static void EmitCleanup(CodeGenFunction &CGF,
EHScopeStack::Cleanup *Fn,
EHScopeStack::Cleanup::Flags flags,
llvm::Value *ActiveFlag) {
// EH cleanups always occur within a terminate scope.
if (flags.isForEHCleanup()) CGF.EHStack.pushTerminate();
// If there's an active flag, load it and skip the cleanup if it's
// false.
llvm::BasicBlock *ContBB = nullptr;
if (ActiveFlag) {
ContBB = CGF.createBasicBlock("cleanup.done");
llvm::BasicBlock *CleanupBB = CGF.createBasicBlock("cleanup.action");
llvm::Value *IsActive
= CGF.Builder.CreateLoad(ActiveFlag, "cleanup.is_active");
CGF.Builder.CreateCondBr(IsActive, CleanupBB, ContBB);
CGF.EmitBlock(CleanupBB);
}
// Ask the cleanup to emit itself.
Fn->Emit(CGF, flags);
assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
// Emit the continuation block if there was an active flag.
if (ActiveFlag)
CGF.EmitBlock(ContBB);
// Leave the terminate scope.
if (flags.isForEHCleanup()) CGF.EHStack.popTerminate();
}
static void EmitCleanup(CodeGenFunction &CGF,
EHScopeStack::Cleanup *Fn,
EHScopeStack::Cleanup::Flags flags,
llvm::Value *ActiveFlag) {
// Itanium EH cleanups occur within a terminate scope. Microsoft SEH doesn't
// have this behavior, and the Microsoft C++ runtime will call terminate for
// us if the cleanup throws.
bool PushedTerminate = false;
if (flags.isForEHCleanup() && !CGF.getTarget().getCXXABI().isMicrosoft()) {
CGF.EHStack.pushTerminate();
PushedTerminate = true;
}
// If there's an active flag, load it and skip the cleanup if it's
// false.
llvm::BasicBlock *ContBB = nullptr;
if (ActiveFlag) {
ContBB = CGF.createBasicBlock("cleanup.done");
llvm::BasicBlock *CleanupBB = CGF.createBasicBlock("cleanup.action");
llvm::Value *IsActive
= CGF.Builder.CreateLoad(ActiveFlag, "cleanup.is_active");
CGF.Builder.CreateCondBr(IsActive, CleanupBB, ContBB);
CGF.EmitBlock(CleanupBB);
}
// Ask the cleanup to emit itself.
Fn->Emit(CGF, flags);
assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
// Emit the continuation block if there was an active flag.
if (ActiveFlag)
CGF.EmitBlock(ContBB);
// Leave the terminate scope.
if (PushedTerminate)
CGF.EHStack.popTerminate();
}
/// Pops a cleanup block. If the block includes a normal cleanup, the
/// current insertion point is threaded through the cleanup, as are
/// any branch fixups on the cleanup.
void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
assert(!EHStack.empty() && "cleanup stack is empty!");
assert(isa<EHCleanupScope>(*EHStack.begin()) && "top not a cleanup!");
EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
assert(Scope.getFixupDepth() <= EHStack.getNumBranchFixups());
// Remember activation information.
bool IsActive = Scope.isActive();
llvm::Value *NormalActiveFlag =
Scope.shouldTestFlagInNormalCleanup() ? Scope.getActiveFlag() : nullptr;
llvm::Value *EHActiveFlag =
Scope.shouldTestFlagInEHCleanup() ? Scope.getActiveFlag() : nullptr;
// Check whether we need an EH cleanup. This is only true if we've
// generated a lazy EH cleanup block.
llvm::BasicBlock *EHEntry = Scope.getCachedEHDispatchBlock();
assert(Scope.hasEHBranches() == (EHEntry != nullptr));
bool RequiresEHCleanup = (EHEntry != nullptr);
EHScopeStack::stable_iterator EHParent = Scope.getEnclosingEHScope();
// Check the three conditions which might require a normal cleanup:
// - whether there are branch fix-ups through this cleanup
unsigned FixupDepth = Scope.getFixupDepth();
bool HasFixups = EHStack.getNumBranchFixups() != FixupDepth;
// - whether there are branch-throughs or branch-afters
bool HasExistingBranches = Scope.hasBranches();
// - whether there's a fallthrough
llvm::BasicBlock *FallthroughSource = Builder.GetInsertBlock();
bool HasFallthrough = (FallthroughSource != nullptr && IsActive);
// Branch-through fall-throughs leave the insertion point set to the
// end of the last cleanup, which points to the current scope. The
// rest of IR gen doesn't need to worry about this; it only happens
// during the execution of PopCleanupBlocks().
bool HasPrebranchedFallthrough =
(FallthroughSource && FallthroughSource->getTerminator());
// If this is a normal cleanup, then having a prebranched
// fallthrough implies that the fallthrough source unconditionally
// jumps here.
assert(!Scope.isNormalCleanup() || !HasPrebranchedFallthrough ||
(Scope.getNormalBlock() &&
FallthroughSource->getTerminator()->getSuccessor(0)
== Scope.getNormalBlock()));
bool RequiresNormalCleanup = false;
if (Scope.isNormalCleanup() &&
(HasFixups || HasExistingBranches || HasFallthrough)) {
RequiresNormalCleanup = true;
}
// If we have a prebranched fallthrough into an inactive normal
// cleanup, rewrite it so that it leads to the appropriate place.
if (Scope.isNormalCleanup() && HasPrebranchedFallthrough && !IsActive) {
llvm::BasicBlock *prebranchDest;
// If the prebranch is semantically branching through the next
// cleanup, just forward it to the next block, leaving the
// insertion point in the prebranched block.
if (FallthroughIsBranchThrough) {
EHScope &enclosing = *EHStack.find(Scope.getEnclosingNormalCleanup());
prebranchDest = CreateNormalEntry(*this, cast<EHCleanupScope>(enclosing));
// Otherwise, we need to make a new block. If the normal cleanup
// isn't being used at all, we could actually reuse the normal
// entry block, but this is simpler, and it avoids conflicts with
// dead optimistic fixup branches.
} else {
prebranchDest = createBasicBlock("forwarded-prebranch");
EmitBlock(prebranchDest);
}
llvm::BasicBlock *normalEntry = Scope.getNormalBlock();
assert(normalEntry && !normalEntry->use_empty());
ForwardPrebranchedFallthrough(FallthroughSource,
normalEntry, prebranchDest);
}
// If we don't need the cleanup at all, we're done.
if (!RequiresNormalCleanup && !RequiresEHCleanup) {
destroyOptimisticNormalEntry(*this, Scope);
EHStack.popCleanup(); // safe because there are no fixups
assert(EHStack.getNumBranchFixups() == 0 ||
EHStack.hasNormalCleanups());
return;
}
// Copy the cleanup emission data out. Note that SmallVector
// guarantees maximal alignment for its buffer regardless of its
// type parameter.
SmallVector<char, 8*sizeof(void*)> CleanupBuffer;
CleanupBuffer.reserve(Scope.getCleanupSize());
memcpy(CleanupBuffer.data(),
Scope.getCleanupBuffer(), Scope.getCleanupSize());
CleanupBuffer.set_size(Scope.getCleanupSize());
EHScopeStack::Cleanup *Fn =
reinterpret_cast<EHScopeStack::Cleanup*>(CleanupBuffer.data());
EHScopeStack::Cleanup::Flags cleanupFlags;
if (Scope.isNormalCleanup())
cleanupFlags.setIsNormalCleanupKind();
if (Scope.isEHCleanup())
cleanupFlags.setIsEHCleanupKind();
if (!RequiresNormalCleanup) {
destroyOptimisticNormalEntry(*this, Scope);
EHStack.popCleanup();
} else {
// If we have a fallthrough and no other need for the cleanup,
// emit it directly.
if (HasFallthrough && !HasPrebranchedFallthrough &&
!HasFixups && !HasExistingBranches) {
destroyOptimisticNormalEntry(*this, Scope);
EHStack.popCleanup();
EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
// Otherwise, the best approach is to thread everything through
// the cleanup block and then try to clean up after ourselves.
} else {
// Force the entry block to exist.
llvm::BasicBlock *NormalEntry = CreateNormalEntry(*this, Scope);
// I. Set up the fallthrough edge in.
CGBuilderTy::InsertPoint savedInactiveFallthroughIP;
// If there's a fallthrough, we need to store the cleanup
// destination index. For fall-throughs this is always zero.
if (HasFallthrough) {
if (!HasPrebranchedFallthrough)
Builder.CreateStore(Builder.getInt32(0), getNormalCleanupDestSlot());
// Otherwise, save and clear the IP if we don't have fallthrough
// because the cleanup is inactive.
} else if (FallthroughSource) {
assert(!IsActive && "source without fallthrough for active cleanup");
savedInactiveFallthroughIP = Builder.saveAndClearIP();
}
// 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.
EmitBlock(NormalEntry);
// 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
llvm::BasicBlock *BranchThroughDest = nullptr;
if (Scope.hasBranchThroughs() ||
(FallthroughSource && FallthroughIsBranchThrough) ||
(HasFixups && HasEnclosingCleanups)) {
assert(HasEnclosingCleanups);
EHScope &S = *EHStack.find(Scope.getEnclosingNormalCleanup());
BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S));
}
llvm::BasicBlock *FallthroughDest = nullptr;
SmallVector<llvm::Instruction*, 2> InstsToAppend;
// If there's exactly one branch-after and no other threads,
// we can route it without a switch.
if (!Scope.hasBranchThroughs() && !HasFixups && !HasFallthrough &&
Scope.getNumBranchAfters() == 1) {
assert(!BranchThroughDest || !IsActive);
// TODO: clean up the possibly dead stores to the cleanup dest slot.
llvm::BasicBlock *BranchAfter = Scope.getBranchAfterBlock(0);
InstsToAppend.push_back(llvm::BranchInst::Create(BranchAfter));
// Build a switch-out if we need it:
// - if there are branch-afters threaded through the scope
// - if fall-through is a branch-after
// - if there are fixups that have nowhere left to go and
// so must be immediately resolved
} else if (Scope.getNumBranchAfters() ||
(HasFallthrough && !FallthroughIsBranchThrough) ||
(HasFixups && !HasEnclosingCleanups)) {
llvm::BasicBlock *Default =
(BranchThroughDest ? BranchThroughDest : getUnreachableBlock());
// TODO: base this on the number of branch-afters and fixups
const unsigned SwitchCapacity = 10;
llvm::LoadInst *Load =
new llvm::LoadInst(getNormalCleanupDestSlot(), "cleanup.dest");
llvm::SwitchInst *Switch =
llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
InstsToAppend.push_back(Load);
InstsToAppend.push_back(Switch);
// Branch-after fallthrough.
if (FallthroughSource && !FallthroughIsBranchThrough) {
FallthroughDest = createBasicBlock("cleanup.cont");
if (HasFallthrough)
Switch->addCase(Builder.getInt32(0), FallthroughDest);
}
for (unsigned I = 0, E = Scope.getNumBranchAfters(); I != E; ++I) {
Switch->addCase(Scope.getBranchAfterIndex(I),
Scope.getBranchAfterBlock(I));
}
// If there aren't any enclosing cleanups, we can resolve all
// the fixups now.
if (HasFixups && !HasEnclosingCleanups)
ResolveAllBranchFixups(*this, Switch, NormalEntry);
} else {
// We should always have a branch-through destination in this case.
assert(BranchThroughDest);
InstsToAppend.push_back(llvm::BranchInst::Create(BranchThroughDest));
}
// IV. Pop the cleanup and emit it.
EHStack.popCleanup();
assert(EHStack.hasNormalCleanups() == HasEnclosingCleanups);
EmitCleanup(*this, Fn, cleanupFlags, NormalActiveFlag);
// Append the prepared cleanup prologue from above.
llvm::BasicBlock *NormalExit = Builder.GetInsertBlock();
for (unsigned I = 0, E = InstsToAppend.size(); I != E; ++I)
NormalExit->getInstList().push_back(InstsToAppend[I]);
// Optimistically hope that any fixups will continue falling through.
for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
I < E; ++I) {
BranchFixup &Fixup = EHStack.getBranchFixup(I);
if (!Fixup.Destination) continue;
if (!Fixup.OptimisticBranchBlock) {
new llvm::StoreInst(Builder.getInt32(Fixup.DestinationIndex),
getNormalCleanupDestSlot(),
Fixup.InitialBranch);
Fixup.InitialBranch->setSuccessor(0, NormalEntry);
}
Fixup.OptimisticBranchBlock = NormalExit;
}
// 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);
Builder.restoreIP(savedInactiveFallthroughIP);
// 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) {
assert(!FallthroughIsBranchThrough);
EmitBlock(FallthroughDest);
// 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 {
Builder.ClearInsertionPoint();
}
// VI. Assorted cleaning.
// Check whether we can merge NormalEntry into a single predecessor.
// This might invalidate (non-IR) pointers to NormalEntry.
llvm::BasicBlock *NewNormalEntry =
SimplifyCleanupEntry(*this, NormalEntry);
// If it did invalidate those pointers, and NormalEntry was the same
// as NormalExit, go back and patch up the fixups.
if (NewNormalEntry != NormalEntry && NormalEntry == NormalExit)
for (unsigned I = FixupDepth, E = EHStack.getNumBranchFixups();
I < E; ++I)
EHStack.getBranchFixup(I).OptimisticBranchBlock = NewNormalEntry;
}
}
assert(EHStack.hasNormalCleanups() || EHStack.getNumBranchFixups() == 0);
// Emit the EH cleanup if required.
if (RequiresEHCleanup) {
ApplyDebugLocation AutoRestoreLocation(*this, CurEHLocation);
CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
EmitBlock(EHEntry);
// We only actually emit the cleanup code if the cleanup is either
// active or was used before it was deactivated.
if (EHActiveFlag || IsActive) {
cleanupFlags.setIsForEHCleanup();
EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag);
}
Builder.CreateBr(getEHDispatchBlock(EHParent));
Builder.restoreIP(SavedIP);
SimplifyCleanupEntry(*this, EHEntry);
}
}