llvm/llvm/lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp

//=== WebAssemblyLateEHPrepare.cpp - WebAssembly Exception Preparation -===//
//
// 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
/// \brief Does various transformations for exception handling.
///
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "WebAssembly.h"
#include "WebAssemblySubtarget.h"
#include "WebAssemblyUtilities.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/WasmEHFuncInfo.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetMachine.h"
usingnamespacellvm;

#define DEBUG_TYPE …

namespace {
class WebAssemblyLateEHPrepare final : public MachineFunctionPass { … };
} // end anonymous namespace

char WebAssemblyLateEHPrepare::ID = …;
INITIALIZE_PASS(…)

FunctionPass *llvm::createWebAssemblyLateEHPrepare() { … }

// Returns the nearest EH pad that dominates this instruction. This does not use
// dominator analysis; it just does BFS on its predecessors until arriving at an
// EH pad. This assumes valid EH scopes so the first EH pad it arrives in all
// possible search paths should be the same.
// Returns nullptr in case it does not find any EH pad in the search, or finds
// multiple different EH pads.
MachineBasicBlock *
WebAssemblyLateEHPrepare::getMatchingEHPad(MachineInstr *MI) { … }

// Erase the specified BBs if the BB does not have any remaining predecessors,
// and also all its dead children.
template <typename Container>
static void eraseDeadBBsAndChildren(const Container &MBBs) { … }

bool WebAssemblyLateEHPrepare::runOnMachineFunction(MachineFunction &MF) { … }

// Remove unreachable EH pads and its children. If they remain, CFG
// stackification can be tricky.
bool WebAssemblyLateEHPrepare::removeUnreachableEHPads(MachineFunction &MF) { … }

// Record which BB ends with catchret instruction, because this will be replaced
// with 'br's later. This set of catchret BBs is necessary in 'getMatchingEHPad'
// function.
void WebAssemblyLateEHPrepare::recordCatchRetBBs(MachineFunction &MF) { … }

// Hoist catch instructions to the beginning of their matching EH pad BBs in
// case,
// (1) catch instruction is not the first instruction in EH pad.
// ehpad:
//   some_other_instruction
//   ...
//   %exn = catch 0
// (2) catch instruction is in a non-EH pad BB. For example,
// ehpad:
//   br bb0
// bb0:
//   %exn = catch 0
bool WebAssemblyLateEHPrepare::hoistCatches(MachineFunction &MF) { … }

// Add catch_all to beginning of cleanup pads.
bool WebAssemblyLateEHPrepare::addCatchAlls(MachineFunction &MF) { … }

// Replace pseudo-instructions catchret and cleanupret with br and rethrow
// respectively.
bool WebAssemblyLateEHPrepare::replaceFuncletReturns(MachineFunction &MF) { … }

// Add CATCH_REF and CATCH_ALL_REF pseudo instructions to EH pads, and convert
// RETHROWs to THROW_REFs.
bool WebAssemblyLateEHPrepare::addCatchRefsAndThrowRefs(MachineFunction &MF) { … }

// Remove unnecessary unreachables after a throw/rethrow/throw_ref.
bool WebAssemblyLateEHPrepare::removeUnnecessaryUnreachables(
    MachineFunction &MF) { … }

// After the stack is unwound due to a thrown exception, the __stack_pointer
// global can point to an invalid address. This inserts instructions that
// restore __stack_pointer global.
bool WebAssemblyLateEHPrepare::restoreStackPointer(MachineFunction &MF) { … }