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-rw-r--r--lib/CodeGen/WasmEHPrepare.cpp180
1 files changed, 61 insertions, 119 deletions
diff --git a/lib/CodeGen/WasmEHPrepare.cpp b/lib/CodeGen/WasmEHPrepare.cpp
index e5002eb95346..865a1cfbf43a 100644
--- a/lib/CodeGen/WasmEHPrepare.cpp
+++ b/lib/CodeGen/WasmEHPrepare.cpp
@@ -1,14 +1,14 @@
//===-- WasmEHPrepare - Prepare excepton handling for WebAssembly --------===//
//
-// The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
+// 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 transformation is designed for use by code generators which use
-// WebAssembly exception handling scheme.
+// WebAssembly exception handling scheme. This currently supports C++
+// exceptions.
//
// WebAssembly exception handling uses Windows exception IR for the middle level
// representation. This pass does the following transformation for every
@@ -23,53 +23,20 @@
//
// - After:
// catchpad ...
-// exn = wasm.catch(0); // 0 is a tag for C++
-// wasm.landingpad.index(index);
+// exn = wasm.extract.exception();
// // Only add below in case it's not a single catch (...)
+// wasm.landingpad.index(index);
// __wasm_lpad_context.lpad_index = index;
// __wasm_lpad_context.lsda = wasm.lsda();
// _Unwind_CallPersonality(exn);
-// int selector = __wasm.landingpad_context.selector;
+// selector = __wasm.landingpad_context.selector;
// ...
//
-// Also, does the following for a cleanuppad block with a call to
-// __clang_call_terminate():
-// - Before:
-// cleanuppad ...
-// exn = wasm.get.exception();
-// __clang_call_terminate(exn);
-//
-// - After:
-// cleanuppad ...
-// exn = wasm.catch(0); // 0 is a tag for C++
-// __clang_call_terminate(exn);
-//
-//
-// * Background: WebAssembly EH instructions
-// WebAssembly's try and catch instructions are structured as follows:
-// try
-// instruction*
-// catch (C++ tag)
-// instruction*
-// ...
-// catch_all
-// instruction*
-// try_end
-//
-// A catch instruction in WebAssembly does not correspond to a C++ catch clause.
-// In WebAssembly, there is a single catch instruction for all C++ exceptions.
-// There can be more catch instructions for exceptions in other languages, but
-// they are not generated for now. catch_all catches all exceptions including
-// foreign exceptions (e.g. JavaScript). We turn catchpads into catch (C++ tag)
-// and cleanuppads into catch_all, with one exception: cleanuppad with a call to
-// __clang_call_terminate should be both in catch (C++ tag) and catch_all.
-//
//
// * Background: Direct personality function call
// In WebAssembly EH, the VM is responsible for unwinding the stack once an
// exception is thrown. After the stack is unwound, the control flow is
-// transfered to WebAssembly 'catch' instruction, which returns a caught
-// exception object.
+// transfered to WebAssembly 'catch' instruction.
//
// Unwinding the stack is not done by libunwind but the VM, so the personality
// function in libcxxabi cannot be called from libunwind during the unwinding
@@ -137,19 +104,19 @@ class WasmEHPrepare : public FunctionPass {
Value *LSDAField = nullptr; // lsda field
Value *SelectorField = nullptr; // selector
- Function *ThrowF = nullptr; // wasm.throw() intrinsic
- Function *CatchF = nullptr; // wasm.catch.extract() intrinsic
- Function *LPadIndexF = nullptr; // wasm.landingpad.index() intrinsic
- Function *LSDAF = nullptr; // wasm.lsda() intrinsic
- Function *GetExnF = nullptr; // wasm.get.exception() intrinsic
- Function *GetSelectorF = nullptr; // wasm.get.ehselector() intrinsic
- Function *CallPersonalityF = nullptr; // _Unwind_CallPersonality() wrapper
- Function *ClangCallTermF = nullptr; // __clang_call_terminate() function
+ Function *ThrowF = nullptr; // wasm.throw() intrinsic
+ Function *LPadIndexF = nullptr; // wasm.landingpad.index() intrinsic
+ Function *LSDAF = nullptr; // wasm.lsda() intrinsic
+ Function *GetExnF = nullptr; // wasm.get.exception() intrinsic
+ Function *ExtractExnF = nullptr; // wasm.extract.exception() intrinsic
+ Function *GetSelectorF = nullptr; // wasm.get.ehselector() intrinsic
+ FunctionCallee CallPersonalityF =
+ nullptr; // _Unwind_CallPersonality() wrapper
bool prepareEHPads(Function &F);
bool prepareThrows(Function &F);
- void prepareEHPad(BasicBlock *BB, unsigned Index);
+ void prepareEHPad(BasicBlock *BB, bool NeedLSDA, unsigned Index = 0);
void prepareTerminateCleanupPad(BasicBlock *BB);
public:
@@ -209,14 +176,12 @@ bool WasmEHPrepare::prepareThrows(Function &F) {
// wasm.throw() intinsic, which will be lowered to wasm 'throw' instruction.
ThrowF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_throw);
-
// Insert an unreachable instruction after a call to @llvm.wasm.throw and
// delete all following instructions within the BB, and delete all the dead
// children of the BB as well.
for (User *U : ThrowF->users()) {
- // A call to @llvm.wasm.throw() is only generated from
- // __builtin_wasm_throw() builtin call within libcxxabi, and cannot be an
- // InvokeInst.
+ // A call to @llvm.wasm.throw() is only generated from __cxa_throw()
+ // builtin call within libcxxabi, and cannot be an InvokeInst.
auto *ThrowI = cast<CallInst>(U);
if (ThrowI->getFunction() != &F)
continue;
@@ -263,8 +228,6 @@ bool WasmEHPrepare::prepareEHPads(Function &F) {
SelectorField = IRB.CreateConstGEP2_32(LPadContextTy, LPadContextGV, 0, 2,
"selector_gep");
- // wasm.catch() intinsic, which will be lowered to wasm 'catch' instruction.
- CatchF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_catch);
// wasm.landingpad.index() intrinsic, which is to specify landingpad index
LPadIndexF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_landingpad_index);
// wasm.lsda() intrinsic. Returns the address of LSDA table for the current
@@ -275,14 +238,18 @@ bool WasmEHPrepare::prepareEHPads(Function &F) {
GetExnF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_get_exception);
GetSelectorF = Intrinsic::getDeclaration(&M, Intrinsic::wasm_get_ehselector);
- // _Unwind_CallPersonality() wrapper function, which calls the personality
- CallPersonalityF = cast<Function>(M.getOrInsertFunction(
- "_Unwind_CallPersonality", IRB.getInt32Ty(), IRB.getInt8PtrTy()));
- CallPersonalityF->setDoesNotThrow();
+ // wasm.extract.exception() is the same as wasm.get.exception() but it does
+ // not take a token argument. This will be lowered down to EXTRACT_EXCEPTION
+ // pseudo instruction in instruction selection, which will be expanded using
+ // 'br_on_exn' instruction later.
+ ExtractExnF =
+ Intrinsic::getDeclaration(&M, Intrinsic::wasm_extract_exception);
- // __clang_call_terminate() function, which is inserted by clang in case a
- // cleanup throws
- ClangCallTermF = M.getFunction("__clang_call_terminate");
+ // _Unwind_CallPersonality() wrapper function, which calls the personality
+ CallPersonalityF = M.getOrInsertFunction(
+ "_Unwind_CallPersonality", IRB.getInt32Ty(), IRB.getInt8PtrTy());
+ if (Function *F = dyn_cast<Function>(CallPersonalityF.getCallee()))
+ F->setDoesNotThrow();
unsigned Index = 0;
for (auto *BB : CatchPads) {
@@ -290,60 +257,52 @@ bool WasmEHPrepare::prepareEHPads(Function &F) {
// In case of a single catch (...), we don't need to emit LSDA
if (CPI->getNumArgOperands() == 1 &&
cast<Constant>(CPI->getArgOperand(0))->isNullValue())
- prepareEHPad(BB, -1);
+ prepareEHPad(BB, false);
else
- prepareEHPad(BB, Index++);
+ prepareEHPad(BB, true, Index++);
}
- if (!ClangCallTermF)
- return !CatchPads.empty();
-
- // Cleanuppads will turn into catch_all later, but cleanuppads with a call to
- // __clang_call_terminate() is a special case. __clang_call_terminate() takes
- // an exception object, so we have to duplicate call in both 'catch <C++ tag>'
- // and 'catch_all' clauses. Here we only insert a call to catch; the
- // duplication will be done later. In catch_all, the exception object will be
- // set to null.
+ // Cleanup pads don't need LSDA.
for (auto *BB : CleanupPads)
- for (auto &I : *BB)
- if (auto *CI = dyn_cast<CallInst>(&I))
- if (CI->getCalledValue() == ClangCallTermF)
- prepareEHPad(BB, -1);
+ prepareEHPad(BB, false);
return true;
}
-void WasmEHPrepare::prepareEHPad(BasicBlock *BB, unsigned Index) {
+// Prepare an EH pad for Wasm EH handling. If NeedLSDA is false, Index is
+// ignored.
+void WasmEHPrepare::prepareEHPad(BasicBlock *BB, bool NeedLSDA,
+ unsigned Index) {
assert(BB->isEHPad() && "BB is not an EHPad!");
IRBuilder<> IRB(BB->getContext());
-
IRB.SetInsertPoint(&*BB->getFirstInsertionPt());
- // The argument to wasm.catch() is the tag for C++ exceptions, which we set to
- // 0 for this module.
- // Pseudocode: void *exn = wasm.catch(0);
- Instruction *Exn = IRB.CreateCall(CatchF, IRB.getInt32(0), "exn");
- // Replace the return value of wasm.get.exception() with the return value from
- // wasm.catch().
+
auto *FPI = cast<FuncletPadInst>(BB->getFirstNonPHI());
Instruction *GetExnCI = nullptr, *GetSelectorCI = nullptr;
for (auto &U : FPI->uses()) {
if (auto *CI = dyn_cast<CallInst>(U.getUser())) {
if (CI->getCalledValue() == GetExnF)
GetExnCI = CI;
- else if (CI->getCalledValue() == GetSelectorF)
+ if (CI->getCalledValue() == GetSelectorF)
GetSelectorCI = CI;
}
}
- assert(GetExnCI && "wasm.get.exception() call does not exist");
- GetExnCI->replaceAllUsesWith(Exn);
+ // Cleanup pads w/o __clang_call_terminate call do not have any of
+ // wasm.get.exception() or wasm.get.ehselector() calls. We need to do nothing.
+ if (!GetExnCI) {
+ assert(!GetSelectorCI &&
+ "wasm.get.ehselector() cannot exist w/o wasm.get.exception()");
+ return;
+ }
+
+ Instruction *ExtractExnCI = IRB.CreateCall(ExtractExnF, {}, "exn");
+ GetExnCI->replaceAllUsesWith(ExtractExnCI);
GetExnCI->eraseFromParent();
// In case it is a catchpad with single catch (...) or a cleanuppad, we don't
// need to call personality function because we don't need a selector.
- if (FPI->getNumArgOperands() == 0 ||
- (FPI->getNumArgOperands() == 1 &&
- cast<Constant>(FPI->getArgOperand(0))->isNullValue())) {
+ if (!NeedLSDA) {
if (GetSelectorCI) {
assert(GetSelectorCI->use_empty() &&
"wasm.get.ehselector() still has uses!");
@@ -351,7 +310,7 @@ void WasmEHPrepare::prepareEHPad(BasicBlock *BB, unsigned Index) {
}
return;
}
- IRB.SetInsertPoint(Exn->getNextNode());
+ IRB.SetInsertPoint(ExtractExnCI->getNextNode());
// This is to create a map of <landingpad EH label, landingpad index> in
// SelectionDAGISel, which is to be used in EHStreamer to emit LSDA tables.
@@ -373,12 +332,13 @@ void WasmEHPrepare::prepareEHPad(BasicBlock *BB, unsigned Index) {
IRB.CreateStore(IRB.CreateCall(LSDAF), LSDAField);
// Pseudocode: _Unwind_CallPersonality(exn);
- CallInst *PersCI =
- IRB.CreateCall(CallPersonalityF, Exn, OperandBundleDef("funclet", CPI));
+ CallInst *PersCI = IRB.CreateCall(CallPersonalityF, ExtractExnCI,
+ OperandBundleDef("funclet", CPI));
PersCI->setDoesNotThrow();
// Pseudocode: int selector = __wasm.landingpad_context.selector;
- Instruction *Selector = IRB.CreateLoad(SelectorField, "selector");
+ Instruction *Selector =
+ IRB.CreateLoad(IRB.getInt32Ty(), SelectorField, "selector");
// Replace the return value from wasm.get.ehselector() with the selector value
// loaded from __wasm_lpad_context.selector.
@@ -388,15 +348,15 @@ void WasmEHPrepare::prepareEHPad(BasicBlock *BB, unsigned Index) {
}
void llvm::calculateWasmEHInfo(const Function *F, WasmEHFuncInfo &EHInfo) {
+ // If an exception is not caught by a catchpad (i.e., it is a foreign
+ // exception), it will unwind to its parent catchswitch's unwind destination.
+ // We don't record an unwind destination for cleanuppads because every
+ // exception should be caught by it.
for (const auto &BB : *F) {
if (!BB.isEHPad())
continue;
const Instruction *Pad = BB.getFirstNonPHI();
- // If an exception is not caught by a catchpad (i.e., it is a foreign
- // exception), it will unwind to its parent catchswitch's unwind
- // destination. We don't record an unwind destination for cleanuppads
- // because every exception should be caught by it.
if (const auto *CatchPad = dyn_cast<CatchPadInst>(Pad)) {
const auto *UnwindBB = CatchPad->getCatchSwitch()->getUnwindDest();
if (!UnwindBB)
@@ -409,22 +369,4 @@ void llvm::calculateWasmEHInfo(const Function *F, WasmEHFuncInfo &EHInfo) {
EHInfo.setEHPadUnwindDest(&BB, UnwindBB);
}
}
-
- // Record the unwind destination for invoke and cleanupret instructions.
- for (const auto &BB : *F) {
- const Instruction *TI = BB.getTerminator();
- BasicBlock *UnwindBB = nullptr;
- if (const auto *Invoke = dyn_cast<InvokeInst>(TI))
- UnwindBB = Invoke->getUnwindDest();
- else if (const auto *CleanupRet = dyn_cast<CleanupReturnInst>(TI))
- UnwindBB = CleanupRet->getUnwindDest();
- if (!UnwindBB)
- continue;
- const Instruction *UnwindPad = UnwindBB->getFirstNonPHI();
- if (const auto *CatchSwitch = dyn_cast<CatchSwitchInst>(UnwindPad))
- // Currently there should be only one handler per a catchswitch.
- EHInfo.setThrowUnwindDest(&BB, *CatchSwitch->handlers().begin());
- else // cleanuppad
- EHInfo.setThrowUnwindDest(&BB, UnwindBB);
- }
}
generated by cgit v1.2.3 (git 2.25.1) at 2025-08-07 13:25:24 +0000