LLVM: lib/Target/WebAssembly/WebAssemblyExceptionInfo.cpp Source File

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WebAssemblyExceptionInfo.cpp
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1//===--- WebAssemblyExceptionInfo.cpp - Exception Infomation --------------===//
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/// \file
10/// \brief This file implements WebAssemblyException information analysis.
11///
12//===----------------------------------------------------------------------===//
13
14#include "WebAssemblyExceptionInfo.h"
15#include "WebAssemblyUtilities.h"
16#include "llvm/ADT/DepthFirstIterator.h"
17#include "llvm/ADT/PostOrderIterator.h"
18#include "llvm/CodeGen/MachineDominanceFrontier.h"
19#include "llvm/CodeGen/MachineDominators.h"
20#include "llvm/CodeGen/WasmEHFuncInfo.h"
21#include "llvm/IR/Function.h"
22#include "llvm/InitializePasses.h"
23#include "llvm/MC/MCAsmInfo.h"
24#include "llvm/Target/TargetMachine.h"
25
26using namespace llvm;
27
28 #define DEBUG_TYPE "wasm-exception-info"
29
30char WebAssemblyExceptionInfo::ID = 0;
31
32 INITIALIZE_PASS_BEGIN(WebAssemblyExceptionInfo, DEBUG_TYPE,
33 "WebAssembly Exception Information", true, true)
34INITIALIZE_PASS_DEPENDENCY(MachineDominatorTreeWrapperPass)
35INITIALIZE_PASS_DEPENDENCY(MachineDominanceFrontier)
36 INITIALIZE_PASS_END(WebAssemblyExceptionInfo, DEBUG_TYPE,
37 "WebAssembly Exception Information", true, true)
38
40 LLVM_DEBUG(dbgs() << "********** Exception Info Calculation **********\n"
41 "********** Function: "
42 << MF.getName() << '\n');
44 if (MF.getTarget().getMCAsmInfo()->getExceptionHandlingType() !=
46 !MF.getFunction().hasPersonalityFn())
47 return false;
48 auto &MDT = getAnalysis<MachineDominatorTreeWrapperPass>().getDomTree();
50 recalculate(MF, MDT, MDF);
52 return false;
53}
54
55// Check if Dst is reachable from Src using BFS. Search only within BBs
56// dominated by Header.
58 const MachineBasicBlock *Dst,
59 const MachineBasicBlock *Header,
60 const MachineDominatorTree &MDT) {
61 assert(MDT.dominates(Header, Dst));
64 WL.push_back(Src);
65
66 while (!WL.empty()) {
67 const auto *MBB = WL.pop_back_val();
68 if (MBB == Dst)
69 return true;
70 Visited.insert(MBB);
71 for (auto *Succ : MBB->successors())
72 if (!Visited.count(Succ) && MDT.dominates(Header, Succ))
73 WL.push_back(Succ);
74 }
75 return false;
76}
77
80 const MachineDominanceFrontier &MDF) {
81 // Postorder traversal of the dominator tree.
83 for (auto *DomNode : post_order(&MDT)) {
84 MachineBasicBlock *EHPad = DomNode->getBlock();
85 if (!EHPad->isEHPad())
86 continue;
87 auto WE = std::make_unique<WebAssemblyException>(EHPad);
88 discoverAndMapException(WE.get(), MDT, MDF);
89 Exceptions.push_back(std::move(WE));
90 }
91
92 // WasmEHFuncInfo contains a map of <catchpad, its next unwind destination>,
93 // which means, if an exception is not caught by the catchpad, it should end
94 // up in the next unwind destination stored in this data structure. (It is
95 // written as catchswitch's 'unwind' destination in ll files.) The below is an
96 // intuitive example of their relationship in C++ code:
97 // try {
98 // try {
99 // } catch (int) { // catchpad
100 // ... // this catch (int) { ... } is grouped as an exception
101 // }
102 // } catch (...) { // next unwind destination
103 // }
104 // (The example is try-catches for illustration purpose, but the unwind
105 // destination can be also a cleanuppad generated by destructor calls.) So the
106 // unwind destination is in the outside of the catchpad's exception.
107 //
108 // We group exceptions in this analysis simply by including all BBs dominated
109 // by an EH pad. But in case the EH pad's unwind destination does not have any
110 // children outside of the exception, that unwind destination ends up also
111 // being dominated by the EH pad and included in the exception, which is not
112 // semantically correct, because it unwinds/rethrows into an inner scope.
113 //
114 // Here we extract those unwind destinations from their (incorrect) parent
115 // exception. Note that the unwind destinations may not be an immediate
116 // children of the parent exception, so we have to traverse the parent chain.
117 //
118 // We should traverse BBs in the preorder of the dominator tree, because
119 // otherwise the result can be incorrect. For example, when there are three
120 // exceptions A, B, and C and A > B > C (> is subexception relationship here),
121 // and A's unwind destination is B and B's is C. When we visit B before A, we
122 // end up extracting C only out of B but not out of A.
123 const auto *EHInfo = MF.getWasmEHFuncInfo();
124 assert(EHInfo);
126 UnwindWEVec;
127 for (auto *DomNode : depth_first(&MDT)) {
128 MachineBasicBlock *EHPad = DomNode->getBlock();
129 if (!EHPad->isEHPad())
130 continue;
131 if (!EHInfo->hasUnwindDest(EHPad))
132 continue;
133 auto *UnwindDest = EHInfo->getUnwindDest(EHPad);
134 auto *SrcWE = getExceptionFor(EHPad);
135 auto *DstWE = getExceptionFor(UnwindDest);
136 if (SrcWE->contains(DstWE)) {
137 UnwindWEVec.push_back(std::make_pair(SrcWE, DstWE));
138 LLVM_DEBUG(dbgs() << "Unwind destination ExceptionInfo fix:\n "
139 << DstWE->getEHPad()->getNumber() << "."
140 << DstWE->getEHPad()->getName()
141 << "'s exception is taken out of "
142 << SrcWE->getEHPad()->getNumber() << "."
143 << SrcWE->getEHPad()->getName() << "'s exception\n");
144 DstWE->setParentException(SrcWE->getParentException());
145 }
146 }
147
148 // After fixing subexception relationship between unwind destinations above,
149 // there can still be remaining discrepancies.
150 //
151 // For example, suppose Exception A is dominated by EHPad A and Exception B is
152 // dominated by EHPad B. EHPad A's unwind destination is EHPad B, but because
153 // EHPad B is dominated by EHPad A, the initial grouping makes Exception B a
154 // subexception of Exception A, and we fix it by taking Exception B out of
155 // Exception A above. But there can still be remaining BBs within Exception A
156 // that are reachable from Exception B. These BBs semantically don't belong
157 // to Exception A and were not a part of this 'catch' clause or cleanup code
158 // in the original code, but they just happened to be grouped within Exception
159 // A because they were dominated by EHPad A. We fix this case by taking those
160 // BBs out of the incorrect exception and all its subexceptions that it
161 // belongs to.
162 //
163 // 1. First, we take out remaining incorrect subexceptions. This part is
164 // easier, because we haven't added BBs to exceptions yet, we only need to
165 // change parent exception pointer.
166 for (auto *DomNode : depth_first(&MDT)) {
167 MachineBasicBlock *EHPad = DomNode->getBlock();
168 if (!EHPad->isEHPad())
169 continue;
170 auto *WE = getExceptionFor(EHPad);
171
172 // For each source EHPad -> unwind destination EHPad
173 for (auto &P : UnwindWEVec) {
174 auto *SrcWE = P.first;
175 auto *DstWE = P.second;
176 // If WE (the current EH pad's exception) is still contained in SrcWE but
177 // reachable from DstWE that was taken out of SrcWE above, we have to take
178 // out WE out of SrcWE too.
179 if (WE != SrcWE && SrcWE->contains(WE) && !DstWE->contains(WE) &&
180 isReachableAmongDominated(DstWE->getEHPad(), EHPad, SrcWE->getEHPad(),
181 MDT)) {
182 LLVM_DEBUG(dbgs() << "Remaining reachable ExceptionInfo fix:\n "
183 << WE->getEHPad()->getNumber() << "."
184 << WE->getEHPad()->getName()
185 << "'s exception is taken out of "
186 << SrcWE->getEHPad()->getNumber() << "."
187 << SrcWE->getEHPad()->getName() << "'s exception\n");
188 WE->setParentException(SrcWE->getParentException());
189 }
190 }
191 }
192
193 // Add BBs to exceptions' block set. This is a preparation to take out
194 // remaining incorect BBs from exceptions, because we need to iterate over BBs
195 // for each exception.
196 for (auto *DomNode : post_order(&MDT)) {
197 MachineBasicBlock *MBB = DomNode->getBlock();
199 for (; WE; WE = WE->getParentException())
200 WE->addToBlocksSet(MBB);
201 }
202
203 // 2. We take out remaining individual BBs out. Now we have added BBs to each
204 // exceptions' BlockSet, when we take a BB out of an exception, we need to fix
205 // those sets too.
206 for (auto &P : UnwindWEVec) {
207 auto *SrcWE = P.first;
208 auto *DstWE = P.second;
209
210 SrcWE->getBlocksSet().remove_if([&](MachineBasicBlock *MBB){
211 if (MBB->isEHPad()) {
212 assert(!isReachableAmongDominated(DstWE->getEHPad(), MBB,
213 SrcWE->getEHPad(), MDT) &&
214 "We already handled EH pads above");
215 return false;
216 }
217 if (isReachableAmongDominated(DstWE->getEHPad(), MBB, SrcWE->getEHPad(),
218 MDT)) {
219 LLVM_DEBUG(dbgs() << "Remainder BB: " << MBB->getNumber() << "."
220 << MBB->getName() << " is\n");
222 while (InnerWE != SrcWE) {
224 << " removed from " << InnerWE->getEHPad()->getNumber()
225 << "." << InnerWE->getEHPad()->getName()
226 << "'s exception\n");
227 InnerWE->removeFromBlocksSet(MBB);
228 InnerWE = InnerWE->getParentException();
229 }
230 LLVM_DEBUG(dbgs() << " removed from " << SrcWE->getEHPad()->getNumber()
231 << "." << SrcWE->getEHPad()->getName()
232 << "'s exception\n");
233 changeExceptionFor(MBB, SrcWE->getParentException());
234 if (SrcWE->getParentException())
235 SrcWE->getParentException()->addToBlocksSet(MBB);
236 return true;
237 }
238 return false;
239 });
240 }
241
242 // Add BBs to exceptions' block vector
243 for (auto *DomNode : post_order(&MDT)) {
244 MachineBasicBlock *MBB = DomNode->getBlock();
246 for (; WE; WE = WE->getParentException())
248 }
249
251 ExceptionPointers.reserve(Exceptions.size());
252
253 // Add subexceptions to exceptions
254 for (auto &WE : Exceptions) {
255 ExceptionPointers.push_back(WE.get());
256 if (WE->getParentException())
257 WE->getParentException()->getSubExceptions().push_back(std::move(WE));
258 else
259 addTopLevelException(std::move(WE));
260 }
261
262 // For convenience, Blocks and SubExceptions are inserted in postorder.
263 // Reverse the lists.
264 for (auto *WE : ExceptionPointers) {
265 WE->reverseBlock();
266 std::reverse(WE->getSubExceptions().begin(), WE->getSubExceptions().end());
267 }
268}
269
271 BBMap.clear();
272 TopLevelExceptions.clear();
273}
274
281
282void WebAssemblyExceptionInfo::discoverAndMapException(
283 WebAssemblyException *WE, const MachineDominatorTree &MDT,
284 const MachineDominanceFrontier &MDF) {
285 unsigned NumBlocks = 0;
286 unsigned NumSubExceptions = 0;
287
288 // Map blocks that belong to a catchpad / cleanuppad
289 MachineBasicBlock *EHPad = WE->getEHPad();
290 SmallVector<MachineBasicBlock *, 8> WL;
291 WL.push_back(EHPad);
292 while (!WL.empty()) {
293 MachineBasicBlock *MBB = WL.pop_back_val();
294
295 // Find its outermost discovered exception. If this is a discovered block,
296 // check if it is already discovered to be a subexception of this exception.
297 WebAssemblyException *SubE = getOutermostException(MBB);
298 if (SubE) {
299 if (SubE != WE) {
300 // Discover a subexception of this exception.
301 SubE->setParentException(WE);
302 ++NumSubExceptions;
303 NumBlocks += SubE->getBlocksVector().capacity();
304 // All blocks that belong to this subexception have been already
305 // discovered. Skip all of them. Add the subexception's landing pad's
306 // dominance frontier to the worklist.
307 for (auto &Frontier : MDF.find(SubE->getEHPad())->second)
308 if (MDT.dominates(EHPad, Frontier))
309 WL.push_back(Frontier);
310 }
311 continue;
312 }
313
314 // This is an undiscovered block. Map it to the current exception.
315 changeExceptionFor(MBB, WE);
316 ++NumBlocks;
317
318 // Add successors dominated by the current BB to the worklist.
319 for (auto *Succ : MBB->successors())
320 if (MDT.dominates(EHPad, Succ))
321 WL.push_back(Succ);
322 }
323
324 WE->getSubExceptions().reserve(NumSubExceptions);
325 WE->reserveBlocks(NumBlocks);
326}
327
328WebAssemblyException *
329WebAssemblyExceptionInfo::getOutermostException(MachineBasicBlock *MBB) const {
330 WebAssemblyException *WE = getExceptionFor(MBB);
331 if (WE) {
332 while (WebAssemblyException *Parent = WE->getParentException())
333 WE = Parent;
334 }
335 return WE;
336}
337
339 OS.indent(Depth * 2) << "Exception at depth " << getExceptionDepth()
340 << " containing: ";
341
342 for (unsigned I = 0; I < getBlocks().size(); ++I) {
344 if (I)
345 OS << ", ";
346 OS << "%bb." << MBB->getNumber();
347 if (const auto *BB = MBB->getBasicBlock())
348 if (BB->hasName())
349 OS << "." << BB->getName();
350
351 if (getEHPad() == MBB)
352 OS << " (landing-pad)";
353 }
354 OS << "\n";
355
356 for (auto &SubE : SubExceptions)
357 SubE->print(OS, Depth + 2);
358}
359
360#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
361 LLVM_DUMP_METHOD void WebAssemblyException::dump() const { print(dbgs()); }
362#endif
363
365 WE.print(OS);
366 return OS;
367}
368
370 for (auto &WE : TopLevelExceptions)
371 WE->print(OS);
372}
assert(UImm &&(UImm !=~static_cast< T >(0)) &&"Invalid immediate!")
MachineBasicBlock & MBB
#define LLVM_DUMP_METHOD
Mark debug helper function definitions like dump() that should not be stripped from debug builds.
Definition Compiler.h:638
This file builds on the ADT/GraphTraits.h file to build generic depth first graph iterator.
#define DEBUG_TYPE
I
#define I(x, y, z)
Definition MD5.cpp:58
P
#define P(N)
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition PassSupport.h:42
#define INITIALIZE_PASS_END(passName, arg, name, cfg, analysis)
Definition PassSupport.h:44
#define INITIALIZE_PASS_BEGIN(passName, arg, name, cfg, analysis)
Definition PassSupport.h:39
This file builds on the ADT/GraphTraits.h file to build a generic graph post order iterator.
#define LLVM_DEBUG(...)
Definition Debug.h:114
static bool isReachableAmongDominated(const MachineBasicBlock *Src, const MachineBasicBlock *Dst, const MachineBasicBlock *Header, const MachineDominatorTree &MDT)
This file implements WebAssemblyException information analysis.
This file contains the declaration of the WebAssembly-specific utility functions.
Represent the analysis usage information of a pass.
AnalysisUsage & addRequired()
void setPreservesAll()
Set by analyses that do not transform their input at all.
bool isEHPad() const
Returns true if the block is a landing pad.
int getNumber() const
MachineBasicBlocks are uniquely numbered at the function level, unless they're not in a MachineFuncti...
iterator_range< succ_iterator > successors()
LLVM_ABI StringRef getName() const
Return the name of the corresponding LLVM basic block, or an empty string.
iterator find(MachineBasicBlock *B)
Analysis pass which computes a MachineDominatorTree.
DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to compute a normal dominat...
bool dominates(const MachineInstr *A, const MachineInstr *B) const
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
const WasmEHFuncInfo * getWasmEHFuncInfo() const
getWasmEHFuncInfo - Return information about how the current function uses Wasm exception handling.
A Module instance is used to store all the information related to an LLVM module.
Definition Module.h:67
AnalysisType & getAnalysis() const
getAnalysis<AnalysisType>() - This function is used by subclasses to get to the analysis information ...
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition SmallPtrSet.h:455
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition SmallPtrSet.h:389
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition SmallPtrSet.h:527
void reserve(size_type N)
Definition SmallVector.h:664
void push_back(const T &Elt)
Definition SmallVector.h:417
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition SmallVector.h:1203
void changeExceptionFor(const MachineBasicBlock *MBB, WebAssemblyException *WE)
bool runOnMachineFunction(MachineFunction &) override
runOnMachineFunction - This method must be overloaded to perform the desired machine code transformat...
void addTopLevelException(std::unique_ptr< WebAssemblyException > WE)
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
void recalculate(MachineFunction &MF, MachineDominatorTree &MDT, const MachineDominanceFrontier &MDF)
WebAssemblyException * getExceptionFor(const MachineBasicBlock *MBB) const
void print(raw_ostream &OS, const Module *M=nullptr) const override
print - Print out the internal state of the pass.
void releaseMemory() override
releaseMemory() - This member can be implemented by a pass if it wants to be able to release its memo...
void print(raw_ostream &OS, unsigned Depth=0) const
MachineBasicBlock * getEHPad() const
void addToBlocksSet(MachineBasicBlock *MBB)
const std::vector< std::unique_ptr< WebAssemblyException > > & getSubExceptions() const
ArrayRef< MachineBasicBlock * > getBlocks() const
std::vector< MachineBasicBlock * > & getBlocksVector()
WebAssemblyException * getParentException() const
void removeFromBlocksSet(MachineBasicBlock *MBB)
void setParentException(WebAssemblyException *WE)
void addToBlocksVector(MachineBasicBlock *MBB)
This class implements an extremely fast bulk output stream that can only output to a stream.
Definition raw_ostream.h:53
raw_ostream & indent(unsigned NumSpaces)
indent - Insert 'NumSpaces' spaces.
This is an optimization pass for GlobalISel generic memory operations.
Definition AddressRanges.h:18
void dump(const SparseBitVector< ElementSize > &LHS, raw_ostream &out)
@ Wasm
WebAssembly Exception Handling.
Definition CodeGen.h:59
iterator_range< po_iterator< T > > post_order(const T &G)
LLVM_ABI raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition Debug.cpp:207
raw_ostream & operator<<(raw_ostream &OS, const APFixedPoint &FX)
Definition APFixedPoint.h:312
iterator_range< df_iterator< T > > depth_first(const T &G)
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