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archived-llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
Thomas Lively 39812314f7 [WebAssembly] Target features section 
Summary:
Implements a new target features section in assembly and object files
that records what features are used, required, and disallowed in
WebAssembly objects. The linker uses this information to ensure that
all objects participating in a link are feature-compatible and records
the set of used features in the output binary for use by optimizers
and other tools later in the toolchain.

The "atomics" feature is always required or disallowed to prevent
linking code with stripped atomics into multithreaded binaries. Other
features are marked used if they are enabled globally or on any
function in a module.

Future CLs will add linker flags for ignoring feature compatibility
checks and for specifying the set of allowed features, implement using
the presence of the "atomics" feature to control the type of memory
and segments in the linked binary, and add front-end flags for
relaxing the linkage policy for atomics.

Reviewers: aheejin, sbc100, dschuff

Subscribers: jgravelle-google, hiraditya, sunfish, mgrang, jfb, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59173

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356610 91177308-0d34-0410-b5e6-96231b3b80d8
2019-03-20 20:26:45 +00:00

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//===-- WebAssemblyAsmPrinter.cpp - WebAssembly LLVM assembly writer ------===//
//
// 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 contains a printer that converts from our internal
/// representation of machine-dependent LLVM code to the WebAssembly assembly
/// language.
///
//===----------------------------------------------------------------------===//
#include "WebAssemblyAsmPrinter.h"
#include "InstPrinter/WebAssemblyInstPrinter.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "MCTargetDesc/WebAssemblyTargetStreamer.h"
#include "WebAssembly.h"
#include "WebAssemblyMCInstLower.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "WebAssemblyRegisterInfo.h"
#include "WebAssemblyTargetMachine.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/BinaryFormat/Wasm.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineModuleInfoImpls.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCSectionWasm.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCSymbolWasm.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "asm-printer"
extern cl::opt<bool> WasmKeepRegisters;
//===----------------------------------------------------------------------===//
// Helpers.
//===----------------------------------------------------------------------===//
MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
MVT::v4i32, MVT::v2i64, MVT::v4f32, MVT::v2f64})
if (TRI->isTypeLegalForClass(*TRC, T))
return T;
LLVM_DEBUG(errs() << "Unknown type for register number: " << RegNo);
llvm_unreachable("Unknown register type");
return MVT::Other;
}
std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
unsigned RegNo = MO.getReg();
assert(TargetRegisterInfo::isVirtualRegister(RegNo) &&
"Unlowered physical register encountered during assembly printing");
assert(!MFI->isVRegStackified(RegNo));
unsigned WAReg = MFI->getWAReg(RegNo);
assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
return '$' + utostr(WAReg);
}
WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
return static_cast<WebAssemblyTargetStreamer *>(TS);
}
//===----------------------------------------------------------------------===//
// WebAssemblyAsmPrinter Implementation.
//===----------------------------------------------------------------------===//
void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
for (auto &It : OutContext.getSymbols()) {
// Emit a .globaltype and .eventtype declaration.
auto Sym = cast<MCSymbolWasm>(It.getValue());
if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_GLOBAL)
getTargetStreamer()->emitGlobalType(Sym);
else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_EVENT)
getTargetStreamer()->emitEventType(Sym);
}
for (const auto &F : M) {
// Emit function type info for all undefined functions
if (F.isDeclarationForLinker() && !F.isIntrinsic()) {
SmallVector<MVT, 4> Results;
SmallVector<MVT, 4> Params;
computeSignatureVTs(F.getFunctionType(), F, TM, Params, Results);
auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
Sym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
if (!Sym->getSignature()) {
auto Signature = signatureFromMVTs(Results, Params);
Sym->setSignature(Signature.get());
addSignature(std::move(Signature));
}
// FIXME: this was originally intended for post-linking and was only used
// for imports that were only called indirectly (i.e. s2wasm could not
// infer the type from a call). With object files it applies to all
// imports. so fix the names and the tests, or rethink how import
// delcarations work in asm files.
getTargetStreamer()->emitFunctionType(Sym);
if (TM.getTargetTriple().isOSBinFormatWasm() &&
F.hasFnAttribute("wasm-import-module")) {
StringRef Name =
F.getFnAttribute("wasm-import-module").getValueAsString();
Sym->setImportModule(Name);
getTargetStreamer()->emitImportModule(Sym, Name);
}
if (TM.getTargetTriple().isOSBinFormatWasm() &&
F.hasFnAttribute("wasm-import-name")) {
StringRef Name =
F.getFnAttribute("wasm-import-name").getValueAsString();
Sym->setImportName(Name);
getTargetStreamer()->emitImportName(Sym, Name);
}
}
}
for (const auto &G : M.globals()) {
if (!G.hasInitializer() && G.hasExternalLinkage()) {
if (G.getValueType()->isSized()) {
uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
OutStreamer->emitELFSize(getSymbol(&G),
MCConstantExpr::create(Size, OutContext));
}
}
}
if (const NamedMDNode *Named = M.getNamedMetadata("wasm.custom_sections")) {
for (const Metadata *MD : Named->operands()) {
const auto *Tuple = dyn_cast<MDTuple>(MD);
if (!Tuple || Tuple->getNumOperands() != 2)
continue;
const MDString *Name = dyn_cast<MDString>(Tuple->getOperand(0));
const MDString *Contents = dyn_cast<MDString>(Tuple->getOperand(1));
if (!Name || !Contents)
continue;
OutStreamer->PushSection();
std::string SectionName = (".custom_section." + Name->getString()).str();
MCSectionWasm *MySection =
OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
OutStreamer->SwitchSection(MySection);
OutStreamer->EmitBytes(Contents->getString());
OutStreamer->PopSection();
}
}
EmitProducerInfo(M);
EmitTargetFeatures();
}
void WebAssemblyAsmPrinter::EmitProducerInfo(Module &M) {
llvm::SmallVector<std::pair<std::string, std::string>, 4> Languages;
if (const NamedMDNode *Debug = M.getNamedMetadata("llvm.dbg.cu")) {
llvm::SmallSet<StringRef, 4> SeenLanguages;
for (size_t I = 0, E = Debug->getNumOperands(); I < E; ++I) {
const auto *CU = cast<DICompileUnit>(Debug->getOperand(I));
StringRef Language = dwarf::LanguageString(CU->getSourceLanguage());
Language.consume_front("DW_LANG_");
if (SeenLanguages.insert(Language).second)
Languages.emplace_back(Language.str(), "");
}
}
llvm::SmallVector<std::pair<std::string, std::string>, 4> Tools;
if (const NamedMDNode *Ident = M.getNamedMetadata("llvm.ident")) {
llvm::SmallSet<StringRef, 4> SeenTools;
for (size_t I = 0, E = Ident->getNumOperands(); I < E; ++I) {
const auto *S = cast<MDString>(Ident->getOperand(I)->getOperand(0));
std::pair<StringRef, StringRef> Field = S->getString().split("version");
StringRef Name = Field.first.trim();
StringRef Version = Field.second.trim();
if (SeenTools.insert(Name).second)
Tools.emplace_back(Name.str(), Version.str());
}
}
int FieldCount = int(!Languages.empty()) + int(!Tools.empty());
if (FieldCount != 0) {
MCSectionWasm *Producers = OutContext.getWasmSection(
".custom_section.producers", SectionKind::getMetadata());
OutStreamer->PushSection();
OutStreamer->SwitchSection(Producers);
OutStreamer->EmitULEB128IntValue(FieldCount);
for (auto &Producers : {std::make_pair("language", &Languages),
std::make_pair("processed-by", &Tools)}) {
if (Producers.second->empty())
continue;
OutStreamer->EmitULEB128IntValue(strlen(Producers.first));
OutStreamer->EmitBytes(Producers.first);
OutStreamer->EmitULEB128IntValue(Producers.second->size());
for (auto &Producer : *Producers.second) {
OutStreamer->EmitULEB128IntValue(Producer.first.size());
OutStreamer->EmitBytes(Producer.first);
OutStreamer->EmitULEB128IntValue(Producer.second.size());
OutStreamer->EmitBytes(Producer.second);
}
}
OutStreamer->PopSection();
}
}
void WebAssemblyAsmPrinter::EmitTargetFeatures() {
static const std::pair<unsigned, const char *> FeaturePairs[] = {
{WebAssembly::FeatureAtomics, "atomics"},
{WebAssembly::FeatureBulkMemory, "bulk-memory"},
{WebAssembly::FeatureExceptionHandling, "exception-handling"},
{WebAssembly::FeatureNontrappingFPToInt, "nontrapping-fptoint"},
{WebAssembly::FeatureSignExt, "sign-ext"},
{WebAssembly::FeatureSIMD128, "simd128"},
};
struct FeatureEntry {
uint8_t Prefix;
StringRef Name;
};
FeatureBitset UsedFeatures =
static_cast<WebAssemblyTargetMachine &>(TM).getUsedFeatures();
// Calculate the features and linkage policies to emit
SmallVector<FeatureEntry, 4> EmittedFeatures;
for (auto &F : FeaturePairs) {
FeatureEntry Entry;
Entry.Name = F.second;
if (F.first == WebAssembly::FeatureAtomics) {
// "atomics" is special: code compiled without atomics may have had its
// atomics lowered to nonatomic operations. Such code would be dangerous
// to mix with proper atomics, so it is always Required or Disallowed.
Entry.Prefix = UsedFeatures[F.first] ? wasm::WASM_FEATURE_PREFIX_REQUIRED
: wasm::WASM_FEATURE_PREFIX_DISALLOWED;
EmittedFeatures.push_back(Entry);
} else {
// Other features are marked Used or not mentioned
if (UsedFeatures[F.first]) {
Entry.Prefix = wasm::WASM_FEATURE_PREFIX_USED;
EmittedFeatures.push_back(Entry);
}
}
}
// Emit features and linkage policies into the "target_features" section
MCSectionWasm *FeaturesSection = OutContext.getWasmSection(
".custom_section.target_features", SectionKind::getMetadata());
OutStreamer->PushSection();
OutStreamer->SwitchSection(FeaturesSection);
OutStreamer->EmitULEB128IntValue(EmittedFeatures.size());
for (auto &F : EmittedFeatures) {
OutStreamer->EmitIntValue(F.Prefix, 1);
OutStreamer->EmitULEB128IntValue(F.Name.size());
OutStreamer->EmitBytes(F.Name);
}
OutStreamer->PopSection();
}
void WebAssemblyAsmPrinter::EmitConstantPool() {
assert(MF->getConstantPool()->getConstants().empty() &&
"WebAssembly disables constant pools");
}
void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
// Nothing to do; jump tables are incorporated into the instruction stream.
}
void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
const Function &F = MF->getFunction();
SmallVector<MVT, 1> ResultVTs;
SmallVector<MVT, 4> ParamVTs;
computeSignatureVTs(F.getFunctionType(), F, TM, ParamVTs, ResultVTs);
auto Signature = signatureFromMVTs(ResultVTs, ParamVTs);
auto *WasmSym = cast<MCSymbolWasm>(CurrentFnSym);
WasmSym->setSignature(Signature.get());
addSignature(std::move(Signature));
WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
// FIXME: clean up how params and results are emitted (use signatures)
getTargetStreamer()->emitFunctionType(WasmSym);
// Emit the function index.
if (MDNode *Idx = F.getMetadata("wasm.index")) {
assert(Idx->getNumOperands() == 1);
getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
}
SmallVector<wasm::ValType, 16> Locals;
valTypesFromMVTs(MFI->getLocals(), Locals);
getTargetStreamer()->emitLocal(Locals);
AsmPrinter::EmitFunctionBodyStart();
}
void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
switch (MI->getOpcode()) {
case WebAssembly::ARGUMENT_i32:
case WebAssembly::ARGUMENT_i32_S:
case WebAssembly::ARGUMENT_i64:
case WebAssembly::ARGUMENT_i64_S:
case WebAssembly::ARGUMENT_f32:
case WebAssembly::ARGUMENT_f32_S:
case WebAssembly::ARGUMENT_f64:
case WebAssembly::ARGUMENT_f64_S:
case WebAssembly::ARGUMENT_v16i8:
case WebAssembly::ARGUMENT_v16i8_S:
case WebAssembly::ARGUMENT_v8i16:
case WebAssembly::ARGUMENT_v8i16_S:
case WebAssembly::ARGUMENT_v4i32:
case WebAssembly::ARGUMENT_v4i32_S:
case WebAssembly::ARGUMENT_v2i64:
case WebAssembly::ARGUMENT_v2i64_S:
case WebAssembly::ARGUMENT_v4f32:
case WebAssembly::ARGUMENT_v4f32_S:
case WebAssembly::ARGUMENT_v2f64:
case WebAssembly::ARGUMENT_v2f64_S:
// These represent values which are live into the function entry, so there's
// no instruction to emit.
break;
case WebAssembly::FALLTHROUGH_RETURN_I32:
case WebAssembly::FALLTHROUGH_RETURN_I32_S:
case WebAssembly::FALLTHROUGH_RETURN_I64:
case WebAssembly::FALLTHROUGH_RETURN_I64_S:
case WebAssembly::FALLTHROUGH_RETURN_F32:
case WebAssembly::FALLTHROUGH_RETURN_F32_S:
case WebAssembly::FALLTHROUGH_RETURN_F64:
case WebAssembly::FALLTHROUGH_RETURN_F64_S:
case WebAssembly::FALLTHROUGH_RETURN_v16i8:
case WebAssembly::FALLTHROUGH_RETURN_v16i8_S:
case WebAssembly::FALLTHROUGH_RETURN_v8i16:
case WebAssembly::FALLTHROUGH_RETURN_v8i16_S:
case WebAssembly::FALLTHROUGH_RETURN_v4i32:
case WebAssembly::FALLTHROUGH_RETURN_v4i32_S:
case WebAssembly::FALLTHROUGH_RETURN_v2i64:
case WebAssembly::FALLTHROUGH_RETURN_v2i64_S:
case WebAssembly::FALLTHROUGH_RETURN_v4f32:
case WebAssembly::FALLTHROUGH_RETURN_v4f32_S:
case WebAssembly::FALLTHROUGH_RETURN_v2f64:
case WebAssembly::FALLTHROUGH_RETURN_v2f64_S: {
// These instructions represent the implicit return at the end of a
// function body. Always pops one value off the stack.
if (isVerbose()) {
OutStreamer->AddComment("fallthrough-return-value");
OutStreamer->AddBlankLine();
}
break;
}
case WebAssembly::FALLTHROUGH_RETURN_VOID:
case WebAssembly::FALLTHROUGH_RETURN_VOID_S:
// This instruction represents the implicit return at the end of a
// function body with no return value.
if (isVerbose()) {
OutStreamer->AddComment("fallthrough-return-void");
OutStreamer->AddBlankLine();
}
break;
case WebAssembly::EXTRACT_EXCEPTION_I32:
case WebAssembly::EXTRACT_EXCEPTION_I32_S:
// These are pseudo instructions that simulates popping values from stack.
// We print these only when we have -wasm-keep-registers on for assembly
// readability.
if (!WasmKeepRegisters)
break;
LLVM_FALLTHROUGH;
default: {
WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
MCInst TmpInst;
MCInstLowering.lower(MI, TmpInst);
EmitToStreamer(*OutStreamer, TmpInst);
break;
}
}
}
bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
unsigned OpNo, unsigned AsmVariant,
const char *ExtraCode,
raw_ostream &OS) {
if (AsmVariant != 0)
report_fatal_error("There are no defined alternate asm variants");
// First try the generic code, which knows about modifiers like 'c' and 'n'.
if (!AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, OS))
return false;
if (!ExtraCode) {
const MachineOperand &MO = MI->getOperand(OpNo);
switch (MO.getType()) {
case MachineOperand::MO_Immediate:
OS << MO.getImm();
return false;
case MachineOperand::MO_Register:
// FIXME: only opcode that still contains registers, as required by
// MachineInstr::getDebugVariable().
assert(MI->getOpcode() == WebAssembly::INLINEASM);
OS << regToString(MO);
return false;
case MachineOperand::MO_GlobalAddress:
getSymbol(MO.getGlobal())->print(OS, MAI);
printOffset(MO.getOffset(), OS);
return false;
case MachineOperand::MO_ExternalSymbol:
GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
printOffset(MO.getOffset(), OS);
return false;
case MachineOperand::MO_MachineBasicBlock:
MO.getMBB()->getSymbol()->print(OS, MAI);
return false;
default:
break;
}
}
return true;
}
bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
unsigned OpNo,
unsigned AsmVariant,
const char *ExtraCode,
raw_ostream &OS) {
if (AsmVariant != 0)
report_fatal_error("There are no defined alternate asm variants");
// The current approach to inline asm is that "r" constraints are expressed
// as local indices, rather than values on the operand stack. This simplifies
// using "r" as it eliminates the need to push and pop the values in a
// particular order, however it also makes it impossible to have an "m"
// constraint. So we don't support it.
return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, AsmVariant, ExtraCode, OS);
}
// Force static initialization.
extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
}
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