ -1312,6 +1312,14 @@ void MachineVerifier::verifyPreISelGenericInstruction(const MachineInstr *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;
   }

test/MachineVerifier/test_g_jump_table.mir

@@ -0,0 +1,26 @@
+# 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
+
+...