EHScopeStack.h source code [clang_source_code/lib/CodeGen/EHScopeStack.h]

1	//===-- EHScopeStack.h - Stack for cleanup IR generation --------- C++ --===//
2	//
3	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4	// See https://llvm.org/LICENSE.txt for license information.
5	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6	//
7	//===----------------------------------------------------------------------===//
8	//
9	// These classes should be the minimum interface required for other parts of
10	// CodeGen to emit cleanups. The implementation is in CGCleanup.cpp and other
11	// implemenentation details that are not widely needed are in CGCleanup.h.
12	//
13	//===----------------------------------------------------------------------===//
14
15	#ifndef LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H
16	#define LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H
17
18	#include "clang/Basic/LLVM.h"
19	#include "llvm/ADT/STLExtras.h"
20	#include "llvm/ADT/SmallVector.h"
21	#include "llvm/IR/BasicBlock.h"
22	#include "llvm/IR/Instructions.h"
23	#include "llvm/IR/Value.h"
24
25	namespace clang {
26	namespace CodeGen {
27
28	class CodeGenFunction;
29
30	/// A branch fixup. These are required when emitting a goto to a
31	/// label which hasn't been emitted yet. The goto is optimistically
32	/// emitted as a branch to the basic block for the label, and (if it
33	/// occurs in a scope with non-trivial cleanups) a fixup is added to
34	/// the innermost cleanup. When a (normal) cleanup is popped, any
35	/// unresolved fixups in that scope are threaded through the cleanup.
36	struct BranchFixup {
37	/// The block containing the terminator which needs to be modified
38	/// into a switch if this fixup is resolved into the current scope.
39	/// If null, LatestBranch points directly to the destination.
40	llvm::BasicBlock *OptimisticBranchBlock;
41
42	/// The ultimate destination of the branch.
43	///
44	/// This can be set to null to indicate that this fixup was
45	/// successfully resolved.
46	llvm::BasicBlock *Destination;
47
48	/// The destination index value.
49	unsigned DestinationIndex;
50
51	/// The initial branch of the fixup.
52	llvm::BranchInst *InitialBranch;
53	};
54
55	template <class T> struct InvariantValue {
56	typedef T type;
57	typedef T saved_type;
58	static bool needsSaving(type value) { return false; }
59	static saved_type save(CodeGenFunction &CGF, type value) { return value; }
60	static type restore(CodeGenFunction &CGF, saved_type value) { return value; }
61	};
62
63	/// A metaprogramming class for ensuring that a value will dominate an
64	/// arbitrary position in a function.
65	template <class T> struct DominatingValue : InvariantValue<T> {};
66
67	template <class T, bool mightBeInstruction =
68	std::is_base_of<llvm::Value, T>::value &&
69	!std::is_base_of<llvm::Constant, T>::value &&
70	!std::is_base_of<llvm::BasicBlock, T>::value>
71	struct DominatingPointer;
72	template <class T> struct DominatingPointer<T,false> : InvariantValue<T*> {};
73	// template <class T> struct DominatingPointer<T,true> at end of file
74
75	template <class T> struct DominatingValue<T*> : DominatingPointer<T> {};
76
77	enum CleanupKind : unsigned {
78	/// Denotes a cleanup that should run when a scope is exited using exceptional
79	/// control flow (a throw statement leading to stack unwinding, ).
80	EHCleanup = 0x1,
81
82	/// Denotes a cleanup that should run when a scope is exited using normal
83	/// control flow (falling off the end of the scope, return, goto, ...).
84	NormalCleanup = 0x2,
85
86	NormalAndEHCleanup = EHCleanup \| NormalCleanup,
87
88	InactiveCleanup = 0x4,
89	InactiveEHCleanup = EHCleanup \| InactiveCleanup,
90	InactiveNormalCleanup = NormalCleanup \| InactiveCleanup,
91	InactiveNormalAndEHCleanup = NormalAndEHCleanup \| InactiveCleanup,
92
93	LifetimeMarker = 0x8,
94	NormalEHLifetimeMarker = LifetimeMarker \| NormalAndEHCleanup,
95	};
96
97	/// A stack of scopes which respond to exceptions, including cleanups
98	/// and catch blocks.
99	class EHScopeStack {
100	public:
101	/* Should switch to alignof(uint64_t) instead of 8, when EHCleanupScope can */
102	enum { ScopeStackAlignment = 8 };
103
104	/// A saved depth on the scope stack. This is necessary because
105	/// pushing scopes onto the stack invalidates iterators.
106	class stable_iterator {
107	friend class EHScopeStack;
108
109	/// Offset from StartOfData to EndOfBuffer.
110	ptrdiff_t Size;
111
112	stable_iterator(ptrdiff_t Size) : Size(Size) {}
113
114	public:
115	static stable_iterator invalid() { return stable_iterator(-1); }
116	stable_iterator() : Size(-1) {}
117
118	bool isValid() const { return Size >= 0; }
119
120	/// Returns true if this scope encloses I.
121	/// Returns false if I is invalid.
122	/// This scope must be valid.
123	bool encloses(stable_iterator I) const { return Size <= I.Size; }
124
125	/// Returns true if this scope strictly encloses I: that is,
126	/// if it encloses I and is not I.
127	/// Returns false is I is invalid.
128	/// This scope must be valid.
129	bool strictlyEncloses(stable_iterator I) const { return Size < I.Size; }
130
131	friend bool operator==(stable_iterator A, stable_iterator B) {
132	return A.Size == B.Size;
133	}
134	friend bool operator!=(stable_iterator A, stable_iterator B) {
135	return A.Size != B.Size;
136	}
137	};
138
139	/// Information for lazily generating a cleanup. Subclasses must be
140	/// POD-like: cleanups will not be destructed, and they will be
141	/// allocated on the cleanup stack and freely copied and moved
142	/// around.
143	///
144	/// Cleanup implementations should generally be declared in an
145	/// anonymous namespace.
146	class Cleanup {
147	// Anchor the construction vtable.
148	virtual void anchor();
149
150	protected:
151	~Cleanup() = default;
152
153	public:
154	Cleanup(const Cleanup &) = default;
155	Cleanup(Cleanup &&) {}
156	Cleanup() = default;
157
158	/// Generation flags.
159	class Flags {
160	enum {
161	F_IsForEH = 0x1,
162	F_IsNormalCleanupKind = 0x2,
163	F_IsEHCleanupKind = 0x4
164	};
165	unsigned flags;
166
167	public:
168	Flags() : flags(0) {}
169
170	/// isForEH - true if the current emission is for an EH cleanup.
171	bool isForEHCleanup() const { return flags & F_IsForEH; }
172	bool isForNormalCleanup() const { return !isForEHCleanup(); }
173	void setIsForEHCleanup() { flags \|= F_IsForEH; }
174
175	bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; }
176	void setIsNormalCleanupKind() { flags \|= F_IsNormalCleanupKind; }
177
178	/// isEHCleanupKind - true if the cleanup was pushed as an EH
179	/// cleanup.
180	bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
181	void setIsEHCleanupKind() { flags \|= F_IsEHCleanupKind; }
182	};
183
184
185	/// Emit the cleanup. For normal cleanups, this is run in the
186	/// same EH context as when the cleanup was pushed, i.e. the
187	/// immediately-enclosing context of the cleanup scope. For
188	/// EH cleanups, this is run in a terminate context.
189	///
190	// \param flags cleanup kind.
191	virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0;
192	};
193
194	/// ConditionalCleanup stores the saved form of its parameters,
195	/// then restores them and performs the cleanup.
196	template <class T, class... As>
197	class ConditionalCleanup final : public Cleanup {
198	typedef std::tuple<typename DominatingValue<As>::saved_type...> SavedTuple;
199	SavedTuple Saved;
200
201	template <std::size_t... Is>
202	T restore(CodeGenFunction &CGF, llvm::index_sequence<Is...>) {
203	// It's important that the restores are emitted in order. The braced init
204	// list guarantees that.
205	return T{DominatingValue<As>::restore(CGF, std::get<Is>(Saved))...};
206	}
207
208	void Emit(CodeGenFunction &CGF, Flags flags) override {
209	restore(CGF, llvm::index_sequence_for<As...>()).Emit(CGF, flags);
210	}
211
212	public:
213	ConditionalCleanup(typename DominatingValue<As>::saved_type... A)
214	: Saved(A...) {}
215
216	ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {}
217	};
218
219	private:
220	// The implementation for this class is in CGException.h and
221	// CGException.cpp; the definition is here because it's used as a
222	// member of CodeGenFunction.
223
224	/// The start of the scope-stack buffer, i.e. the allocated pointer
225	/// for the buffer. All of these pointers are either simultaneously
226	/// null or simultaneously valid.
227	char *StartOfBuffer;
228
229	/// The end of the buffer.
230	char *EndOfBuffer;
231
232	/// The first valid entry in the buffer.
233	char *StartOfData;
234
235	/// The innermost normal cleanup on the stack.
236	stable_iterator InnermostNormalCleanup;
237
238	/// The innermost EH scope on the stack.
239	stable_iterator InnermostEHScope;
240
241	/// The current set of branch fixups. A branch fixup is a jump to
242	/// an as-yet unemitted label, i.e. a label for which we don't yet
243	/// know the EH stack depth. Whenever we pop a cleanup, we have
244	/// to thread all the current branch fixups through it.
245	///
246	/// Fixups are recorded as the Use of the respective branch or
247	/// switch statement. The use points to the final destination.
248	/// When popping out of a cleanup, these uses are threaded through
249	/// the cleanup and adjusted to point to the new cleanup.
250	///
251	/// Note that branches are allowed to jump into protected scopes
252	/// in certain situations; e.g. the following code is legal:
253	/// struct A { ~A(); }; // trivial ctor, non-trivial dtor
254	/// goto foo;
255	/// A a;
256	/// foo:
257	/// bar();
258	SmallVector<BranchFixup, 8> BranchFixups;
259
260	char *allocate(size_t Size);
261	void deallocate(size_t Size);
262
263	void *pushCleanup(CleanupKind K, size_t DataSize);
264
265	public:
266	EHScopeStack() : StartOfBuffer(nullptr), EndOfBuffer(nullptr),
267	StartOfData(nullptr), InnermostNormalCleanup(stable_end()),
268	InnermostEHScope(stable_end()) {}
269	~EHScopeStack() { delete[] StartOfBuffer; }
270
271	/// Push a lazily-created cleanup on the stack.
272	template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) {
273	static_assert(alignof(T) <= ScopeStackAlignment,
274	"Cleanup's alignment is too large.");
275	void *Buffer = pushCleanup(Kind, sizeof(T));
276	Cleanup *Obj = new (Buffer) T(A...);
277	(void) Obj;
278	}
279
280	/// Push a lazily-created cleanup on the stack. Tuple version.
281	template <class T, class... As>
282	void pushCleanupTuple(CleanupKind Kind, std::tuple<As...> A) {
283	static_assert(alignof(T) <= ScopeStackAlignment,
284	"Cleanup's alignment is too large.");
285	void *Buffer = pushCleanup(Kind, sizeof(T));
286	Cleanup *Obj = new (Buffer) T(std::move(A));
287	(void) Obj;
288	}
289
290	// Feel free to add more variants of the following:
291
292	/// Push a cleanup with non-constant storage requirements on the
293	/// stack. The cleanup type must provide an additional static method:
294	/// static size_t getExtraSize(size_t);
295	/// The argument to this method will be the value N, which will also
296	/// be passed as the first argument to the constructor.
297	///
298	/// The data stored in the extra storage must obey the same
299	/// restrictions as normal cleanup member data.
300	///
301	/// The pointer returned from this method is valid until the cleanup
302	/// stack is modified.
303	template <class T, class... As>
304	T *pushCleanupWithExtra(CleanupKind Kind, size_t N, As... A) {
305	static_assert(alignof(T) <= ScopeStackAlignment,
306	"Cleanup's alignment is too large.");
307	void *Buffer = pushCleanup(Kind, sizeof(T) + T::getExtraSize(N));
308	return new (Buffer) T(N, A...);
309	}
310
311	void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
312	void *Buffer = pushCleanup(Kind, Size);
313	std::memcpy(Buffer, Cleanup, Size);
314	}
315
316	/// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
317	void popCleanup();
318
319	/// Push a set of catch handlers on the stack. The catch is
320	/// uninitialized and will need to have the given number of handlers
321	/// set on it.
322	class EHCatchScope *pushCatch(unsigned NumHandlers);
323
324	/// Pops a catch scope off the stack. This is private to CGException.cpp.
325	void popCatch();
326
327	/// Push an exceptions filter on the stack.
328	class EHFilterScope *pushFilter(unsigned NumFilters);
329
330	/// Pops an exceptions filter off the stack.
331	void popFilter();
332
333	/// Push a terminate handler on the stack.
334	void pushTerminate();
335
336	/// Pops a terminate handler off the stack.
337	void popTerminate();
338
339	// Returns true iff the current scope is either empty or contains only
340	// lifetime markers, i.e. no real cleanup code
341	bool containsOnlyLifetimeMarkers(stable_iterator Old) const;
342
343	/// Determines whether the exception-scopes stack is empty.
344	bool empty() const { return StartOfData == EndOfBuffer; }
345
346	bool requiresLandingPad() const;
347
348	/// Determines whether there are any normal cleanups on the stack.
349	bool hasNormalCleanups() const {
350	return InnermostNormalCleanup != stable_end();
351	}
352
353	/// Returns the innermost normal cleanup on the stack, or
354	/// stable_end() if there are no normal cleanups.
355	stable_iterator getInnermostNormalCleanup() const {
356	return InnermostNormalCleanup;
357	}
358	stable_iterator getInnermostActiveNormalCleanup() const;
359
360	stable_iterator getInnermostEHScope() const {
361	return InnermostEHScope;
362	}
363
364
365	/// An unstable reference to a scope-stack depth. Invalidated by
366	/// pushes but not pops.
367	class iterator;
368
369	/// Returns an iterator pointing to the innermost EH scope.
370	iterator begin() const;
371
372	/// Returns an iterator pointing to the outermost EH scope.
373	iterator end() const;
374
375	/// Create a stable reference to the top of the EH stack. The
376	/// returned reference is valid until that scope is popped off the
377	/// stack.
378	stable_iterator stable_begin() const {
379	return stable_iterator(EndOfBuffer - StartOfData);
380	}
381
382	/// Create a stable reference to the bottom of the EH stack.
383	static stable_iterator stable_end() {
384	return stable_iterator(0);
385	}
386
387	/// Translates an iterator into a stable_iterator.
388	stable_iterator stabilize(iterator it) const;
389
390	/// Turn a stable reference to a scope depth into a unstable pointer
391	/// to the EH stack.
392	iterator find(stable_iterator save) const;
393
394	/// Add a branch fixup to the current cleanup scope.
395	BranchFixup &addBranchFixup() {
396	(0) . __assert_fail ("hasNormalCleanups() && \"adding fixup in scope without cleanups\"", "/home/seafit/code_projects/clang_source/clang/lib/CodeGen/EHScopeStack.h", 396, __PRETTY_FUNCTION__))" file_link="../../../include/assert.h.html#88" macro="true">assert(hasNormalCleanups() && "adding fixup in scope without cleanups");
397	BranchFixups.push_back(BranchFixup());
398	return BranchFixups.back();
399	}
400
401	unsigned getNumBranchFixups() const { return BranchFixups.size(); }
402	BranchFixup &getBranchFixup(unsigned I) {
403	assert(I < getNumBranchFixups());
404	return BranchFixups[I];
405	}
406
407	/// Pops lazily-removed fixups from the end of the list. This
408	/// should only be called by procedures which have just popped a
409	/// cleanup or resolved one or more fixups.
410	void popNullFixups();
411
412	/// Clears the branch-fixups list. This should only be called by
413	/// ResolveAllBranchFixups.
414	void clearFixups() { BranchFixups.clear(); }
415	};
416
417	} // namespace CodeGen
418	} // namespace clang
419
420	#endif
421