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//===-- WebAssemblyUtilities.cpp - WebAssembly Utility Functions ----------===//
//
// 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 implements several utility functions for WebAssembly.
///
//===----------------------------------------------------------------------===//
#include "WebAssemblyUtilities.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/MC/MCContext.h"
using namespace llvm;
// Exception handling & setjmp-longjmp handling related options. These are
// defined here to be shared between WebAssembly and its subdirectories.
// Emscripten's asm.js-style exception handling
cl::opt<bool> WebAssembly::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> WebAssembly::WasmEnableEmSjLj(
"enable-emscripten-sjlj",
cl::desc("WebAssembly Emscripten-style setjmp/longjmp handling"),
cl::init(false));
// Exception handling using wasm EH instructions
cl::opt<bool>
WebAssembly::WasmEnableEH("wasm-enable-eh",
cl::desc("WebAssembly exception handling"),
cl::init(false));
// setjmp/longjmp handling using wasm EH instrutions
cl::opt<bool>
WebAssembly::WasmEnableSjLj("wasm-enable-sjlj",
cl::desc("WebAssembly setjmp/longjmp handling"),
cl::init(false));
// Function names in libc++abi and libunwind
const char *const WebAssembly::CxaBeginCatchFn = "__cxa_begin_catch";
const char *const WebAssembly::CxaRethrowFn = "__cxa_rethrow";
const char *const WebAssembly::StdTerminateFn = "_ZSt9terminatev";
const char *const WebAssembly::PersonalityWrapperFn =
"_Unwind_Wasm_CallPersonality";
/// Test whether MI is a child of some other node in an expression tree.
bool WebAssembly::isChild(const MachineInstr &MI,
const WebAssemblyFunctionInfo &MFI) {
if (MI.getNumOperands() == 0)
return false;
const MachineOperand &MO = MI.getOperand(0);
if (!MO.isReg() || MO.isImplicit() || !MO.isDef())
return false;
Register Reg = MO.getReg();
return Register::isVirtualRegister(Reg) && MFI.isVRegStackified(Reg);
}
bool WebAssembly::mayThrow(const MachineInstr &MI) {
switch (MI.getOpcode()) {
case WebAssembly::THROW:
case WebAssembly::THROW_S:
case WebAssembly::RETHROW:
case WebAssembly::RETHROW_S:
return true;
}
if (isCallIndirect(MI.getOpcode()))
return true;
if (!MI.isCall())
return false;
const MachineOperand &MO = getCalleeOp(MI);
assert(MO.isGlobal() || MO.isSymbol());
if (MO.isSymbol()) {
// Some intrinsics are lowered to calls to external symbols, which are then
// lowered to calls to library functions. Most of libcalls don't throw, but
// we only list some of them here now.
// TODO Consider adding 'nounwind' info in TargetLowering::CallLoweringInfo
// instead for more accurate info.
const char *Name = MO.getSymbolName();
if (strcmp(Name, "memcpy") == 0 || strcmp(Name, "memmove") == 0 ||
strcmp(Name, "memset") == 0)
return false;
return true;
}
const auto *F = dyn_cast<Function>(MO.getGlobal());
if (!F)
return true;
if (F->doesNotThrow())
return false;
// These functions never throw
if (F->getName() == CxaBeginCatchFn || F->getName() == PersonalityWrapperFn ||
F->getName() == StdTerminateFn)
return false;
// TODO Can we exclude call instructions that are marked as 'nounwind' in the
// original LLVm IR? (Even when the callee may throw)
return true;
}
const MachineOperand &WebAssembly::getCalleeOp(const MachineInstr &MI) {
switch (MI.getOpcode()) {
case WebAssembly::CALL:
case WebAssembly::CALL_S:
case WebAssembly::RET_CALL:
case WebAssembly::RET_CALL_S:
return MI.getOperand(MI.getNumExplicitDefs());
case WebAssembly::CALL_INDIRECT:
case WebAssembly::CALL_INDIRECT_S:
case WebAssembly::RET_CALL_INDIRECT:
case WebAssembly::RET_CALL_INDIRECT_S:
return MI.getOperand(MI.getNumExplicitOperands() - 1);
default:
llvm_unreachable("Not a call instruction");
}
}
MCSymbolWasm *WebAssembly::getOrCreateFunctionTableSymbol(
MCContext &Ctx, const WebAssemblySubtarget *Subtarget) {
StringRef Name = "__indirect_function_table";
MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(Name));
if (Sym) {
if (!Sym->isFunctionTable())
Ctx.reportError(SMLoc(), "symbol is not a wasm funcref table");
} else {
Sym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(Name));
Sym->setFunctionTable();
// The default function table is synthesized by the linker.
Sym->setUndefined();
}
// MVP object files can't have symtab entries for tables.
if (!(Subtarget && Subtarget->hasReferenceTypes()))
Sym->setOmitFromLinkingSection();
return Sym;
}
MCSymbolWasm *WebAssembly::getOrCreateFuncrefCallTableSymbol(
MCContext &Ctx, const WebAssemblySubtarget *Subtarget) {
StringRef Name = "__funcref_call_table";
MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(Name));
if (Sym) {
if (!Sym->isFunctionTable())
Ctx.reportError(SMLoc(), "symbol is not a wasm funcref table");
} else {
Sym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(Name));
// Setting Weak ensure only one table is left after linking when multiple
// modules define the table.
Sym->setWeak(true);
wasm::WasmLimits Limits = {0, 1, 1};
wasm::WasmTableType TableType = {wasm::WASM_TYPE_FUNCREF, Limits};
Sym->setType(wasm::WASM_SYMBOL_TYPE_TABLE);
Sym->setTableType(TableType);
}
// MVP object files can't have symtab entries for tables.
if (!(Subtarget && Subtarget->hasReferenceTypes()))
Sym->setOmitFromLinkingSection();
return Sym;
}
// Find a catch instruction from an EH pad.
MachineInstr *WebAssembly::findCatch(MachineBasicBlock *EHPad) {
assert(EHPad->isEHPad());
auto Pos = EHPad->begin();
// Skip any label or debug instructions. Also skip 'end' marker instructions
// that may exist after marker placement in CFGStackify.
while (Pos != EHPad->end() &&
(Pos->isLabel() || Pos->isDebugInstr() || isMarker(Pos->getOpcode())))
Pos++;
if (Pos != EHPad->end() && WebAssembly::isCatch(Pos->getOpcode()))
return &*Pos;
return nullptr;
}
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