Bug Summary

File:src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/CodeGen/WasmEHPrepare.cpp
Warning:line 339, column 3
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -cc1 -triple amd64-unknown-openbsd7.0 -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name WasmEHPrepare.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -mrelocation-model pic -pic-level 1 -fhalf-no-semantic-interposition -mframe-pointer=all -relaxed-aliasing -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -fcoverage-compilation-dir=/usr/src/gnu/usr.bin/clang/libLLVM/obj -resource-dir /usr/local/lib/clang/13.0.0 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Analysis -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ASMParser -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/BinaryFormat -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Bitcode -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Bitcode -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Bitstream -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /include/llvm/CodeGen -I /include/llvm/CodeGen/PBQP -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/IR -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/IR -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Coroutines -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ProfileData/Coverage -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/CodeView -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/DWARF -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/MSF -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/PDB -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Demangle -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ExecutionEngine -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ExecutionEngine/JITLink -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ExecutionEngine/Orc -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend/OpenACC -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend/OpenMP -I /include/llvm/CodeGen/GlobalISel -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/IRReader -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/InstCombine -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/Transforms/InstCombine -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/LTO -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Linker -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/MC -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/MC/MCParser -I /include/llvm/CodeGen/MIRParser -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Object -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Option -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Passes -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ProfileData -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Scalar -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ADT -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Support -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/Symbolize -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Target -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Utils -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Vectorize -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/IPO -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include -I /usr/src/gnu/usr.bin/clang/libLLVM/../include -I /usr/src/gnu/usr.bin/clang/libLLVM/obj -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include -D NDEBUG -D __STDC_LIMIT_MACROS -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D LLVM_PREFIX="/usr" -D PIC -internal-isystem /usr/include/c++/v1 -internal-isystem /usr/local/lib/clang/13.0.0/include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/usr/src/gnu/usr.bin/clang/libLLVM/obj -ferror-limit 19 -fvisibility-inlines-hidden -fwrapv -D_RET_PROTECTOR -ret-protector -fno-rtti -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -fno-builtin-malloc -fno-builtin-calloc -fno-builtin-realloc -fno-builtin-valloc -fno-builtin-free -fno-builtin-strdup -fno-builtin-strndup -analyzer-output=html -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /home/ben/Projects/vmm/scan-build/2022-01-12-194120-40624-1 -x c++ /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/CodeGen/WasmEHPrepare.cpp
1//===-- WasmEHPrepare - Prepare excepton handling for WebAssembly --------===//
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// This transformation is designed for use by code generators which use
10// WebAssembly exception handling scheme. This currently supports C++
11// exceptions.
12//
13// WebAssembly exception handling uses Windows exception IR for the middle level
14// representation. This pass does the following transformation for every
15// catchpad block:
16// (In C-style pseudocode)
17//
18// - Before:
19// catchpad ...
20// exn = wasm.get.exception();
21// selector = wasm.get.selector();
22// ...
23//
24// - After:
25// catchpad ...
26// exn = wasm.catch(WebAssembly::CPP_EXCEPTION);
27// // Only add below in case it's not a single catch (...)
28// wasm.landingpad.index(index);
29// __wasm_lpad_context.lpad_index = index;
30// __wasm_lpad_context.lsda = wasm.lsda();
31// _Unwind_CallPersonality(exn);
32// selector = __wasm.landingpad_context.selector;
33// ...
34//
35//
36// * Background: Direct personality function call
37// In WebAssembly EH, the VM is responsible for unwinding the stack once an
38// exception is thrown. After the stack is unwound, the control flow is
39// transfered to WebAssembly 'catch' instruction.
40//
41// Unwinding the stack is not done by libunwind but the VM, so the personality
42// function in libcxxabi cannot be called from libunwind during the unwinding
43// process. So after a catch instruction, we insert a call to a wrapper function
44// in libunwind that in turn calls the real personality function.
45//
46// In Itanium EH, if the personality function decides there is no matching catch
47// clause in a call frame and no cleanup action to perform, the unwinder doesn't
48// stop there and continues unwinding. But in Wasm EH, the unwinder stops at
49// every call frame with a catch intruction, after which the personality
50// function is called from the compiler-generated user code here.
51//
52// In libunwind, we have this struct that serves as a communincation channel
53// between the compiler-generated user code and the personality function in
54// libcxxabi.
55//
56// struct _Unwind_LandingPadContext {
57// uintptr_t lpad_index;
58// uintptr_t lsda;
59// uintptr_t selector;
60// };
61// struct _Unwind_LandingPadContext __wasm_lpad_context = ...;
62//
63// And this wrapper in libunwind calls the personality function.
64//
65// _Unwind_Reason_Code _Unwind_CallPersonality(void *exception_ptr) {
66// struct _Unwind_Exception *exception_obj =
67// (struct _Unwind_Exception *)exception_ptr;
68// _Unwind_Reason_Code ret = __gxx_personality_v0(
69// 1, _UA_CLEANUP_PHASE, exception_obj->exception_class, exception_obj,
70// (struct _Unwind_Context *)__wasm_lpad_context);
71// return ret;
72// }
73//
74// We pass a landing pad index, and the address of LSDA for the current function
75// to the wrapper function _Unwind_CallPersonality in libunwind, and we retrieve
76// the selector after it returns.
77//
78//===----------------------------------------------------------------------===//
79
80#include "llvm/CodeGen/TargetLowering.h"
81#include "llvm/CodeGen/TargetSubtargetInfo.h"
82#include "llvm/CodeGen/WasmEHFuncInfo.h"
83#include "llvm/IR/IRBuilder.h"
84#include "llvm/IR/IntrinsicsWebAssembly.h"
85#include "llvm/InitializePasses.h"
86#include "llvm/Transforms/Utils/BasicBlockUtils.h"
87
88using namespace llvm;
89
90#define DEBUG_TYPE"wasmehprepare" "wasmehprepare"
91
92namespace {
93class WasmEHPrepare : public FunctionPass {
94 Type *LPadContextTy = nullptr; // type of 'struct _Unwind_LandingPadContext'
95 GlobalVariable *LPadContextGV = nullptr; // __wasm_lpad_context
96
97 // Field addresses of struct _Unwind_LandingPadContext
98 Value *LPadIndexField = nullptr; // lpad_index field
99 Value *LSDAField = nullptr; // lsda field
100 Value *SelectorField = nullptr; // selector
101
102 Function *ThrowF = nullptr; // wasm.throw() intrinsic
103 Function *LPadIndexF = nullptr; // wasm.landingpad.index() intrinsic
104 Function *LSDAF = nullptr; // wasm.lsda() intrinsic
105 Function *GetExnF = nullptr; // wasm.get.exception() intrinsic
106 Function *CatchF = nullptr; // wasm.catch() intrinsic
107 Function *GetSelectorF = nullptr; // wasm.get.ehselector() intrinsic
108 FunctionCallee CallPersonalityF =
109 nullptr; // _Unwind_CallPersonality() wrapper
110
111 bool prepareThrows(Function &F);
112 bool prepareEHPads(Function &F);
113 void prepareEHPad(BasicBlock *BB, bool NeedPersonality, unsigned Index = 0);
114
115public:
116 static char ID; // Pass identification, replacement for typeid
117
118 WasmEHPrepare() : FunctionPass(ID) {}
119 bool doInitialization(Module &M) override;
120 bool runOnFunction(Function &F) override;
121
122 StringRef getPassName() const override {
123 return "WebAssembly Exception handling preparation";
124 }
125};
126} // end anonymous namespace
127
128char WasmEHPrepare::ID = 0;
129INITIALIZE_PASS_BEGIN(WasmEHPrepare, DEBUG_TYPE,static void *initializeWasmEHPreparePassOnce(PassRegistry &
Registry) {
130 "Prepare WebAssembly exceptions", false, false)static void *initializeWasmEHPreparePassOnce(PassRegistry &
Registry) {
131INITIALIZE_PASS_END(WasmEHPrepare, DEBUG_TYPE, "Prepare WebAssembly exceptions",PassInfo *PI = new PassInfo( "Prepare WebAssembly exceptions"
, "wasmehprepare", &WasmEHPrepare::ID, PassInfo::NormalCtor_t
(callDefaultCtor<WasmEHPrepare>), false, false); Registry
.registerPass(*PI, true); return PI; } static llvm::once_flag
InitializeWasmEHPreparePassFlag; void llvm::initializeWasmEHPreparePass
(PassRegistry &Registry) { llvm::call_once(InitializeWasmEHPreparePassFlag
, initializeWasmEHPreparePassOnce, std::ref(Registry)); }
132 false, false)PassInfo *PI = new PassInfo( "Prepare WebAssembly exceptions"
, "wasmehprepare", &WasmEHPrepare::ID, PassInfo::NormalCtor_t
(callDefaultCtor<WasmEHPrepare>), false, false); Registry
.registerPass(*PI, true); return PI; } static llvm::once_flag
InitializeWasmEHPreparePassFlag; void llvm::initializeWasmEHPreparePass
(PassRegistry &Registry) { llvm::call_once(InitializeWasmEHPreparePassFlag
, initializeWasmEHPreparePassOnce, std::ref(Registry)); }
133
134FunctionPass *llvm::createWasmEHPass() { return new WasmEHPrepare(); }
135
136bool WasmEHPrepare::doInitialization(Module &M) {
137 IRBuilder<> IRB(M.getContext());
138 LPadContextTy = StructType::get(IRB.getInt32Ty(), // lpad_index
139 IRB.getInt8PtrTy(), // lsda
140 IRB.getInt32Ty() // selector
141 );
142 return false;
143}
144
145// Erase the specified BBs if the BB does not have any remaining predecessors,
146// and also all its dead children.
147template <typename Container>
148static void eraseDeadBBsAndChildren(const Container &BBs) {
149 SmallVector<BasicBlock *, 8> WL(BBs.begin(), BBs.end());
150 while (!WL.empty()) {
151 auto *BB = WL.pop_back_val();
152 if (!pred_empty(BB))
153 continue;
154 WL.append(succ_begin(BB), succ_end(BB));
155 DeleteDeadBlock(BB);
156 }
157}
158
159bool WasmEHPrepare::runOnFunction(Function &F) {
160 bool Changed = false;
161 Changed |= prepareThrows(F);
162 Changed |= prepareEHPads(F);
1
Calling 'WasmEHPrepare::prepareEHPads'
163 return Changed;
164}
165
166bool WasmEHPrepare::prepareThrows(Function &F) {
167 Module &M = *F.getParent();
168 IRBuilder<> IRB(F.getContext());
169 bool Changed = false;
170
171 // wasm.throw() intinsic, which will be lowered to wasm 'throw' instruction.
172 ThrowF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_throw);
173 // Insert an unreachable instruction after a call to @llvm.wasm.throw and
174 // delete all following instructions within the BB, and delete all the dead
175 // children of the BB as well.
176 for (User *U : ThrowF->users()) {
177 // A call to @llvm.wasm.throw() is only generated from __cxa_throw()
178 // builtin call within libcxxabi, and cannot be an InvokeInst.
179 auto *ThrowI = cast<CallInst>(U);
180 if (ThrowI->getFunction() != &F)
181 continue;
182 Changed = true;
183 auto *BB = ThrowI->getParent();
184 SmallVector<BasicBlock *, 4> Succs(successors(BB));
185 auto &InstList = BB->getInstList();
186 InstList.erase(std::next(BasicBlock::iterator(ThrowI)), InstList.end());
187 IRB.SetInsertPoint(BB);
188 IRB.CreateUnreachable();
189 eraseDeadBBsAndChildren(Succs);
190 }
191
192 return Changed;
193}
194
195bool WasmEHPrepare::prepareEHPads(Function &F) {
196 Module &M = *F.getParent();
197 IRBuilder<> IRB(F.getContext());
198
199 SmallVector<BasicBlock *, 16> CatchPads;
200 SmallVector<BasicBlock *, 16> CleanupPads;
201 for (BasicBlock &BB : F) {
202 if (!BB.isEHPad())
203 continue;
204 auto *Pad = BB.getFirstNonPHI();
205 if (isa<CatchPadInst>(Pad))
206 CatchPads.push_back(&BB);
207 else if (isa<CleanupPadInst>(Pad))
208 CleanupPads.push_back(&BB);
209 }
210 if (CatchPads.empty() && CleanupPads.empty())
211 return false;
212
213 assert(F.hasPersonalityFn() && "Personality function not found")((void)0);
214
215 // __wasm_lpad_context global variable
216 LPadContextGV = cast<GlobalVariable>(
2
The object is a 'GlobalVariable'
217 M.getOrInsertGlobal("__wasm_lpad_context", LPadContextTy));
218 LPadIndexField = IRB.CreateConstGEP2_32(LPadContextTy, LPadContextGV, 0, 0,
219 "lpad_index_gep");
220 LSDAField =
221 IRB.CreateConstGEP2_32(LPadContextTy, LPadContextGV, 0, 1, "lsda_gep");
222 SelectorField = IRB.CreateConstGEP2_32(LPadContextTy, LPadContextGV, 0, 2,
223 "selector_gep");
224
225 // wasm.landingpad.index() intrinsic, which is to specify landingpad index
226 LPadIndexF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_landingpad_index);
227 // wasm.lsda() intrinsic. Returns the address of LSDA table for the current
228 // function.
229 LSDAF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_lsda);
230 // wasm.get.exception() and wasm.get.ehselector() intrinsics. Calls to these
231 // are generated in clang.
232 GetExnF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_get_exception);
233 GetSelectorF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_get_ehselector);
234
235 // wasm.catch() will be lowered down to wasm 'catch' instruction in
236 // instruction selection.
237 CatchF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_catch);
238
239 // _Unwind_CallPersonality() wrapper function, which calls the personality
240 CallPersonalityF = M.getOrInsertFunction(
241 "_Unwind_CallPersonality", IRB.getInt32Ty(), IRB.getInt8PtrTy());
242 if (Function *F
3.1
'F' is null
= dyn_cast<Function>(CallPersonalityF.getCallee()))
3
Assuming the object is not a 'Function'
4
Taking false branch
243 F->setDoesNotThrow();
244
245 unsigned Index = 0;
246 for (auto *BB : CatchPads) {
5
Assuming '__begin1' is not equal to '__end1'
247 auto *CPI = cast<CatchPadInst>(BB->getFirstNonPHI());
6
The object is a 'CatchPadInst'
248 // In case of a single catch (...), we don't need to emit a personalify
249 // function call
250 if (CPI->getNumArgOperands() == 1 &&
7
Assuming the condition is false
251 cast<Constant>(CPI->getArgOperand(0))->isNullValue())
252 prepareEHPad(BB, false);
253 else
254 prepareEHPad(BB, true, Index++);
8
Calling 'WasmEHPrepare::prepareEHPad'
255 }
256
257 // Cleanup pads don't need a personality function call.
258 for (auto *BB : CleanupPads)
259 prepareEHPad(BB, false);
260
261 return true;
262}
263
264// Prepare an EH pad for Wasm EH handling. If NeedPersonality is false, Index is
265// ignored.
266void WasmEHPrepare::prepareEHPad(BasicBlock *BB, bool NeedPersonality,
267 unsigned Index) {
268 assert(BB->isEHPad() && "BB is not an EHPad!")((void)0);
269 IRBuilder<> IRB(BB->getContext());
270 IRB.SetInsertPoint(&*BB->getFirstInsertionPt());
271
272 auto *FPI = cast<FuncletPadInst>(BB->getFirstNonPHI());
9
The object is a 'FuncletPadInst'
273 Instruction *GetExnCI = nullptr, *GetSelectorCI = nullptr;
10
'GetSelectorCI' initialized to a null pointer value
274 for (auto &U : FPI->uses()) {
275 if (auto *CI
11.1
'CI' is non-null
= dyn_cast<CallInst>(U.getUser())) {
11
Assuming the object is a 'CallInst'
12
Taking true branch
276 if (CI->getCalledOperand() == GetExnF)
13
Assuming the condition is true
14
Taking true branch
277 GetExnCI = CI;
278 if (CI->getCalledOperand() == GetSelectorF)
15
Assuming the condition is false
16
Taking false branch
279 GetSelectorCI = CI;
280 }
281 }
282
283 // Cleanup pads do not have any of wasm.get.exception() or
284 // wasm.get.ehselector() calls. We need to do nothing.
285 if (!GetExnCI
16.1
'GetExnCI' is non-null
) {
17
Taking false branch
286 assert(!GetSelectorCI &&((void)0)
287 "wasm.get.ehselector() cannot exist w/o wasm.get.exception()")((void)0);
288 return;
289 }
290
291 // Replace wasm.get.exception intrinsic with wasm.catch intrinsic, which will
292 // be lowered to wasm 'catch' instruction. We do this mainly because
293 // instruction selection cannot handle wasm.get.exception intrinsic's token
294 // argument.
295 Instruction *CatchCI =
296 IRB.CreateCall(CatchF, {IRB.getInt32(WebAssembly::CPP_EXCEPTION)}, "exn");
297 GetExnCI->replaceAllUsesWith(CatchCI);
298 GetExnCI->eraseFromParent();
299
300 // In case it is a catchpad with single catch (...) or a cleanuppad, we don't
301 // need to call personality function because we don't need a selector.
302 if (!NeedPersonality
17.1
'NeedPersonality' is true
) {
18
Taking false branch
303 if (GetSelectorCI) {
304 assert(GetSelectorCI->use_empty() &&((void)0)
305 "wasm.get.ehselector() still has uses!")((void)0);
306 GetSelectorCI->eraseFromParent();
307 }
308 return;
309 }
310 IRB.SetInsertPoint(CatchCI->getNextNode());
311
312 // This is to create a map of <landingpad EH label, landingpad index> in
313 // SelectionDAGISel, which is to be used in EHStreamer to emit LSDA tables.
314 // Pseudocode: wasm.landingpad.index(Index);
315 IRB.CreateCall(LPadIndexF, {FPI, IRB.getInt32(Index)});
316
317 // Pseudocode: __wasm_lpad_context.lpad_index = index;
318 IRB.CreateStore(IRB.getInt32(Index), LPadIndexField);
319
320 auto *CPI = cast<CatchPadInst>(FPI);
19
'FPI' is a 'CatchPadInst'
321 // TODO Sometimes storing the LSDA address every time is not necessary, in
322 // case it is already set in a dominating EH pad and there is no function call
323 // between from that EH pad to here. Consider optimizing those cases.
324 // Pseudocode: __wasm_lpad_context.lsda = wasm.lsda();
325 IRB.CreateStore(IRB.CreateCall(LSDAF), LSDAField);
326
327 // Pseudocode: _Unwind_CallPersonality(exn);
328 CallInst *PersCI = IRB.CreateCall(CallPersonalityF, CatchCI,
329 OperandBundleDef("funclet", CPI));
330 PersCI->setDoesNotThrow();
331
332 // Pseudocode: int selector = __wasm.landingpad_context.selector;
333 Instruction *Selector =
334 IRB.CreateLoad(IRB.getInt32Ty(), SelectorField, "selector");
335
336 // Replace the return value from wasm.get.ehselector() with the selector value
337 // loaded from __wasm_lpad_context.selector.
338 assert(GetSelectorCI && "wasm.get.ehselector() call does not exist")((void)0);
339 GetSelectorCI->replaceAllUsesWith(Selector);
20
Called C++ object pointer is null
340 GetSelectorCI->eraseFromParent();
341}
342
343void llvm::calculateWasmEHInfo(const Function *F, WasmEHFuncInfo &EHInfo) {
344 // If an exception is not caught by a catchpad (i.e., it is a foreign
345 // exception), it will unwind to its parent catchswitch's unwind destination.
346 // We don't record an unwind destination for cleanuppads because every
347 // exception should be caught by it.
348 for (const auto &BB : *F) {
349 if (!BB.isEHPad())
350 continue;
351 const Instruction *Pad = BB.getFirstNonPHI();
352
353 if (const auto *CatchPad = dyn_cast<CatchPadInst>(Pad)) {
354 const auto *UnwindBB = CatchPad->getCatchSwitch()->getUnwindDest();
355 if (!UnwindBB)
356 continue;
357 const Instruction *UnwindPad = UnwindBB->getFirstNonPHI();
358 if (const auto *CatchSwitch = dyn_cast<CatchSwitchInst>(UnwindPad))
359 // Currently there should be only one handler per a catchswitch.
360 EHInfo.setUnwindDest(&BB, *CatchSwitch->handlers().begin());
361 else // cleanuppad
362 EHInfo.setUnwindDest(&BB, UnwindBB);
363 }
364 }
365}