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//===- WebAssemblyTargetMachine.cpp - Define TargetMachine 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 the WebAssembly-specific subclass of TargetMachine.
///
//===----------------------------------------------------------------------===//
#include "WebAssemblyTargetMachine.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "TargetInfo/WebAssemblyTargetInfo.h"
#include "WebAssembly.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "WebAssemblyTargetObjectFile.h"
#include "WebAssemblyTargetTransformInfo.h"
#include "llvm/CodeGen/MIRParser/MIParser.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/TargetRegistry.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/LowerAtomic.h"
#include "llvm/Transforms/Utils.h"
using namespace llvm;
#define DEBUG_TYPE "wasm"
// Emscripten's asm.js-style exception handling
cl::opt<bool>
WasmEnableEmEH("enable-emscripten-cxx-exceptions",
cl::desc("WebAssembly Emscripten-style exception handling"),
cl::init(false));
// Emscripten's asm.js-style setjmp/longjmp handling
cl::opt<bool> WasmEnableEmSjLj(
"enable-emscripten-sjlj",
cl::desc("WebAssembly Emscripten-style setjmp/longjmp handling"),
cl::init(false));
// Exception handling using wasm EH instructions
cl::opt<bool> WasmEnableEH("wasm-enable-eh",
cl::desc("WebAssembly exception handling"),
cl::init(false));
// setjmp/longjmp handling using wasm EH instrutions
cl::opt<bool> WasmEnableSjLj("wasm-enable-sjlj",
cl::desc("WebAssembly setjmp/longjmp handling"),
cl::init(false));
// A command-line option to keep implicit locals
// for the purpose of testing with lit/llc ONLY.
// This produces output which is not valid WebAssembly, and is not supported
// by assemblers/disassemblers and other MC based tools.
static cl::opt<bool> WasmDisableExplicitLocals(
"wasm-disable-explicit-locals", cl::Hidden,
cl::desc("WebAssembly: output implicit locals in"
" instruction output for test purposes only."),
cl::init(false));
extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeWebAssemblyTarget() {
// Register the target.
RegisterTargetMachine<WebAssemblyTargetMachine> X(
getTheWebAssemblyTarget32());
RegisterTargetMachine<WebAssemblyTargetMachine> Y(
getTheWebAssemblyTarget64());
// Register backend passes
auto &PR = *PassRegistry::getPassRegistry();
initializeWebAssemblyAddMissingPrototypesPass(PR);
initializeWebAssemblyLowerEmscriptenEHSjLjPass(PR);
initializeLowerGlobalDtorsPass(PR);
initializeFixFunctionBitcastsPass(PR);
initializeOptimizeReturnedPass(PR);
initializeWebAssemblyArgumentMovePass(PR);
initializeWebAssemblySetP2AlignOperandsPass(PR);
initializeWebAssemblyReplacePhysRegsPass(PR);
initializeWebAssemblyPrepareForLiveIntervalsPass(PR);
initializeWebAssemblyOptimizeLiveIntervalsPass(PR);
initializeWebAssemblyMemIntrinsicResultsPass(PR);
initializeWebAssemblyRegStackifyPass(PR);
initializeWebAssemblyRegColoringPass(PR);
initializeWebAssemblyNullifyDebugValueListsPass(PR);
initializeWebAssemblyFixIrreducibleControlFlowPass(PR);
initializeWebAssemblyLateEHPreparePass(PR);
initializeWebAssemblyExceptionInfoPass(PR);
initializeWebAssemblyCFGSortPass(PR);
initializeWebAssemblyCFGStackifyPass(PR);
initializeWebAssemblyExplicitLocalsPass(PR);
initializeWebAssemblyLowerBrUnlessPass(PR);
initializeWebAssemblyRegNumberingPass(PR);
initializeWebAssemblyDebugFixupPass(PR);
initializeWebAssemblyPeepholePass(PR);
initializeWebAssemblyMCLowerPrePassPass(PR);
}
//===----------------------------------------------------------------------===//
// WebAssembly Lowering public interface.
//===----------------------------------------------------------------------===//
static Reloc::Model getEffectiveRelocModel(Optional<Reloc::Model> RM,
const Triple &TT) {
if (!RM.hasValue()) {
// Default to static relocation model. This should always be more optimial
// than PIC since the static linker can determine all global addresses and
// assume direct function calls.
return Reloc::Static;
}
if (!TT.isOSEmscripten()) {
// Relocation modes other than static are currently implemented in a way
// that only works for Emscripten, so disable them if we aren't targeting
// Emscripten.
return Reloc::Static;
}
return *RM;
}
/// Create an WebAssembly architecture model.
///
WebAssemblyTargetMachine::WebAssemblyTargetMachine(
const Target &T, const Triple &TT, StringRef CPU, StringRef FS,
const TargetOptions &Options, Optional<Reloc::Model> RM,
Optional<CodeModel::Model> CM, CodeGenOpt::Level OL, bool JIT)
: LLVMTargetMachine(
T,
TT.isArch64Bit()
? (TT.isOSEmscripten() ? "e-m:e-p:64:64-p10:8:8-p20:8:8-i64:64-"
"f128:64-n32:64-S128-ni:1:10:20"
: "e-m:e-p:64:64-p10:8:8-p20:8:8-i64:64-"
"n32:64-S128-ni:1:10:20")
: (TT.isOSEmscripten() ? "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-"
"f128:64-n32:64-S128-ni:1:10:20"
: "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-"
"n32:64-S128-ni:1:10:20"),
TT, CPU, FS, Options, getEffectiveRelocModel(RM, TT),
getEffectiveCodeModel(CM, CodeModel::Large), OL),
TLOF(new WebAssemblyTargetObjectFile()) {
// WebAssembly type-checks instructions, but a noreturn function with a return
// type that doesn't match the context will cause a check failure. So we lower
// LLVM 'unreachable' to ISD::TRAP and then lower that to WebAssembly's
// 'unreachable' instructions which is meant for that case.
this->Options.TrapUnreachable = true;
// WebAssembly treats each function as an independent unit. Force
// -ffunction-sections, effectively, so that we can emit them independently.
this->Options.FunctionSections = true;
this->Options.DataSections = true;
this->Options.UniqueSectionNames = true;
initAsmInfo();
// Note that we don't use setRequiresStructuredCFG(true). It disables
// optimizations than we're ok with, and want, such as critical edge
// splitting and tail merging.
}
WebAssemblyTargetMachine::~WebAssemblyTargetMachine() = default; // anchor.
const WebAssemblySubtarget *WebAssemblyTargetMachine::getSubtargetImpl() const {
return getSubtargetImpl(std::string(getTargetCPU()),
std::string(getTargetFeatureString()));
}
const WebAssemblySubtarget *
WebAssemblyTargetMachine::getSubtargetImpl(std::string CPU,
std::string FS) const {
auto &I = SubtargetMap[CPU + FS];
if (!I) {
I = std::make_unique<WebAssemblySubtarget>(TargetTriple, CPU, FS, *this);
}
return I.get();
}
const WebAssemblySubtarget *
WebAssemblyTargetMachine::getSubtargetImpl(const Function &F) const {
Attribute CPUAttr = F.getFnAttribute("target-cpu");
Attribute FSAttr = F.getFnAttribute("target-features");
std::string CPU =
CPUAttr.isValid() ? CPUAttr.getValueAsString().str() : TargetCPU;
std::string FS =
FSAttr.isValid() ? FSAttr.getValueAsString().str() : TargetFS;
// This needs to be done before we create a new subtarget since any
// creation will depend on the TM and the code generation flags on the
// function that reside in TargetOptions.
resetTargetOptions(F);
return getSubtargetImpl(CPU, FS);
}
namespace {
class CoalesceFeaturesAndStripAtomics final : public ModulePass {
// Take the union of all features used in the module and use it for each
// function individually, since having multiple feature sets in one module
// currently does not make sense for WebAssembly. If atomics are not enabled,
// also strip atomic operations and thread local storage.
static char ID;
WebAssemblyTargetMachine *WasmTM;
public:
CoalesceFeaturesAndStripAtomics(WebAssemblyTargetMachine *WasmTM)
: ModulePass(ID), WasmTM(WasmTM) {}
bool runOnModule(Module &M) override {
FeatureBitset Features = coalesceFeatures(M);
std::string FeatureStr = getFeatureString(Features);
WasmTM->setTargetFeatureString(FeatureStr);
for (auto &F : M)
replaceFeatures(F, FeatureStr);
bool StrippedAtomics = false;
bool StrippedTLS = false;
if (!Features[WebAssembly::FeatureAtomics])
StrippedAtomics = stripAtomics(M);
if (!Features[WebAssembly::FeatureBulkMemory])
StrippedTLS = stripThreadLocals(M);
if (StrippedAtomics && !StrippedTLS)
stripThreadLocals(M);
else if (StrippedTLS && !StrippedAtomics)
stripAtomics(M);
recordFeatures(M, Features, StrippedAtomics || StrippedTLS);
// Conservatively assume we have made some change
return true;
}
private:
FeatureBitset coalesceFeatures(const Module &M) {
FeatureBitset Features =
WasmTM
->getSubtargetImpl(std::string(WasmTM->getTargetCPU()),
std::string(WasmTM->getTargetFeatureString()))
->getFeatureBits();
for (auto &F : M)
Features |= WasmTM->getSubtargetImpl(F)->getFeatureBits();
return Features;
}
std::string getFeatureString(const FeatureBitset &Features) {
std::string Ret;
for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
if (Features[KV.Value])
Ret += (StringRef("+") + KV.Key + ",").str();
}
return Ret;
}
void replaceFeatures(Function &F, const std::string &Features) {
F.removeFnAttr("target-features");
F.removeFnAttr("target-cpu");
F.addFnAttr("target-features", Features);
}
bool stripAtomics(Module &M) {
// Detect whether any atomics will be lowered, since there is no way to tell
// whether the LowerAtomic pass lowers e.g. stores.
bool Stripped = false;
for (auto &F : M) {
for (auto &B : F) {
for (auto &I : B) {
if (I.isAtomic()) {
Stripped = true;
goto done;
}
}
}
}
done:
if (!Stripped)
return false;
LowerAtomicPass Lowerer;
FunctionAnalysisManager FAM;
for (auto &F : M)
Lowerer.run(F, FAM);
return true;
}
bool stripThreadLocals(Module &M) {
bool Stripped = false;
for (auto &GV : M.globals()) {
if (GV.isThreadLocal()) {
Stripped = true;
GV.setThreadLocal(false);
}
}
return Stripped;
}
void recordFeatures(Module &M, const FeatureBitset &Features, bool Stripped) {
for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
if (Features[KV.Value]) {
// Mark features as used
std::string MDKey = (StringRef("wasm-feature-") + KV.Key).str();
M.addModuleFlag(Module::ModFlagBehavior::Error, MDKey,
wasm::WASM_FEATURE_PREFIX_USED);
}
}
// Code compiled without atomics or bulk-memory may have had its atomics or
// thread-local data lowered to nonatomic operations or non-thread-local
// data. In that case, we mark the pseudo-feature "shared-mem" as disallowed
// to tell the linker that it would be unsafe to allow this code ot be used
// in a module with shared memory.
if (Stripped) {
M.addModuleFlag(Module::ModFlagBehavior::Error, "wasm-feature-shared-mem",
wasm::WASM_FEATURE_PREFIX_DISALLOWED);
}
}
};
char CoalesceFeaturesAndStripAtomics::ID = 0;
/// WebAssembly Code Generator Pass Configuration Options.
class WebAssemblyPassConfig final : public TargetPassConfig {
public:
WebAssemblyPassConfig(WebAssemblyTargetMachine &TM, PassManagerBase &PM)
: TargetPassConfig(TM, PM) {}
WebAssemblyTargetMachine &getWebAssemblyTargetMachine() const {
return getTM<WebAssemblyTargetMachine>();
}
FunctionPass *createTargetRegisterAllocator(bool) override;
void addIRPasses() override;
bool addInstSelector() override;
void addPostRegAlloc() override;
bool addGCPasses() override { return false; }
void addPreEmitPass() override;
bool addPreISel() override;
// No reg alloc
bool addRegAssignAndRewriteFast() override { return false; }
// No reg alloc
bool addRegAssignAndRewriteOptimized() override { return false; }
};
} // end anonymous namespace
TargetTransformInfo
WebAssemblyTargetMachine::getTargetTransformInfo(const Function &F) {
return TargetTransformInfo(WebAssemblyTTIImpl(this, F));
}
TargetPassConfig *
WebAssemblyTargetMachine::createPassConfig(PassManagerBase &PM) {
return new WebAssemblyPassConfig(*this, PM);
}
FunctionPass *WebAssemblyPassConfig::createTargetRegisterAllocator(bool) {
return nullptr; // No reg alloc
}
static void basicCheckForEHAndSjLj(const TargetMachine *TM) {
// Basic Correctness checking related to -exception-model
if (TM->Options.ExceptionModel != ExceptionHandling::None &&
TM->Options.ExceptionModel != ExceptionHandling::Wasm)
report_fatal_error("-exception-model should be either 'none' or 'wasm'");
if (WasmEnableEmEH && TM->Options.ExceptionModel == ExceptionHandling::Wasm)
report_fatal_error("-exception-model=wasm not allowed with "
"-enable-emscripten-cxx-exceptions");
if (WasmEnableEH && TM->Options.ExceptionModel != ExceptionHandling::Wasm)
report_fatal_error(
"-wasm-enable-eh only allowed with -exception-model=wasm");
if (WasmEnableSjLj && TM->Options.ExceptionModel != ExceptionHandling::Wasm)
report_fatal_error(
"-wasm-enable-sjlj only allowed with -exception-model=wasm");
if ((!WasmEnableEH && !WasmEnableSjLj) &&
TM->Options.ExceptionModel == ExceptionHandling::Wasm)
report_fatal_error(
"-exception-model=wasm only allowed with at least one of "
"-wasm-enable-eh or -wasm-enable-sjj");
// You can't enable two modes of EH at the same time
if (WasmEnableEmEH && WasmEnableEH)
report_fatal_error(
"-enable-emscripten-cxx-exceptions not allowed with -wasm-enable-eh");
// You can't enable two modes of SjLj at the same time
if (WasmEnableEmSjLj && WasmEnableSjLj)
report_fatal_error(
"-enable-emscripten-sjlj not allowed with -wasm-enable-sjlj");
// You can't mix Emscripten EH with Wasm SjLj.
if (WasmEnableEmEH && WasmEnableSjLj)
report_fatal_error(
"-enable-emscripten-cxx-exceptions not allowed with -wasm-enable-sjlj");
// Currently it is allowed to mix Wasm EH with Emscripten SjLj as an interim
// measure, but some code will error out at compile time in this combination.
// See WebAssemblyLowerEmscriptenEHSjLj pass for details.
}
//===----------------------------------------------------------------------===//
// The following functions are called from lib/CodeGen/Passes.cpp to modify
// the CodeGen pass sequence.
//===----------------------------------------------------------------------===//
void WebAssemblyPassConfig::addIRPasses() {
// Lower atomics and TLS if necessary
addPass(new CoalesceFeaturesAndStripAtomics(&getWebAssemblyTargetMachine()));
// This is a no-op if atomics are not used in the module
addPass(createAtomicExpandPass());
// Add signatures to prototype-less function declarations
addPass(createWebAssemblyAddMissingPrototypes());
// Lower .llvm.global_dtors into .llvm_global_ctors with __cxa_atexit calls.
addPass(createWebAssemblyLowerGlobalDtors());
// Fix function bitcasts, as WebAssembly requires caller and callee signatures
// to match.
addPass(createWebAssemblyFixFunctionBitcasts());
// Optimize "returned" function attributes.
if (getOptLevel() != CodeGenOpt::None)
addPass(createWebAssemblyOptimizeReturned());
basicCheckForEHAndSjLj(TM);
// If exception handling is not enabled and setjmp/longjmp handling is
// enabled, we lower invokes into calls and delete unreachable landingpad
// blocks. Lowering invokes when there is no EH support is done in
// TargetPassConfig::addPassesToHandleExceptions, but that runs after these IR
// passes and Emscripten SjLj handling expects all invokes to be lowered
// before.
if (!WasmEnableEmEH && !WasmEnableEH) {
addPass(createLowerInvokePass());
// The lower invoke pass may create unreachable code. Remove it in order not
// to process dead blocks in setjmp/longjmp handling.
addPass(createUnreachableBlockEliminationPass());
}
// Handle exceptions and setjmp/longjmp if enabled. Unlike Wasm EH preparation
// done in WasmEHPrepare pass, Wasm SjLj preparation shares libraries and
// transformation algorithms with Emscripten SjLj, so we run
// LowerEmscriptenEHSjLj pass also when Wasm SjLj is enabled.
if (WasmEnableEmEH || WasmEnableEmSjLj || WasmEnableSjLj)
addPass(createWebAssemblyLowerEmscriptenEHSjLj());
// Expand indirectbr instructions to switches.
addPass(createIndirectBrExpandPass());
TargetPassConfig::addIRPasses();
}
bool WebAssemblyPassConfig::addInstSelector() {
(void)TargetPassConfig::addInstSelector();
addPass(
createWebAssemblyISelDag(getWebAssemblyTargetMachine(), getOptLevel()));
// Run the argument-move pass immediately after the ScheduleDAG scheduler
// so that we can fix up the ARGUMENT instructions before anything else
// sees them in the wrong place.
addPass(createWebAssemblyArgumentMove());
// Set the p2align operands. This information is present during ISel, however
// it's inconvenient to collect. Collect it now, and update the immediate
// operands.
addPass(createWebAssemblySetP2AlignOperands());
// Eliminate range checks and add default targets to br_table instructions.
addPass(createWebAssemblyFixBrTableDefaults());
return false;
}
void WebAssemblyPassConfig::addPostRegAlloc() {
// TODO: The following CodeGen passes don't currently support code containing
// virtual registers. Consider removing their restrictions and re-enabling
// them.
// These functions all require the NoVRegs property.
disablePass(&MachineCopyPropagationID);
disablePass(&PostRAMachineSinkingID);
disablePass(&PostRASchedulerID);
disablePass(&FuncletLayoutID);
disablePass(&StackMapLivenessID);
disablePass(&LiveDebugValuesID);
disablePass(&PatchableFunctionID);
disablePass(&ShrinkWrapID);
// This pass hurts code size for wasm because it can generate irreducible
// control flow.
disablePass(&MachineBlockPlacementID);
TargetPassConfig::addPostRegAlloc();
}
void WebAssemblyPassConfig::addPreEmitPass() {
TargetPassConfig::addPreEmitPass();
// Nullify DBG_VALUE_LISTs that we cannot handle.
addPass(createWebAssemblyNullifyDebugValueLists());
// Eliminate multiple-entry loops.
addPass(createWebAssemblyFixIrreducibleControlFlow());
// Do various transformations for exception handling.
// Every CFG-changing optimizations should come before this.
if (TM->Options.ExceptionModel == ExceptionHandling::Wasm)
addPass(createWebAssemblyLateEHPrepare());
// Now that we have a prologue and epilogue and all frame indices are
// rewritten, eliminate SP and FP. This allows them to be stackified,
// colored, and numbered with the rest of the registers.
addPass(createWebAssemblyReplacePhysRegs());
// Preparations and optimizations related to register stackification.
if (getOptLevel() != CodeGenOpt::None) {
// LiveIntervals isn't commonly run this late. Re-establish preconditions.
addPass(createWebAssemblyPrepareForLiveIntervals());
// Depend on LiveIntervals and perform some optimizations on it.
addPass(createWebAssemblyOptimizeLiveIntervals());
// Prepare memory intrinsic calls for register stackifying.
addPass(createWebAssemblyMemIntrinsicResults());
// Mark registers as representing wasm's value stack. This is a key
// code-compression technique in WebAssembly. We run this pass (and
// MemIntrinsicResults above) very late, so that it sees as much code as
// possible, including code emitted by PEI and expanded by late tail
// duplication.
addPass(createWebAssemblyRegStackify());
// Run the register coloring pass to reduce the total number of registers.
// This runs after stackification so that it doesn't consider registers
// that become stackified.
addPass(createWebAssemblyRegColoring());
}
// Sort the blocks of the CFG into topological order, a prerequisite for
// BLOCK and LOOP markers.
addPass(createWebAssemblyCFGSort());
// Insert BLOCK and LOOP markers.
addPass(createWebAssemblyCFGStackify());
// Insert explicit local.get and local.set operators.
if (!WasmDisableExplicitLocals)
addPass(createWebAssemblyExplicitLocals());
// Lower br_unless into br_if.
addPass(createWebAssemblyLowerBrUnless());
// Perform the very last peephole optimizations on the code.
if (getOptLevel() != CodeGenOpt::None)
addPass(createWebAssemblyPeephole());
// Create a mapping from LLVM CodeGen virtual registers to wasm registers.
addPass(createWebAssemblyRegNumbering());
// Fix debug_values whose defs have been stackified.
if (!WasmDisableExplicitLocals)
addPass(createWebAssemblyDebugFixup());
// Collect information to prepare for MC lowering / asm printing.
addPass(createWebAssemblyMCLowerPrePass());
}
bool WebAssemblyPassConfig::addPreISel() {
TargetPassConfig::addPreISel();
addPass(createWebAssemblyLowerRefTypesIntPtrConv());
return false;
}
yaml::MachineFunctionInfo *
WebAssemblyTargetMachine::createDefaultFuncInfoYAML() const {
return new yaml::WebAssemblyFunctionInfo();
}
yaml::MachineFunctionInfo *WebAssemblyTargetMachine::convertFuncInfoToYAML(
const MachineFunction &MF) const {
const auto *MFI = MF.getInfo<WebAssemblyFunctionInfo>();
return new yaml::WebAssemblyFunctionInfo(*MFI);
}
bool WebAssemblyTargetMachine::parseMachineFunctionInfo(
const yaml::MachineFunctionInfo &MFI, PerFunctionMIParsingState &PFS,
SMDiagnostic &Error, SMRange &SourceRange) const {
const auto &YamlMFI =
reinterpret_cast<const yaml::WebAssemblyFunctionInfo &>(MFI);
MachineFunction &MF = PFS.MF;
MF.getInfo<WebAssemblyFunctionInfo>()->initializeBaseYamlFields(YamlMFI);
return false;
}