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//===-- WebAssemblyEHRestoreStackPointer.cpp - __stack_pointer restoration ===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// 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.
///
//===----------------------------------------------------------------------===//
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "WebAssembly.h"
#include "WebAssemblySubtarget.h"
#include "WebAssemblyUtilities.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/MC/MCAsmInfo.h"
using namespace llvm;
#define DEBUG_TYPE "wasm-eh-restore-stack-pointer"
namespace {
class WebAssemblyEHRestoreStackPointer final : public MachineFunctionPass {
public:
static char ID; // Pass identification, replacement for typeid
WebAssemblyEHRestoreStackPointer() : MachineFunctionPass(ID) {}
StringRef getPassName() const override {
return "WebAssembly Restore Stack Pointer for Exception Handling";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
bool runOnMachineFunction(MachineFunction &MF) override;
};
} // end anonymous namespace
char WebAssemblyEHRestoreStackPointer::ID = 0;
INITIALIZE_PASS(WebAssemblyEHRestoreStackPointer, DEBUG_TYPE,
"Restore Stack Pointer for Exception Handling", true, false)
FunctionPass *llvm::createWebAssemblyEHRestoreStackPointer() {
return new WebAssemblyEHRestoreStackPointer();
}
bool WebAssemblyEHRestoreStackPointer::runOnMachineFunction(
MachineFunction &MF) {
const auto *FrameLowering = static_cast<const WebAssemblyFrameLowering *>(
MF.getSubtarget().getFrameLowering());
if (!FrameLowering->needsPrologForEH(MF))
return false;
bool Changed = false;
for (auto &MBB : MF) {
if (!MBB.isEHPad())
continue;
Changed = true;
// Insert __stack_pointer restoring instructions at the beginning of each EH
// pad, after the catch instruction. (Catch instructions may have been
// reordered, and catch_all instructions have not been inserted yet, but
// those cases are handled in LateEHPrepare).
//
// Here it is safe to assume that SP32 holds the latest value of
// __stack_pointer, because the only exception for this case is when a
// function uses the red zone, but that only happens with leaf functions,
// and we don't restore __stack_pointer in leaf functions anyway.
auto InsertPos = MBB.begin();
if (WebAssembly::isCatch(*MBB.begin()))
InsertPos++;
FrameLowering->writeSPToGlobal(WebAssembly::SP32, MF, MBB, InsertPos,
MBB.begin()->getDebugLoc());
}
return Changed;
}
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