src/llvm-project/llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp - toolchain/rustc - Git at Google

 //- WebAssemblyISelDAGToDAG.cpp - A dag to dag inst selector for WebAssembly -//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
 /// This file defines an instruction selector for the WebAssembly target.
 ///
 //===----------------------------------------------------------------------===//

 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
 #include "WebAssembly.h"
 #include "WebAssemblyTargetMachine.h"
 #include "llvm/CodeGen/SelectionDAGISel.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Function.h" // To access function attributes.
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;

 #define DEBUG_TYPE "wasm-isel"

 //===--------------------------------------------------------------------===//
 /// WebAssembly-specific code to select WebAssembly machine instructions for
 /// SelectionDAG operations.
 ///
 namespace {
 class WebAssemblyDAGToDAGISel final : public SelectionDAGISel {
   /// Keep a pointer to the WebAssemblySubtarget around so that we can make the
   /// right decision when generating code for different targets.
   const WebAssemblySubtarget *Subtarget;

   bool ForCodeSize;

 public:
   WebAssemblyDAGToDAGISel(WebAssemblyTargetMachine &TM,
                           CodeGenOpt::Level OptLevel)
       : SelectionDAGISel(TM, OptLevel), Subtarget(nullptr), ForCodeSize(false) {
   }

   StringRef getPassName() const override {
     return "WebAssembly Instruction Selection";
   }

   bool runOnMachineFunction(MachineFunction &MF) override {
     LLVM_DEBUG(dbgs() << "********** ISelDAGToDAG **********\n"
                          "********** Function: "
                       << MF.getName() << '\n');

     ForCodeSize = MF.getFunction().hasOptSize();
     Subtarget = &MF.getSubtarget<WebAssemblySubtarget>();
     return SelectionDAGISel::runOnMachineFunction(MF);
   }

   void Select(SDNode *Node) override;

   bool SelectInlineAsmMemoryOperand(const SDValue &Op, unsigned ConstraintID,
                                     std::vector<SDValue> &OutOps) override;

 // Include the pieces autogenerated from the target description.
 #include "WebAssemblyGenDAGISel.inc"

 private:
   // add select functions here...
 };
 } // end anonymous namespace

 void WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
   // If we have a custom node, we already have selected!
   if (Node->isMachineOpcode()) {
     LLVM_DEBUG(errs() << "== "; Node->dump(CurDAG); errs() << "\n");
     Node->setNodeId(-1);
     return;
   }

   // Few custom selection stuff.
   SDLoc DL(Node);
   MachineFunction &MF = CurDAG->getMachineFunction();
   switch (Node->getOpcode()) {
   case ISD::ATOMIC_FENCE: {
     if (!MF.getSubtarget<WebAssemblySubtarget>().hasAtomics())
       break;

     uint64_t SyncScopeID =
         cast<ConstantSDNode>(Node->getOperand(2).getNode())->getZExtValue();
     switch (SyncScopeID) {
     case SyncScope::SingleThread: {
       // We lower a single-thread fence to a pseudo compiler barrier instruction
       // preventing instruction reordering. This will not be emitted in final
       // binary.
       MachineSDNode *Fence =
           CurDAG->getMachineNode(WebAssembly::COMPILER_FENCE,
                                  DL,                 // debug loc
                                  MVT::Other,         // outchain type
                                  Node->getOperand(0) // inchain
           );
       ReplaceNode(Node, Fence);
       CurDAG->RemoveDeadNode(Node);
       return;
     }

     case SyncScope::System: {
       // For non-emscripten systems, we have not decided on what we should
       // traslate fences to yet.
       if (!Subtarget->getTargetTriple().isOSEmscripten())
         report_fatal_error(
             "ATOMIC_FENCE is not yet supported in non-emscripten OSes");

       // Wasm does not have a fence instruction, but because all atomic
       // instructions in wasm are sequentially consistent, we translate a
       // fence to an idempotent atomic RMW instruction to a linear memory
       // address. All atomic instructions in wasm are sequentially consistent,
       // but this is to ensure a fence also prevents reordering of non-atomic
       // instructions in the VM. Even though LLVM IR's fence instruction does
       // not say anything about its relationship with non-atomic instructions,
       // we think this is more user-friendly.
       //
       // While any address can work, here we use a value stored in
       // __stack_pointer wasm global because there's high chance that area is
       // in cache.
       //
       // So the selected instructions will be in the form of:
       //   %addr = get_global $__stack_pointer
       //   %0 = i32.const 0
       //   i32.atomic.rmw.or %addr, %0
       SDValue StackPtrSym = CurDAG->getTargetExternalSymbol(
           "__stack_pointer", TLI->getPointerTy(CurDAG->getDataLayout()));
       MachineSDNode *GetGlobal =
           CurDAG->getMachineNode(WebAssembly::GLOBAL_GET_I32, // opcode
                                  DL,                          // debug loc
                                  MVT::i32,                    // result type
                                  StackPtrSym // __stack_pointer symbol
           );

       SDValue Zero = CurDAG->getTargetConstant(0, DL, MVT::i32);
       auto *MMO = MF.getMachineMemOperand(
           MachinePointerInfo::getUnknownStack(MF),
           // FIXME Volatile isn't really correct, but currently all LLVM
           // atomic instructions are treated as volatiles in the backend, so
           // we should be consistent.
           MachineMemOperand::MOVolatile | MachineMemOperand::MOLoad |
               MachineMemOperand::MOStore,
           4, 4, AAMDNodes(), nullptr, SyncScope::System,
           AtomicOrdering::SequentiallyConsistent);
       MachineSDNode *Const0 =
           CurDAG->getMachineNode(WebAssembly::CONST_I32, DL, MVT::i32, Zero);
       MachineSDNode *AtomicRMW = CurDAG->getMachineNode(
           WebAssembly::ATOMIC_RMW_OR_I32, // opcode
           DL,                             // debug loc
           MVT::i32,                       // result type
           MVT::Other,                     // outchain type
           {
               Zero,                  // alignment
               Zero,                  // offset
               SDValue(GetGlobal, 0), // __stack_pointer
               SDValue(Const0, 0),    // OR with 0 to make it idempotent
               Node->getOperand(0)    // inchain
           });

       CurDAG->setNodeMemRefs(AtomicRMW, {MMO});
       ReplaceUses(SDValue(Node, 0), SDValue(AtomicRMW, 1));
       CurDAG->RemoveDeadNode(Node);
       return;
     }
     default:
       llvm_unreachable("Unknown scope!");
     }
   }

   case ISD::GlobalTLSAddress: {
     const auto *GA = cast<GlobalAddressSDNode>(Node);

     if (!MF.getSubtarget<WebAssemblySubtarget>().hasBulkMemory())
       report_fatal_error("cannot use thread-local storage without bulk memory",
                          false);

     // Currently Emscripten does not support dynamic linking with threads.
     // Therefore, if we have thread-local storage, only the local-exec model
     // is possible.
     // TODO: remove this and implement proper TLS models once Emscripten
     // supports dynamic linking with threads.
     if (GA->getGlobal()->getThreadLocalMode() !=
             GlobalValue::LocalExecTLSModel &&
         !Subtarget->getTargetTriple().isOSEmscripten()) {
       report_fatal_error("only -ftls-model=local-exec is supported for now on "
                          "non-Emscripten OSes: variable " +
                              GA->getGlobal()->getName(),
                          false);
     }

     MVT PtrVT = TLI->getPointerTy(CurDAG->getDataLayout());
     assert(PtrVT == MVT::i32 && "only wasm32 is supported for now");

     SDValue TLSBaseSym = CurDAG->getTargetExternalSymbol("__tls_base", PtrVT);
     SDValue TLSOffsetSym = CurDAG->getTargetGlobalAddress(
         GA->getGlobal(), DL, PtrVT, GA->getOffset(), 0);

     MachineSDNode *TLSBase = CurDAG->getMachineNode(WebAssembly::GLOBAL_GET_I32,
                                                     DL, MVT::i32, TLSBaseSym);
     MachineSDNode *TLSOffset = CurDAG->getMachineNode(
         WebAssembly::CONST_I32, DL, MVT::i32, TLSOffsetSym);
     MachineSDNode *TLSAddress =
         CurDAG->getMachineNode(WebAssembly::ADD_I32, DL, MVT::i32,
                                SDValue(TLSBase, 0), SDValue(TLSOffset, 0));
     ReplaceNode(Node, TLSAddress);
     return;
   }

   case ISD::INTRINSIC_WO_CHAIN: {
     unsigned IntNo = cast<ConstantSDNode>(Node->getOperand(0))->getZExtValue();
     switch (IntNo) {
     case Intrinsic::wasm_tls_size: {
       MVT PtrVT = TLI->getPointerTy(CurDAG->getDataLayout());
       assert(PtrVT == MVT::i32 && "only wasm32 is supported for now");

       MachineSDNode *TLSSize = CurDAG->getMachineNode(
           WebAssembly::GLOBAL_GET_I32, DL, PtrVT,
           CurDAG->getTargetExternalSymbol("__tls_size", MVT::i32));
       ReplaceNode(Node, TLSSize);
       return;
     }
     }
     break;
   }

   default:
     break;
   }

   // Select the default instruction.
   SelectCode(Node);
 }

 bool WebAssemblyDAGToDAGISel::SelectInlineAsmMemoryOperand(
     const SDValue &Op, unsigned ConstraintID, std::vector<SDValue> &OutOps) {
   switch (ConstraintID) {
   case InlineAsm::Constraint_i:
   case InlineAsm::Constraint_m:
     // We just support simple memory operands that just have a single address
     // operand and need no special handling.
     OutOps.push_back(Op);
     return false;
   default:
     break;
   }

   return true;
 }

 /// This pass converts a legalized DAG into a WebAssembly-specific DAG, ready
 /// for instruction scheduling.
 FunctionPass *llvm::createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
                                              CodeGenOpt::Level OptLevel) {
   return new WebAssemblyDAGToDAGISel(TM, OptLevel);
 }
	//- WebAssemblyISelDAGToDAG.cpp - A dag to dag inst selector for WebAssembly -//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//
	///
	/// \file
	/// This file defines an instruction selector for the WebAssembly target.
	///
	//===----------------------------------------------------------------------===//

	#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
	#include "WebAssembly.h"
	#include "WebAssemblyTargetMachine.h"
	#include "llvm/CodeGen/SelectionDAGISel.h"
	#include "llvm/IR/DiagnosticInfo.h"
	#include "llvm/IR/Function.h" // To access function attributes.
	#include "llvm/Support/Debug.h"
	#include "llvm/Support/KnownBits.h"
	#include "llvm/Support/MathExtras.h"
	#include "llvm/Support/raw_ostream.h"
	using namespace llvm;

	#define DEBUG_TYPE "wasm-isel"

	//===--------------------------------------------------------------------===//
	/// WebAssembly-specific code to select WebAssembly machine instructions for
	/// SelectionDAG operations.
	///
	namespace {
	class WebAssemblyDAGToDAGISel final : public SelectionDAGISel {
	/// Keep a pointer to the WebAssemblySubtarget around so that we can make the
	/// right decision when generating code for different targets.
	const WebAssemblySubtarget *Subtarget;

	bool ForCodeSize;

	public:
	WebAssemblyDAGToDAGISel(WebAssemblyTargetMachine &TM,
	CodeGenOpt::Level OptLevel)
	: SelectionDAGISel(TM, OptLevel), Subtarget(nullptr), ForCodeSize(false) {
	}

	StringRef getPassName() const override {
	return "WebAssembly Instruction Selection";
	}

	bool runOnMachineFunction(MachineFunction &MF) override {
	LLVM_DEBUG(dbgs() << "******** ISelDAGToDAG ********\n"
	"********** Function: "
	<< MF.getName() << '\n');

	ForCodeSize = MF.getFunction().hasOptSize();
	Subtarget = &MF.getSubtarget<WebAssemblySubtarget>();
	return SelectionDAGISel::runOnMachineFunction(MF);
	}

	void Select(SDNode *Node) override;

	bool SelectInlineAsmMemoryOperand(const SDValue &Op, unsigned ConstraintID,
	std::vector<SDValue> &OutOps) override;

	// Include the pieces autogenerated from the target description.
	#include "WebAssemblyGenDAGISel.inc"

	private:
	// add select functions here...
	};
	} // end anonymous namespace

	void WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
	// If we have a custom node, we already have selected!
	if (Node->isMachineOpcode()) {
	LLVM_DEBUG(errs() << "== "; Node->dump(CurDAG); errs() << "\n");
	Node->setNodeId(-1);
	return;
	}

	// Few custom selection stuff.
	SDLoc DL(Node);
	MachineFunction &MF = CurDAG->getMachineFunction();
	switch (Node->getOpcode()) {
	case ISD::ATOMIC_FENCE: {
	if (!MF.getSubtarget<WebAssemblySubtarget>().hasAtomics())
	break;

	uint64_t SyncScopeID =
	cast<ConstantSDNode>(Node->getOperand(2).getNode())->getZExtValue();
	switch (SyncScopeID) {
	case SyncScope::SingleThread: {
	// We lower a single-thread fence to a pseudo compiler barrier instruction
	// preventing instruction reordering. This will not be emitted in final
	// binary.
	MachineSDNode *Fence =
	CurDAG->getMachineNode(WebAssembly::COMPILER_FENCE,
	DL, // debug loc
	MVT::Other, // outchain type
	Node->getOperand(0) // inchain
	);
	ReplaceNode(Node, Fence);
	CurDAG->RemoveDeadNode(Node);
	return;
	}

	case SyncScope::System: {
	// For non-emscripten systems, we have not decided on what we should
	// traslate fences to yet.
	if (!Subtarget->getTargetTriple().isOSEmscripten())
	report_fatal_error(
	"ATOMIC_FENCE is not yet supported in non-emscripten OSes");

	// Wasm does not have a fence instruction, but because all atomic
	// instructions in wasm are sequentially consistent, we translate a
	// fence to an idempotent atomic RMW instruction to a linear memory
	// address. All atomic instructions in wasm are sequentially consistent,
	// but this is to ensure a fence also prevents reordering of non-atomic
	// instructions in the VM. Even though LLVM IR's fence instruction does
	// not say anything about its relationship with non-atomic instructions,
	// we think this is more user-friendly.
	//
	// While any address can work, here we use a value stored in
	// __stack_pointer wasm global because there's high chance that area is
	// in cache.
	//
	// So the selected instructions will be in the form of:
	// %addr = get_global $__stack_pointer
	// %0 = i32.const 0
	// i32.atomic.rmw.or %addr, %0
	SDValue StackPtrSym = CurDAG->getTargetExternalSymbol(
	"__stack_pointer", TLI->getPointerTy(CurDAG->getDataLayout()));
	MachineSDNode *GetGlobal =
	CurDAG->getMachineNode(WebAssembly::GLOBAL_GET_I32, // opcode
	DL, // debug loc
	MVT::i32, // result type
	StackPtrSym // __stack_pointer symbol
	);

	SDValue Zero = CurDAG->getTargetConstant(0, DL, MVT::i32);
	auto *MMO = MF.getMachineMemOperand(
	MachinePointerInfo::getUnknownStack(MF),
	// FIXME Volatile isn't really correct, but currently all LLVM
	// atomic instructions are treated as volatiles in the backend, so
	// we should be consistent.
	MachineMemOperand::MOVolatile \| MachineMemOperand::MOLoad \|
	MachineMemOperand::MOStore,
	4, 4, AAMDNodes(), nullptr, SyncScope::System,
	AtomicOrdering::SequentiallyConsistent);
	MachineSDNode *Const0 =
	CurDAG->getMachineNode(WebAssembly::CONST_I32, DL, MVT::i32, Zero);
	MachineSDNode *AtomicRMW = CurDAG->getMachineNode(
	WebAssembly::ATOMIC_RMW_OR_I32, // opcode
	DL, // debug loc
	MVT::i32, // result type
	MVT::Other, // outchain type
	{
	Zero, // alignment
	Zero, // offset
	SDValue(GetGlobal, 0), // __stack_pointer
	SDValue(Const0, 0), // OR with 0 to make it idempotent
	Node->getOperand(0) // inchain
	});

	CurDAG->setNodeMemRefs(AtomicRMW, {MMO});
	ReplaceUses(SDValue(Node, 0), SDValue(AtomicRMW, 1));
	CurDAG->RemoveDeadNode(Node);
	return;
	}
	default:
	llvm_unreachable("Unknown scope!");
	}
	}

	case ISD::GlobalTLSAddress: {
	const auto *GA = cast<GlobalAddressSDNode>(Node);

	if (!MF.getSubtarget<WebAssemblySubtarget>().hasBulkMemory())
	report_fatal_error("cannot use thread-local storage without bulk memory",
	false);

	// Currently Emscripten does not support dynamic linking with threads.
	// Therefore, if we have thread-local storage, only the local-exec model
	// is possible.
	// TODO: remove this and implement proper TLS models once Emscripten
	// supports dynamic linking with threads.
	if (GA->getGlobal()->getThreadLocalMode() !=
	GlobalValue::LocalExecTLSModel &&
	!Subtarget->getTargetTriple().isOSEmscripten()) {
	report_fatal_error("only -ftls-model=local-exec is supported for now on "
	"non-Emscripten OSes: variable " +
	GA->getGlobal()->getName(),
	false);
	}

	MVT PtrVT = TLI->getPointerTy(CurDAG->getDataLayout());
	assert(PtrVT == MVT::i32 && "only wasm32 is supported for now");

	SDValue TLSBaseSym = CurDAG->getTargetExternalSymbol("__tls_base", PtrVT);
	SDValue TLSOffsetSym = CurDAG->getTargetGlobalAddress(
	GA->getGlobal(), DL, PtrVT, GA->getOffset(), 0);

	MachineSDNode *TLSBase = CurDAG->getMachineNode(WebAssembly::GLOBAL_GET_I32,
	DL, MVT::i32, TLSBaseSym);
	MachineSDNode *TLSOffset = CurDAG->getMachineNode(
	WebAssembly::CONST_I32, DL, MVT::i32, TLSOffsetSym);
	MachineSDNode *TLSAddress =
	CurDAG->getMachineNode(WebAssembly::ADD_I32, DL, MVT::i32,
	SDValue(TLSBase, 0), SDValue(TLSOffset, 0));
	ReplaceNode(Node, TLSAddress);
	return;
	}

	case ISD::INTRINSIC_WO_CHAIN: {
	unsigned IntNo = cast<ConstantSDNode>(Node->getOperand(0))->getZExtValue();
	switch (IntNo) {
	case Intrinsic::wasm_tls_size: {
	MVT PtrVT = TLI->getPointerTy(CurDAG->getDataLayout());
	assert(PtrVT == MVT::i32 && "only wasm32 is supported for now");

	MachineSDNode *TLSSize = CurDAG->getMachineNode(
	WebAssembly::GLOBAL_GET_I32, DL, PtrVT,
	CurDAG->getTargetExternalSymbol("__tls_size", MVT::i32));
	ReplaceNode(Node, TLSSize);
	return;
	}
	}
	break;
	}

	default:
	break;
	}

	// Select the default instruction.
	SelectCode(Node);
	}

	bool WebAssemblyDAGToDAGISel::SelectInlineAsmMemoryOperand(
	const SDValue &Op, unsigned ConstraintID, std::vector<SDValue> &OutOps) {
	switch (ConstraintID) {
	case InlineAsm::Constraint_i:
	case InlineAsm::Constraint_m:
	// We just support simple memory operands that just have a single address
	// operand and need no special handling.
	OutOps.push_back(Op);
	return false;
	default:
	break;
	}

	return true;
	}

	/// This pass converts a legalized DAG into a WebAssembly-specific DAG, ready
	/// for instruction scheduling.
	FunctionPass *llvm::createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
	CodeGenOpt::Level OptLevel) {
	return new WebAssemblyDAGToDAGISel(TM, OptLevel);
	}