[IR] llvm.reloc.none intrinsic for no-op symbol references

llvm/docs/LangRef.rst

@@ -30439,6 +30439,38 @@ This intrinsic does nothing, but optimizers must consider it a use of its single
 operand and should try to preserve the intrinsic and its position in the
 function.
 
+.. _llvm_reloc_none:
+
+'``llvm.reloc.none``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare void @llvm.reloc.none(ptrty %ptr)
+
+Overview:
+"""""""""
+
+The ``llvm.reloc.none`` intrinsic emits a no-op relocation against a given
+operand symbol. This can bring the symbol
+definition into the link without emitting any code or data to the binary for
+that purpose.
+
+Arguments:
+""""""""""
+
+The ``llvm.reloc.none`` intrinsic takes one argument, which may be any global
+value.
+
+Semantics:
+""""""""""
+
+This intrinsic emits a no-op relocation at the location of the intrinsic call
+for the symbol that corresponds to the global value argument.
+
 
 Stack Map Intrinsics
 --------------------

llvm/include/llvm/CodeGen/ISDOpcodes.h

@@ -1531,6 +1531,9 @@ enum NodeType {
 #define BEGIN_REGISTER_VP_SDNODE(VPSDID, ...) VPSDID,
 #include "llvm/IR/VPIntrinsics.def"
 
+  // Issue a no-op relocation against a given symbol at the current location.
+  RELOC_NONE,
+
   // The `llvm.experimental.convergence.*` intrinsics.
   CONVERGENCECTRL_ANCHOR,
   CONVERGENCECTRL_ENTRY,

llvm/include/llvm/CodeGen/SelectionDAGISel.h

@@ -473,6 +473,7 @@ class SelectionDAGISel {
   void Select_WRITE_REGISTER(SDNode *Op);
   void Select_UNDEF(SDNode *N);
   void Select_FAKE_USE(SDNode *N);
+  void Select_RELOC_NONE(SDNode *N);
   void CannotYetSelect(SDNode *N);
 
   void Select_FREEZE(SDNode *N);

llvm/include/llvm/IR/Intrinsics.td

@@ -1917,6 +1917,9 @@ def int_threadlocal_address : DefaultAttrsIntrinsic<[llvm_anyptr_ty], [LLVMMatch
 def int_stepvector : DefaultAttrsIntrinsic<[llvm_anyvector_ty],
                                             [], [IntrNoMem]>;
 
+def int_reloc_none : DefaultAttrsIntrinsic<[], [llvm_ptr_ty],
+  [IntrHasSideEffects, IntrInaccessibleMemOnly, IntrWillReturn]>;
+
 //===---------------- Vector Predication Intrinsics --------------===//
 // Memory Intrinsics
 def int_vp_store : DefaultAttrsIntrinsic<[],

llvm/include/llvm/Support/TargetOpcodes.def

@@ -233,6 +233,9 @@ HANDLE_TARGET_OPCODE(MEMBARRIER)
 // using.
 HANDLE_TARGET_OPCODE(JUMP_TABLE_DEBUG_INFO)
 
+// Issue a no-op relocation against a given symbol at the current location.
+HANDLE_TARGET_OPCODE(RELOC_NONE)
+
 HANDLE_TARGET_OPCODE(CONVERGENCECTRL_ENTRY)
 HANDLE_TARGET_OPCODE(CONVERGENCECTRL_ANCHOR)
 HANDLE_TARGET_OPCODE(CONVERGENCECTRL_LOOP)

llvm/include/llvm/Target/Target.td

@@ -1532,6 +1532,11 @@ def JUMP_TABLE_DEBUG_INFO : StandardPseudoInstruction {
   let Size = 0;
   let isMeta = true;
 }
+def RELOC_NONE : StandardPseudoInstruction {
+  let OutOperandList = (outs);
+  let InOperandList = (ins unknown:$symbol);
+  let hasSideEffects = true;
+}
 
 let hasSideEffects = false, isMeta = true, isConvergent = true in {
 def CONVERGENCECTRL_ANCHOR : StandardPseudoInstruction {

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -1930,6 +1930,20 @@ void AsmPrinter::emitFunctionBody() {
         // This is only used to influence register allocation behavior, no
         // actual initialization is needed.
         break;
+      case TargetOpcode::RELOC_NONE: {
+        // Generate a temporary label for the current PC.
+        MCSymbol *Sym = OutContext.createTempSymbol("reloc_none");
+        OutStreamer->emitLabel(Sym);
+        const MCExpr *Dot = MCSymbolRefExpr::create(Sym, OutContext);
+
+        assert(MI.getNumOperands() == 1 &&
+               "RELOC_NONE can only have one operand");
+        const MCExpr *Value = MCSymbolRefExpr::create(
+            getSymbol(MI.getOperand(0).getGlobal()), OutContext);
+        OutStreamer->emitRelocDirective(*Dot, "BFD_RELOC_NONE", Value, SMLoc(),
+                                        *STI);
+        break;
+      }
       default:
         emitInstruction(&MI);
 

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -7757,6 +7757,19 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
     return;
   }
 
+  case Intrinsic::reloc_none: {
+    SDValue V = getValue(I.getArgOperand(0));
+    auto *GA = dyn_cast<GlobalAddressSDNode>(V);
+    if (!GA)
+      report_fatal_error("llvm.reloc.none operand must be a GlobalValue");
+    SDValue Ops[2];
+    Ops[0] = getRoot();
+    Ops[1] = DAG.getTargetGlobalAddress(GA->getGlobal(), sdl, V.getValueType(),
+                                        GA->getOffset());
+    DAG.setRoot(DAG.getNode(ISD::RELOC_NONE, sdl, MVT::Other, Ops));
+    return;
+  }
+
   case Intrinsic::eh_exceptionpointer:
   case Intrinsic::eh_exceptioncode: {
     // Get the exception pointer vreg, copy from it, and resize it to fit.

llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp

@@ -471,6 +471,8 @@ std::string SDNode::getOperationName(const SelectionDAG *G) const {
   case ISD::LIFETIME_END:               return "lifetime.end";
   case ISD::FAKE_USE:
     return "fake_use";
+  case ISD::RELOC_NONE:
+    return "reloc_none";
   case ISD::PSEUDO_PROBE:
     return "pseudoprobe";
   case ISD::GC_TRANSITION_START:        return "gc_transition.start";

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -2498,6 +2498,11 @@ void SelectionDAGISel::Select_FAKE_USE(SDNode *N) {
                        N->getOperand(1), N->getOperand(0));
 }
 
+void SelectionDAGISel::Select_RELOC_NONE(SDNode *N) {
+  CurDAG->SelectNodeTo(N, TargetOpcode::RELOC_NONE, N->getValueType(0),
+                       N->getOperand(1), N->getOperand(0));
+}
+
 void SelectionDAGISel::Select_FREEZE(SDNode *N) {
   // TODO: We don't have FREEZE pseudo-instruction in MachineInstr-level now.
   // If FREEZE instruction is added later, the code below must be changed as
@@ -3273,6 +3278,9 @@ void SelectionDAGISel::SelectCodeCommon(SDNode *NodeToMatch,
   case ISD::FAKE_USE:
     Select_FAKE_USE(NodeToMatch);
     return;
+  case ISD::RELOC_NONE:
+    Select_RELOC_NONE(NodeToMatch);
+    return;
   case ISD::FREEZE:
     Select_FREEZE(NodeToMatch);
     return;