CIRGenCleanup.cpp

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//===--- CIRGenCleanup.cpp - Bookkeeping and code emission for cleanups ---===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file contains code dealing with the IR generation for cleanups
// and related information.
//
// A "cleanup" is a piece of code which needs to be executed whenever
// control transfers out of a particular scope.  This can be
// conditionalized to occur only on exceptional control flow, only on
// normal control flow, or both.
//
//===----------------------------------------------------------------------===//
 
#include "CIRGenCleanup.h"
#include "CIRGenFunction.h"
 
#include "clang/CIR/MissingFeatures.h"
 
using namespace clang;
using namespace clang::CIRGen;
 
//===----------------------------------------------------------------------===//
// CIRGenFunction cleanup related
//===----------------------------------------------------------------------===//
 
/// Emits all the code to cause the given temporary to be cleaned up.
void CIRGenFunction::emitCXXTemporary(const CXXTemporary *temporary,
                                      QualType tempType, Address ptr) {
  pushDestroy(NormalAndEHCleanup, ptr, tempType, destroyCXXObject);
}
 
//===----------------------------------------------------------------------===//
// EHScopeStack
//===----------------------------------------------------------------------===//
 
void EHScopeStack::Cleanup::anchor() {}
 
EHScopeStack::stable_iterator
EHScopeStack::getInnermostActiveNormalCleanup() const {
  stable_iterator si = getInnermostNormalCleanup();
  stable_iterator se = stable_end();
  while (si != se) {
    EHCleanupScope &cleanup = llvm::cast<EHCleanupScope>(*find(si));
    if (cleanup.isActive())
      return si;
    si = cleanup.getEnclosingNormalCleanup();
  }
  return stable_end();
}
 
/// Push an entry of the given size onto this protected-scope stack.
char *EHScopeStack::allocate(size_t size) {
  size = llvm::alignTo(size, ScopeStackAlignment);
  if (!startOfBuffer) {
    unsigned capacity = llvm::PowerOf2Ceil(std::max<size_t>(size, 1024ul));
    startOfBuffer = std::make_unique<char[]>(capacity);
    startOfData = endOfBuffer = startOfBuffer.get() + capacity;
  } else if (static_cast<size_t>(startOfData - startOfBuffer.get()) < size) {
    unsigned currentCapacity = endOfBuffer - startOfBuffer.get();
    unsigned usedCapacity =
        currentCapacity - (startOfData - startOfBuffer.get());
    unsigned requiredCapacity = usedCapacity + size;
    // We know from the 'else if' condition that requiredCapacity is greater
    // than currentCapacity.
    unsigned newCapacity = llvm::PowerOf2Ceil(requiredCapacity);
 
    std::unique_ptr<char[]> newStartOfBuffer =
        std::make_unique<char[]>(newCapacity);
    char *newEndOfBuffer = newStartOfBuffer.get() + newCapacity;
    char *newStartOfData = newEndOfBuffer - usedCapacity;
    memcpy(newStartOfData, startOfData, usedCapacity);
    startOfBuffer.swap(newStartOfBuffer);
    endOfBuffer = newEndOfBuffer;
    startOfData = newStartOfData;
  }
 
  assert(startOfBuffer.get() + size <= startOfData);
  startOfData -= size;
  return startOfData;
}
 
void EHScopeStack::deallocate(size_t size) {
  startOfData += llvm::alignTo(size, ScopeStackAlignment);
}
 
void *EHScopeStack::pushCleanup(CleanupKind kind, size_t size) {
  char *buffer = allocate(EHCleanupScope::getSizeForCleanupSize(size));
  bool isNormalCleanup = kind & NormalCleanup;
  bool isEHCleanup = kind & EHCleanup;
  bool isLifetimeMarker = kind & LifetimeMarker;
  bool skipCleanupScope = false;
 
  cir::CleanupKind cleanupKind = cir::CleanupKind::All;
  if (isEHCleanup && cgf->getLangOpts().Exceptions) {
    cleanupKind =
        isNormalCleanup ? cir::CleanupKind::All : cir::CleanupKind::EH;
  } else {
    if (isNormalCleanup)
      cleanupKind = cir::CleanupKind::Normal;
    else
      skipCleanupScope = true;
  }
 
  cir::CleanupScopeOp cleanupScope = nullptr;
  if (!skipCleanupScope) {
    CIRGenBuilderTy &builder = cgf->getBuilder();
    mlir::Location loc = builder.getUnknownLoc();
    cleanupScope = cir::CleanupScopeOp::create(
        builder, loc, cleanupKind,
        /*bodyBuilder=*/
        [&](mlir::OpBuilder &b, mlir::Location loc) {
          // Terminations will be handled in popCleanup
        },
        /*cleanupBuilder=*/
        [&](mlir::OpBuilder &b, mlir::Location loc) {
          // Terminations will be handled after emiting cleanup
        });
 
    builder.setInsertionPointToEnd(&cleanupScope.getBodyRegion().back());
  }
 
  // Per C++ [except.terminate], it is implementation-defined whether none,
  // some, or all cleanups are called before std::terminate. Thus, when
  // terminate is the current EH scope, we may skip adding any EH cleanup
  // scopes.
  if (innermostEHScope != stable_end() &&
      find(innermostEHScope)->getKind() == EHScope::Terminate)
    isEHCleanup = false;
 
  EHCleanupScope *scope = new (buffer)
      EHCleanupScope(isNormalCleanup, isEHCleanup, size, cleanupScope,
                     innermostNormalCleanup, innermostEHScope);
 
  if (isNormalCleanup)
    innermostNormalCleanup = stable_begin();
 
  if (isEHCleanup)
    innermostEHScope = stable_begin();
 
  if (isLifetimeMarker)
    cgf->cgm.errorNYI("push lifetime marker cleanup");
 
  // With Windows -EHa, Invoke llvm.seh.scope.begin() for EHCleanup
  if (cgf->getLangOpts().EHAsynch && isEHCleanup && !isLifetimeMarker &&
      cgf->getTarget().getCXXABI().isMicrosoft())
    cgf->cgm.errorNYI("push seh cleanup");
 
  return scope->getCleanupBuffer();
}
 
void EHScopeStack::popCleanup() {
  assert(!empty() && "popping exception stack when not empty");
 
  assert(isa<EHCleanupScope>(*begin()));
  EHCleanupScope &cleanup = cast<EHCleanupScope>(*begin());
  innermostNormalCleanup = cleanup.getEnclosingNormalCleanup();
  innermostEHScope = cleanup.getEnclosingEHScope();
  deallocate(cleanup.getAllocatedSize());
 
  cir::CleanupScopeOp cleanupScope = cleanup.getCleanupScopeOp();
  if (cleanupScope) {
    auto *block = &cleanupScope.getBodyRegion().back();
    if (!block->mightHaveTerminator()) {
      mlir::OpBuilder::InsertionGuard guard(cgf->getBuilder());
      cgf->getBuilder().setInsertionPointToEnd(block);
      cir::YieldOp::create(cgf->getBuilder(),
                           cgf->getBuilder().getUnknownLoc());
    }
    cgf->getBuilder().setInsertionPointAfter(cleanupScope);
  }
 
  // Destroy the cleanup.
  cleanup.destroy();
}
 
bool EHScopeStack::requiresCatchOrCleanup() const {
  for (stable_iterator si = getInnermostEHScope(); si != stable_end();) {
    if (auto *cleanup = dyn_cast<EHCleanupScope>(&*find(si))) {
      if (cleanup->isLifetimeMarker()) {
        // Skip lifetime markers and continue from the enclosing EH scope
        assert(!cir::MissingFeatures::emitLifetimeMarkers());
        continue;
      }
    }
    return true;
  }
  return false;
}
 
/// Deactive a cleanup that was created in an active state.
void CIRGenFunction::deactivateCleanupBlock(EHScopeStack::stable_iterator c,
                                            mlir::Operation *dominatingIP) {
  assert(c != ehStack.stable_end() && "deactivating bottom of stack?");
  EHCleanupScope &scope = cast<EHCleanupScope>(*ehStack.find(c));
  assert(scope.isActive() && "double deactivation");
 
  // If it's the top of the stack, just pop it, but do so only if it belongs
  // to the current RunCleanupsScope.
  if (c == ehStack.stable_begin() &&
      currentCleanupStackDepth.strictlyEncloses(c)) {
    popCleanupBlock();
    return;
  }
 
  // Otherwise, follow the general case.
  cgm.errorNYI("deactivateCleanupBlock: setupCleanupBlockActivation");
}
 
static void emitCleanup(CIRGenFunction &cgf, cir::CleanupScopeOp cleanupScope,
                        EHScopeStack::Cleanup *cleanup,
                        EHScopeStack::Cleanup::Flags flags) {
  CIRGenBuilderTy &builder = cgf.getBuilder();
  mlir::Block &block = cleanupScope.getCleanupRegion().back();
 
  mlir::OpBuilder::InsertionGuard guard(builder);
  builder.setInsertionPointToStart(&block);
 
  // Ask the cleanup to emit itself.
  assert(cgf.haveInsertPoint() && "expected insertion point");
  assert(!cir::MissingFeatures::ehCleanupActiveFlag());
  cleanup->emit(cgf, flags);
  assert(cgf.haveInsertPoint() && "cleanup ended with no insertion point?");
 
  mlir::Block &cleanupRegionLastBlock = cleanupScope.getCleanupRegion().back();
  if (cleanupRegionLastBlock.empty() ||
      !cleanupRegionLastBlock.back().hasTrait<mlir::OpTrait::IsTerminator>()) {
    mlir::OpBuilder::InsertionGuard guardCase(builder);
    builder.setInsertionPointToEnd(&cleanupRegionLastBlock);
    builder.createYield(cleanupScope.getLoc());
  }
}
 
static mlir::Block *createNormalEntry(CIRGenFunction &cgf,
                                      EHCleanupScope &scope) {
  assert(scope.isNormalCleanup());
  mlir::Block *entry = scope.getNormalBlock();
  if (!entry) {
    mlir::OpBuilder::InsertionGuard guard(cgf.getBuilder());
    entry = cgf.curLexScope->getOrCreateCleanupBlock(cgf.getBuilder());
    scope.setNormalBlock(entry);
  }
  return entry;
}
 
void CIRGenFunction::popCleanupBlock() {
  assert(!ehStack.empty() && "cleanup stack is empty!");
  assert(isa<EHCleanupScope>(*ehStack.begin()) && "top not a cleanup!");
  EHCleanupScope &scope = cast<EHCleanupScope>(*ehStack.begin());
 
  cir::CleanupScopeOp cleanupScope = scope.getCleanupScopeOp();
  assert(cleanupScope && "CleanupScopeOp is nullptr");
 
  // Remember activation information.
  bool isActive = scope.isActive();
 
  // - whether there's a fallthrough
  mlir::Block *fallthroughSource = builder.getInsertionBlock();
  bool hasFallthrough = fallthroughSource != nullptr && isActive;
 
  bool requiresNormalCleanup = scope.isNormalCleanup() && hasFallthrough;
  bool requiresEHCleanup = scope.isEHCleanup() && hasFallthrough;
 
  // If we don't need the cleanup at all, we're done.
  assert(!cir::MissingFeatures::ehCleanupScopeRequiresEHCleanup());
  if (!requiresNormalCleanup && !requiresEHCleanup) {
    ehStack.popCleanup();
    return;
  }
 
  // Copy the cleanup emission data out.  This uses either a stack
  // array or malloc'd memory, depending on the size, which is
  // behavior that SmallVector would provide, if we could use it
  // here. Unfortunately, if you ask for a SmallVector<char>, the
  // alignment isn't sufficient.
  auto *cleanupSource = reinterpret_cast<char *>(scope.getCleanupBuffer());
  alignas(EHScopeStack::ScopeStackAlignment) char
      cleanupBufferStack[8 * sizeof(void *)];
  std::unique_ptr<char[]> cleanupBufferHeap;
  size_t cleanupSize = scope.getCleanupSize();
  EHScopeStack::Cleanup *cleanup;
 
  // This is necessary because we are going to deallocate the cleanup
  // (in popCleanup) before we emit it.
  if (cleanupSize <= sizeof(cleanupBufferStack)) {
    memcpy(cleanupBufferStack, cleanupSource, cleanupSize);
    cleanup = reinterpret_cast<EHScopeStack::Cleanup *>(cleanupBufferStack);
  } else {
    cleanupBufferHeap.reset(new char[cleanupSize]);
    memcpy(cleanupBufferHeap.get(), cleanupSource, cleanupSize);
    cleanup =
        reinterpret_cast<EHScopeStack::Cleanup *>(cleanupBufferHeap.get());
  }
 
  EHScopeStack::Cleanup::Flags cleanupFlags;
  if (scope.isNormalCleanup())
    cleanupFlags.setIsNormalCleanupKind();
  if (scope.isEHCleanup())
    cleanupFlags.setIsEHCleanupKind();
 
  // If we have a fallthrough and no other need for the cleanup,
  // emit it directly.
  if (hasFallthrough) {
    assert(!cir::MissingFeatures::ehCleanupScopeRequiresEHCleanup());
    ehStack.popCleanup();
    scope.markEmitted();
    emitCleanup(*this, cleanupScope, cleanup, cleanupFlags);
  } else {
    // Otherwise, the best approach is to thread everything through
    // the cleanup block and then try to clean up after ourselves.
 
    // Force the entry block to exist.
    mlir::Block *normalEntry = createNormalEntry(*this, scope);
 
    // I.  Set up the fallthrough edge in.
    mlir::OpBuilder::InsertPoint savedInactiveFallthroughIP;
 
    // If we have a fallthrough source, but this cleanup is inactive,
    // save and clear the IP.
    if (!hasFallthrough && fallthroughSource) {
      assert(!isActive && "source without fallthrough for active cleanup");
      savedInactiveFallthroughIP = builder.saveInsertionPoint();
    }
 
    // II.  Emit the entry block.  This implicitly branches to it if
    // we have fallthrough.  All the fixups and existing branches
    // should already be branched to it.
    builder.setInsertionPointToEnd(normalEntry);
 
    // intercept normal cleanup to mark SEH scope end
    assert(!cir::MissingFeatures::ehCleanupScopeRequiresEHCleanup());
 
    // III.  Figure out where we're going and build the cleanup
    // epilogue.
    bool hasEnclosingCleanups =
        (scope.getEnclosingNormalCleanup() != ehStack.stable_end());
 
    // Compute the branch-through dest if we need it:
    //   - if there are branch-throughs threaded through the scope
    //   - if fall-through is a branch-through
    //   - if there are fixups that will be optimistically forwarded
    //     to the enclosing cleanup
    assert(!cir::MissingFeatures::cleanupBranchThrough());
    if (hasEnclosingCleanups)
      cgm.errorNYI("cleanup branch-through dest");
 
    mlir::Block *fallthroughDest = nullptr;
 
    // If there's exactly one branch-after and no other threads,
    // we can route it without a switch.
    // Skip for SEH, since ExitSwitch is used to generate code to indicate
    // abnormal termination. (SEH: Except _leave and fall-through at
    // the end, all other exits in a _try (return/goto/continue/break)
    // are considered as abnormal terminations, using NormalCleanupDestSlot
    // to indicate abnormal termination)
    assert(!cir::MissingFeatures::cleanupBranchThrough());
    assert(!cir::MissingFeatures::ehCleanupScopeRequiresEHCleanup());
 
    // IV.  Pop the cleanup and emit it.
    scope.markEmitted();
    ehStack.popCleanup();
    assert(ehStack.hasNormalCleanups() == hasEnclosingCleanups);
    emitCleanup(*this, cleanupScope, cleanup, cleanupFlags);
 
    // Append the prepared cleanup prologue from above.
    assert(!cir::MissingFeatures::cleanupAppendInsts());
 
    // V.  Set up the fallthrough edge out.
 
    // Case 1: a fallthrough source exists but doesn't branch to the
    // cleanup because the cleanup is inactive.
    if (!hasFallthrough && fallthroughSource) {
      // Prebranched fallthrough was forwarded earlier.
      // Non-prebranched fallthrough doesn't need to be forwarded.
      // Either way, all we need to do is restore the IP we cleared before.
      assert(!isActive);
      cgm.errorNYI("cleanup inactive fallthrough");
 
      // Case 2: a fallthrough source exists and should branch to the
      // cleanup, but we're not supposed to branch through to the next
      // cleanup.
    } else if (hasFallthrough && fallthroughDest) {
      cgm.errorNYI("cleanup fallthrough destination");
 
      // Case 3: a fallthrough source exists and should branch to the
      // cleanup and then through to the next.
    } else if (hasFallthrough) {
      // Everything is already set up for this.
 
      // Case 4: no fallthrough source exists.
    } else {
      // FIXME(cir): should we clear insertion point here?
    }
 
    // VI.  Assorted cleaning.
 
    // Check whether we can merge NormalEntry into a single predecessor.
    // This might invalidate (non-IR) pointers to NormalEntry.
    //
    // If it did invalidate those pointers, and normalEntry was the same
    // as NormalExit, go back and patch up the fixups.
    assert(!cir::MissingFeatures::simplifyCleanupEntry());
  }
}
 
/// Pops cleanup blocks until the given savepoint is reached.
void CIRGenFunction::popCleanupBlocks(
    EHScopeStack::stable_iterator oldCleanupStackDepth,
    ArrayRef<mlir::Value *> valuesToReload) {
  // If the current stack depth is the same as the cleanup stack depth,
  // we won't be exiting any cleanup scopes, so we don't need to reload
  // any values.
  bool requiresCleanup = false;
  for (auto it = ehStack.begin(), ie = ehStack.find(oldCleanupStackDepth);
       it != ie; ++it) {
    if (isa<EHCleanupScope>(&*it)) {
      requiresCleanup = true;
      break;
    }
  }
 
  // If there are values that we need to keep live, spill them now before
  // we pop the cleanup blocks. These are passed as pointers to mlir::Value
  // because we're going to replace them with the reloaded value.
  SmallVector<Address> tempAllocas;
  if (requiresCleanup) {
    for (mlir::Value *valPtr : valuesToReload) {
      mlir::Value val = *valPtr;
      if (!val)
        continue;
 
      // TODO(cir): Check for static allocas.
 
      Address temp = createDefaultAlignTempAlloca(val.getType(), val.getLoc(),
                                                  "tmp.exprcleanup");
      tempAllocas.push_back(temp);
      builder.createStore(val.getLoc(), val, temp);
    }
  }
 
  // Pop cleanup blocks until we reach the base stack depth for the
  // current scope.
  while (ehStack.stable_begin() != oldCleanupStackDepth)
    popCleanupBlock();
 
  // Reload the values that we spilled, if necessary.
  if (requiresCleanup) {
    for (auto [addr, valPtr] : llvm::zip(tempAllocas, valuesToReload)) {
      mlir::Location loc = valPtr->getLoc();
      *valPtr = builder.createLoad(loc, addr);
    }
  }
}