[IR] llvm.reloc.none intrinsic for no-op symbol references #147427
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@llvm/pr-subscribers-llvm-globalisel @llvm/pr-subscribers-llvm-ir Author: Daniel Thornburgh (mysterymath) ChangesThis intrinsic emits a BFD_RELOC_NONE relocation at the point of call, which allows optimizations and languages to explicitly pull in symbols from static libraries without there being any code or data that has an effectual relocation against such a symbol. See issue #146159 for context. Full diff: https://github.com/llvm/llvm-project/pull/147427.diff 10 Files Affected:
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index cc72a37f68599..187182e5357e7 100644
--- a/llvm/docs/LangRef.rst
+++ b/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.fake.use`` 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
--------------------
diff --git a/llvm/include/llvm/CodeGen/ISDOpcodes.h b/llvm/include/llvm/CodeGen/ISDOpcodes.h
index 465e4a0a9d0d8..9c36f9c4fe525 100644
--- a/llvm/include/llvm/CodeGen/ISDOpcodes.h
+++ b/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,
diff --git a/llvm/include/llvm/CodeGen/SelectionDAGISel.h b/llvm/include/llvm/CodeGen/SelectionDAGISel.h
index 375d2f31e2835..3a399c39c496f 100644
--- a/llvm/include/llvm/CodeGen/SelectionDAGISel.h
+++ b/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);
diff --git a/llvm/include/llvm/IR/Intrinsics.td b/llvm/include/llvm/IR/Intrinsics.td
index 7add4a27ce9e9..131bc56c32362 100644
--- a/llvm/include/llvm/IR/Intrinsics.td
+++ b/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<[],
diff --git a/llvm/include/llvm/Support/TargetOpcodes.def b/llvm/include/llvm/Support/TargetOpcodes.def
index 92fd60e03112a..5fd0b2a06188e 100644
--- a/llvm/include/llvm/Support/TargetOpcodes.def
+++ b/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)
diff --git a/llvm/include/llvm/Target/Target.td b/llvm/include/llvm/Target/Target.td
index ce9a2b2751968..fca69107c8b55 100644
--- a/llvm/include/llvm/Target/Target.td
+++ b/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 {
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index a2c3b50b24670..e6206e6cbb6ae 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/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);
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index c01f1e7928477..bcfbca582d699 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/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.
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp
index 7fc15581c17e4..5296913e718c2 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp
+++ b/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";
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 4b98d87fcc63b..ccc583c6a2b8d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/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;
|
|
Sending this out as a draft to obtain some early feedback about the direction of the implemenation of the Modular Printf RFC. Next PR in chain: #147429 |
This was referenced Jul 8, 2025
petrhosek
reviewed
Jul 8, 2025
arsenm
reviewed
Jul 8, 2025
arsenm
reviewed
Jul 26, 2025
Comment on lines
+7763
to
+7766
| auto *M = const_cast<Module *>(I.getModule()); | ||
| auto *RelocSymbol = cast<GlobalVariable>( | ||
| M->getOrInsertGlobal(SymbolName, StructType::create(M->getContext()))); |
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This is because this occurs in a MachineFunctionPass right? In that case, I got bamboozled! I had unceremoniously copy-pasted this from the lowering of Intrinsic::amdgcn_reloc_constant in SIISelLowering.cpp, which also runs in a MachineFunctionPass. I'll admit that this completely slipped past me, although I was curious about the const_cast.
AFAIK, converting an arbitrary symbol name metadata string to a GlobalValue reference instrinsically mutates the module. So, if we wanted to fix this, we could either go back to having this be a symbol reference to a pre-existing global value, or we could forward the metadata string to RELOC_NONE as a string (odd in the backend; unsure if this is even possible?) to be lowered to a symbol reference at assembly time. My preference would definitely be the former, since it has fewer unknowns.
Whichever we choose, also I'd think either way we should give amdgcn_reloc_constant the same treatment, unless it's not possible to do so for backwards compatibility reasons.
@arsenm Do you have preferences here?
EDIT: There is Metadata and MCSymbol support in MachineOperand, but it's tagged in the enum as "for debug info". We could probably use this for RELOC_NONE's argument, but maybe that would cause problems? (Or be "weird"?) Unsure.
llvmbot
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llvm:codegen
llvm:globalisel
llvm:support
llvm:SelectionDAG
This intrinsic emits a BFD_RELOC_NONE relocation at the point of call, which allows optimizations and languages to explicitly pull in symbols from static libraries without there being any code or data that has an effectual relocation against such a symbol. See issue #146159 for context.
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Alright, I've filled out tests and added lowering to GlobalISel also. This should be formally ready for review (although much has already occurred). |
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This intrinsic emits a BFD_RELOC_NONE relocation at the point of call, which allows optimizations and languages to explicitly pull in symbols from static libraries without there being any code or data that has an effectual relocation against such a symbol.
See issue #146159 for context.