Coverage Report

Created: 2019-07-24 05:18

/Users/buildslave/jenkins/workspace/clang-stage2-coverage-R/llvm/lib/CodeGen/AsmPrinter/WasmException.cpp
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//===-- CodeGen/AsmPrinter/WasmException.cpp - Wasm Exception Impl --------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains support for writing WebAssembly exception info into asm
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// files.
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//
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//===----------------------------------------------------------------------===//
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#include "WasmException.h"
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#include "llvm/IR/Mangler.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCStreamer.h"
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using namespace llvm;
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void WasmException::endModule() {
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  // This is the symbol used in 'throw' and 'br_on_exn' instruction to denote
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  // this is a C++ exception. This symbol has to be emitted somewhere once in
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  // the module.  Check if the symbol has already been created, i.e., we have at
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  // least one 'throw' or 'br_on_exn' instruction in the module, and emit the
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  // symbol only if so.
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  SmallString<60> NameStr;
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  Mangler::getNameWithPrefix(NameStr, "__cpp_exception", Asm->getDataLayout());
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  if (Asm->OutContext.lookupSymbol(NameStr)) {
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    MCSymbol *ExceptionSym = Asm->GetExternalSymbolSymbol("__cpp_exception");
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    Asm->OutStreamer->EmitLabel(ExceptionSym);
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  }
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}
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void WasmException::markFunctionEnd() {
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  // Get rid of any dead landing pads.
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  if (!Asm->MF->getLandingPads().empty()) {
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    auto *NonConstMF = const_cast<MachineFunction *>(Asm->MF);
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    // Wasm does not set BeginLabel and EndLabel information for landing pads,
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    // so we should set the second argument false.
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    NonConstMF->tidyLandingPads(nullptr, /* TidyIfNoBeginLabels */ false);
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  }
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}
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void WasmException::endFunction(const MachineFunction *MF) {
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  bool ShouldEmitExceptionTable = false;
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  for (const LandingPadInfo &Info : MF->getLandingPads()) {
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    if (MF->hasWasmLandingPadIndex(Info.LandingPadBlock)) {
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      ShouldEmitExceptionTable = true;
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      break;
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    }
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  }
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  if (!ShouldEmitExceptionTable)
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    return;
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  MCSymbol *LSDALabel = emitExceptionTable();
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  assert(LSDALabel && ".GCC_exception_table has not been emitted!");
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  // Wasm requires every data section symbol to have a .size set. So we emit an
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  // end marker and set the size as the difference between the start end the end
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  // marker.
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  MCSymbol *LSDAEndLabel = Asm->createTempSymbol("GCC_except_table_end");
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  Asm->OutStreamer->EmitLabel(LSDAEndLabel);
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  MCContext &OutContext = Asm->OutStreamer->getContext();
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  const MCExpr *SizeExp = MCBinaryExpr::createSub(
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      MCSymbolRefExpr::create(LSDAEndLabel, OutContext),
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      MCSymbolRefExpr::create(LSDALabel, OutContext), OutContext);
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  Asm->OutStreamer->emitELFSize(LSDALabel, SizeExp);
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}
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// Compute the call-site table for wasm EH. Even though we use the same function
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// name to share the common routines, a call site entry in the table corresponds
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// to not a call site for possibly-throwing functions but a landing pad. In wasm
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// EH the VM is responsible for stack unwinding. After an exception occurs and
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// the stack is unwound, the control flow is transferred to wasm 'catch'
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// instruction by the VM, after which the personality function is called from
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// the compiler-generated code. Refer to WasmEHPrepare pass for more
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// information.
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void WasmException::computeCallSiteTable(
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    SmallVectorImpl<CallSiteEntry> &CallSites,
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    const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
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    const SmallVectorImpl<unsigned> &FirstActions) {
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  MachineFunction &MF = *Asm->MF;
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  for (unsigned I = 0, N = LandingPads.size(); I < N; 
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) {
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    const LandingPadInfo *Info = LandingPads[I];
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    MachineBasicBlock *LPad = Info->LandingPadBlock;
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    // We don't emit LSDA for single catch (...).
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    if (!MF.hasWasmLandingPadIndex(LPad))
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      continue;
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    // Wasm EH must maintain the EH pads in the order assigned to them by the
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    // WasmEHPrepare pass.
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    unsigned LPadIndex = MF.getWasmLandingPadIndex(LPad);
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    CallSiteEntry Site = {nullptr, nullptr, Info, FirstActions[I]};
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    if (CallSites.size() < LPadIndex + 1)
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      CallSites.resize(LPadIndex + 1);
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    CallSites[LPadIndex] = Site;
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  }
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}