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[WebAssembly] Fix unwind destination mismatches in CFG stackify

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Summary:
Linearing the control flow by placing `try`/`end_try` markers can create
mismatches in unwind destinations. This patch resolves these mismatches
by wrapping those instructions with an incorrect unwind destination with
a nested `try`/`catch`/`end_try` and branching to the right destination
within the new catch block.

Reviewers: dschuff

Subscribers: sunfish, sbc100, jgravelle-google, chrib, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D48345

llvm-svn: 357343
This commit is contained in:
Heejin Ahn 2019-03-30 11:04:48 +00:00
parent e9fd9073e4
commit c4ac74fb49
3 changed files with 765 additions and 20 deletions
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530
llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
View File

@ -21,27 +21,21 @@
///
//===----------------------------------------------------------------------===//
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "WebAssembly.h"
#include "WebAssemblyExceptionInfo.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "WebAssemblySubtarget.h"
#include "WebAssemblyUtilities.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/WasmEHFuncInfo.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <cstring>
using namespace llvm;
#define DEBUG_TYPE "wasm-cfg-stackify"
STATISTIC(NumUnwindMismatches, "Number of EH pad unwind mismatches found");
namespace {
class WebAssemblyCFGStackify final : public MachineFunctionPass {
StringRef getPassName() const override { return "WebAssembly CFG Stackify"; }
@ -60,11 +54,13 @@ class WebAssemblyCFGStackify final : public MachineFunctionPass {
// over scoped regions when walking blocks.
SmallVector<MachineBasicBlock *, 8> ScopeTops;
// Placing markers.
void placeMarkers(MachineFunction &MF);
void placeBlockMarker(MachineBasicBlock &MBB);
void placeLoopMarker(MachineBasicBlock &MBB);
void placeTryMarker(MachineBasicBlock &MBB);
void removeUnnecessaryInstrs(MachineFunction &MF);
bool fixUnwindMismatches(MachineFunction &MF);
void rewriteDepthImmediates(MachineFunction &MF);
void fixEndsAtEndOfFunction(MachineFunction &MF);
@ -77,6 +73,21 @@ class WebAssemblyCFGStackify final : public MachineFunctionPass {
// <EH pad, TRY marker> map
DenseMap<const MachineBasicBlock *, MachineInstr *> EHPadToTry;
// There can be an appendix block at the end of each function, shared for:
// - creating a correct signature for fallthrough returns
// - target for rethrows that need to unwind to the caller, but are trapped
// inside another try/catch
MachineBasicBlock *AppendixBB = nullptr;
MachineBasicBlock *getAppendixBlock(MachineFunction &MF) {
if (!AppendixBB) {
AppendixBB = MF.CreateMachineBasicBlock();
// Give it a fake predecessor so that AsmPrinter prints its label.
AppendixBB->addSuccessor(AppendixBB);
MF.push_back(AppendixBB);
}
return AppendixBB;
}
// Helper functions to register / unregister scope information created by
// marker instructions.
void registerScope(MachineInstr *Begin, MachineInstr *End);
@ -94,7 +105,7 @@ public:
char WebAssemblyCFGStackify::ID = 0;
INITIALIZE_PASS(WebAssemblyCFGStackify, DEBUG_TYPE,
"Insert BLOCK and LOOP markers for WebAssembly scopes", false,
"Insert BLOCK/LOOP/TRY markers for WebAssembly scopes", false,
false)
FunctionPass *llvm::createWebAssemblyCFGStackify() {
@ -192,6 +203,8 @@ void WebAssemblyCFGStackify::unregisterScope(MachineInstr *Begin) {
}
/// Insert a BLOCK marker for branches to MBB (if needed).
// TODO Consider a more generalized way of handling block (and also loop and
// try) signatures when we implement the multi-value proposal later.
void WebAssemblyCFGStackify::placeBlockMarker(MachineBasicBlock &MBB) {
assert(!MBB.isEHPad());
MachineFunction &MF = *MBB.getParent();
@ -370,10 +383,7 @@ void WebAssemblyCFGStackify::placeLoopMarker(MachineBasicBlock &MBB) {
MachineBasicBlock *Bottom = WebAssembly::getBottom(Loop);
auto Iter = std::next(Bottom->getIterator());
if (Iter == MF.end()) {
MachineBasicBlock *Label = MF.CreateMachineBasicBlock();
// Give it a fake predecessor so that AsmPrinter prints its label.
Label->addSuccessor(Label);
MF.push_back(Label);
getAppendixBlock(MF);
Iter = std::next(Bottom->getIterator());
}
MachineBasicBlock *AfterLoop = &*Iter;
@ -454,10 +464,7 @@ void WebAssemblyCFGStackify::placeTryMarker(MachineBasicBlock &MBB) {
auto Iter = std::next(Bottom->getIterator());
if (Iter == MF.end()) {
MachineBasicBlock *Label = MF.CreateMachineBasicBlock();
// Give it a fake predecessor so that AsmPrinter prints its label.
Label->addSuccessor(Label);
MF.push_back(Label);
getAppendixBlock(MF);
Iter = std::next(Bottom->getIterator());
}
MachineBasicBlock *Cont = &*Iter;
@ -687,6 +694,488 @@ void WebAssemblyCFGStackify::removeUnnecessaryInstrs(MachineFunction &MF) {
}
}
bool WebAssemblyCFGStackify::fixUnwindMismatches(MachineFunction &MF) {
const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
MachineRegisterInfo &MRI = MF.getRegInfo();
// Linearizing the control flow by placing TRY / END_TRY markers can create
// mismatches in unwind destinations. There are two kinds of mismatches we
// try to solve here.
// 1. When an instruction may throw, but the EH pad it will unwind to can be
// different from the original CFG.
//
// Example: we have the following CFG:
// bb0:
// call @foo (if it throws, unwind to bb2)
// bb1:
// call @bar (if it throws, unwind to bb3)
// bb2 (ehpad):
// catch
// ...
// bb3 (ehpad)
// catch
// handler body
//
// And the CFG is sorted in this order. Then after placing TRY markers, it
// will look like: (BB markers are omitted)
// try $label1
// try
// call @foo
// call @bar (if it throws, unwind to bb3)
// catch <- ehpad (bb2)
// ...
// end_try
// catch <- ehpad (bb3)
// handler body
// end_try
//
// Now if bar() throws, it is going to end up ip in bb2, not bb3, where it
// is supposed to end up. We solve this problem by
// a. Split the target unwind EH pad (here bb3) so that the handler body is
// right after 'end_try', which means we extract the handler body out of
// the catch block. We do this because this handler body should be
// somewhere branch-eable from the inner scope.
// b. Wrap the call that has an incorrect unwind destination ('call @bar'
// here) with a nested try/catch/end_try scope, and within the new catch
// block, branches to the handler body.
// c. Place a branch after the newly inserted nested end_try so it can bypass
// the handler body, which is now outside of a catch block.
//
// The result will like as follows. (new: a) means this instruction is newly
// created in the process of doing 'a' above.
//
// block $label0 (new: placeBlockMarker)
// try $label1
// try
// call @foo
// try (new: b)
// call @bar
// catch (new: b)
// local.set n / drop (new: b)
// br $label1 (new: b)
// end_try (new: b)
// catch <- ehpad (bb2)
// end_try
// br $label0 (new: c)
// catch <- ehpad (bb3)
// end_try (hoisted: a)
// handler body
// end_block (new: placeBlockMarker)
//
// Note that the new wrapping block/end_block will be generated later in
// placeBlockMarker.
//
// TODO Currently local.set and local.gets are generated to move except_ref
// value created by catches. That's because we don't support yielding values
// from a block in LLVM machine IR yet, even though it is supported by wasm.
// Delete unnecessary local.get/local.sets once yielding values from a block
// is supported. The full EH spec requires multi-value support to do this, but
// for C++ we don't yet need it because we only throw a single i32.
//
// ---
// 2. The same as 1, but in this case an instruction unwinds to a caller
// function and not another EH pad.
//
// Example: we have the following CFG:
// bb0:
// call @foo (if it throws, unwind to bb2)
// bb1:
// call @bar (if it throws, unwind to caller)
// bb2 (ehpad):
// catch
// ...
//
// And the CFG is sorted in this order. Then after placing TRY markers, it
// will look like:
// try
// call @foo
// call @bar (if it throws, unwind to caller)
// catch <- ehpad (bb2)
// ...
// end_try
//
// Now if bar() throws, it is going to end up ip in bb2, when it is supposed
// throw up to the caller.
// We solve this problem by
// a. Create a new 'appendix' BB at the end of the function and put a single
// 'rethrow' instruction (+ local.get) in there.
// b. Wrap the call that has an incorrect unwind destination ('call @bar'
// here) with a nested try/catch/end_try scope, and within the new catch
// block, branches to the new appendix block.
//
// block $label0 (new: placeBlockMarker)
// try
// call @foo
// try (new: b)
// call @bar
// catch (new: b)
// local.set n (new: b)
// br $label0 (new: b)
// end_try (new: b)
// catch <- ehpad (bb2)
// ...
// end_try
// ...
// end_block (new: placeBlockMarker)
// local.get n (new: a) <- appendix block
// rethrow (new: a)
//
// In case there are multiple calls in a BB that may throw to the caller, they
// can be wrapped together in one nested try scope. (In 1, this couldn't
// happen, because may-throwing instruction there had an unwind destination,
// i.e., it was an invoke before, and there could be only one invoke within a
// BB.)
SmallVector<const MachineBasicBlock *, 8> EHPadStack;
// Range of intructions to be wrapped in a new nested try/catch
using TryRange = std::pair<MachineInstr *, MachineInstr *>;
// In original CFG, <unwind destionation BB, a vector of try ranges>
DenseMap<MachineBasicBlock *, SmallVector<TryRange, 4>> UnwindDestToTryRanges;
// In new CFG, <destination to branch to, a vector of try ranges>
DenseMap<MachineBasicBlock *, SmallVector<TryRange, 4>> BrDestToTryRanges;
// In new CFG, <destination to branch to, register containing except_ref>
DenseMap<MachineBasicBlock *, unsigned> BrDestToExnReg;
// Gather possibly throwing calls (i.e., previously invokes) whose current
// unwind destination is not the same as the original CFG.
for (auto &MBB : reverse(MF)) {
bool SeenThrowableInstInBB = false;
for (auto &MI : reverse(MBB)) {
if (MI.getOpcode() == WebAssembly::TRY)
EHPadStack.pop_back();
else if (MI.getOpcode() == WebAssembly::CATCH)
EHPadStack.push_back(MI.getParent());
// In this loop we only gather calls that have an EH pad to unwind. So
// there will be at most 1 such call (= invoke) in a BB, so after we've
// seen one, we can skip the rest of BB. Also if MBB has no EH pad
// successor or MI does not throw, this is not an invoke.
if (SeenThrowableInstInBB || !MBB.hasEHPadSuccessor() ||
!WebAssembly::mayThrow(MI))
continue;
SeenThrowableInstInBB = true;
// If the EH pad on the stack top is where this instruction should unwind
// next, we're good.
MachineBasicBlock *UnwindDest = nullptr;
for (auto *Succ : MBB.successors()) {
if (Succ->isEHPad()) {
UnwindDest = Succ;
break;
}
}
if (EHPadStack.back() == UnwindDest)
continue;
// If not, record the range.
UnwindDestToTryRanges[UnwindDest].push_back(TryRange(&MI, &MI));
}
}
assert(EHPadStack.empty());
// Gather possibly throwing calls that are supposed to unwind up to the caller
// if they throw, but currently unwind to an incorrect destination. Unlike the
// loop above, there can be multiple calls within a BB that unwind to the
// caller, which we should group together in a range.
bool NeedAppendixBlock = false;
for (auto &MBB : reverse(MF)) {
MachineInstr *RangeBegin = nullptr, *RangeEnd = nullptr; // inclusive
for (auto &MI : reverse(MBB)) {
if (MI.getOpcode() == WebAssembly::TRY)
EHPadStack.pop_back();
else if (MI.getOpcode() == WebAssembly::CATCH)
EHPadStack.push_back(MI.getParent());
// If MBB has an EH pad successor, this inst does not unwind to caller.
if (MBB.hasEHPadSuccessor())
continue;
// We wrap up the current range when we see a marker even if we haven't
// finished a BB.
if (RangeEnd && WebAssembly::isMarker(MI)) {
NeedAppendixBlock = true;
// Record the range. nullptr here means the unwind destination is the
// caller.
UnwindDestToTryRanges[nullptr].push_back(
TryRange(RangeBegin, RangeEnd));
RangeBegin = RangeEnd = nullptr; // Reset range pointers
}
// If EHPadStack is empty, that means it is correctly unwind to caller if
// it throws, so we're good. If MI does not throw, we're good too.
if (EHPadStack.empty() || !WebAssembly::mayThrow(MI))
continue;
// We found an instruction that unwinds to the caller but currently has an
// incorrect unwind destination. Create a new range or increment the
// currently existing range.
if (!RangeEnd)
RangeBegin = RangeEnd = &MI;
else
RangeBegin = &MI;
}
if (RangeEnd) {
NeedAppendixBlock = true;
// Record the range. nullptr here means the unwind destination is the
// caller.
UnwindDestToTryRanges[nullptr].push_back(TryRange(RangeBegin, RangeEnd));
RangeBegin = RangeEnd = nullptr; // Reset range pointers
}
}
assert(EHPadStack.empty());
// We don't have any unwind destination mismatches to resolve.
if (UnwindDestToTryRanges.empty())
return false;
// If we found instructions that should unwind to the caller but currently
// have incorrect unwind destination, we create an appendix block at the end
// of the function with a local.get and a rethrow instruction.
if (NeedAppendixBlock) {
auto *AppendixBB = getAppendixBlock(MF);
unsigned ExnReg =
MRI.createVirtualRegister(&WebAssembly::EXCEPT_REFRegClass);
BuildMI(AppendixBB, DebugLoc(), TII.get(WebAssembly::RETHROW))
.addReg(ExnReg);
// These instruction ranges should branch to this appendix BB.
for (auto Range : UnwindDestToTryRanges[nullptr])
BrDestToTryRanges[AppendixBB].push_back(Range);
BrDestToExnReg[AppendixBB] = ExnReg;
}
// We loop through unwind destination EH pads that are targeted from some
// inner scopes. Because these EH pads are destination of more than one scope
// now, we split them so that the handler body is after 'end_try'.
// - Before
// ehpad:
// catch
// local.set n / drop
// handler body
// ...
// cont:
// end_try
//
// - After
// ehpad:
// catch
// local.set n / drop
// brdest: (new)
// end_try (hoisted from 'cont' BB)
// handler body (taken from 'ehpad')
// ...
// cont:
for (auto &P : UnwindDestToTryRanges) {
NumUnwindMismatches++;
// This means the destination is the appendix BB, which was separately
// handled above.
if (!P.first)
continue;
MachineBasicBlock *EHPad = P.first;
// Find 'catch' and 'local.set' or 'drop' instruction that follows the
// 'catch'. If -wasm-disable-explicit-locals is not set, 'catch' should be
// always followed by either 'local.set' or a 'drop', because 'br_on_exn' is
// generated after 'catch' in LateEHPrepare and we don't support blocks
// taking values yet.
MachineInstr *Catch = nullptr;
unsigned ExnReg = 0;
for (auto &MI : *EHPad) {
switch (MI.getOpcode()) {
case WebAssembly::CATCH:
Catch = &MI;
ExnReg = Catch->getOperand(0).getReg();
break;
}
}
assert(Catch && "EH pad does not have a catch");
assert(ExnReg != 0 && "Invalid register");
auto SplitPos = std::next(Catch->getIterator());
// Create a new BB that's gonna be the destination for branches from the
// inner mismatched scope.
MachineInstr *BeginTry = EHPadToTry[EHPad];
MachineInstr *EndTry = BeginToEnd[BeginTry];
MachineBasicBlock *Cont = EndTry->getParent();
auto *BrDest = MF.CreateMachineBasicBlock();
MF.insert(std::next(EHPad->getIterator()), BrDest);
// Hoist up the existing 'end_try'.
BrDest->insert(BrDest->end(), EndTry->removeFromParent());
// Take out the handler body from EH pad to the new branch destination BB.
BrDest->splice(BrDest->end(), EHPad, SplitPos, EHPad->end());
// Fix predecessor-successor relationship.
BrDest->transferSuccessors(EHPad);
EHPad->addSuccessor(BrDest);
// All try ranges that were supposed to unwind to this EH pad now have to
// branch to this new branch dest BB.
for (auto Range : UnwindDestToTryRanges[EHPad])
BrDestToTryRanges[BrDest].push_back(Range);
BrDestToExnReg[BrDest] = ExnReg;
// In case we fall through to the continuation BB after the catch block, we
// now have to add a branch to it.
// - Before
// try
// ...
// (falls through to 'cont')
// catch
// handler body
// end
// <-- cont
//
// - After
// try
// ...
// br %cont (new)
// catch
// end
// handler body
// <-- cont
MachineBasicBlock *EHPadLayoutPred = &*std::prev(EHPad->getIterator());
MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
bool Analyzable = !TII.analyzeBranch(*EHPadLayoutPred, TBB, FBB, Cond);
if (Analyzable && !TBB && !FBB) {
DebugLoc DL = EHPadLayoutPred->empty()
? DebugLoc()
: EHPadLayoutPred->rbegin()->getDebugLoc();
BuildMI(EHPadLayoutPred, DL, TII.get(WebAssembly::BR)).addMBB(Cont);
}
}
// For possibly throwing calls whose unwind destinations are currently
// incorrect because of CFG linearization, we wrap them with a nested
// try/catch/end_try, and within the new catch block, we branch to the correct
// handler.
// - Before
// mbb:
// call @foo <- Unwind destination mismatch!
// ehpad:
// ...
//
// - After
// mbb:
// try (new)
// call @foo
// nested-ehpad: (new)
// catch (new)
// local.set n / drop (new)
// br %brdest (new)
// nested-end: (new)
// end_try (new)
// ehpad:
// ...
for (auto &P : BrDestToTryRanges) {
MachineBasicBlock *BrDest = P.first;
auto &TryRanges = P.second;
unsigned ExnReg = BrDestToExnReg[BrDest];
for (auto Range : TryRanges) {
MachineInstr *RangeBegin = nullptr, *RangeEnd = nullptr;
std::tie(RangeBegin, RangeEnd) = Range;
auto *MBB = RangeBegin->getParent();
// Include possible EH_LABELs in the range
if (RangeBegin->getIterator() != MBB->begin() &&
std::prev(RangeBegin->getIterator())->isEHLabel())
RangeBegin = &*std::prev(RangeBegin->getIterator());
if (std::next(RangeEnd->getIterator()) != MBB->end() &&
std::next(RangeEnd->getIterator())->isEHLabel())
RangeEnd = &*std::next(RangeEnd->getIterator());
MachineBasicBlock *EHPad = nullptr;
for (auto *Succ : MBB->successors()) {
if (Succ->isEHPad()) {
EHPad = Succ;
break;
}
}
// Create the nested try instruction.
MachineInstr *NestedTry =
BuildMI(*MBB, *RangeBegin, RangeBegin->getDebugLoc(),
TII.get(WebAssembly::TRY))
.addImm(int64_t(WebAssembly::ExprType::Void));
// Create the nested EH pad and fill instructions in.
MachineBasicBlock *NestedEHPad = MF.CreateMachineBasicBlock();
MF.insert(std::next(MBB->getIterator()), NestedEHPad);
NestedEHPad->setIsEHPad();
NestedEHPad->setIsEHScopeEntry();
BuildMI(NestedEHPad, RangeEnd->getDebugLoc(), TII.get(WebAssembly::CATCH),
ExnReg);
BuildMI(NestedEHPad, RangeEnd->getDebugLoc(), TII.get(WebAssembly::BR))
.addMBB(BrDest);
// Create the nested continuation BB and end_try instruction.
MachineBasicBlock *NestedCont = MF.CreateMachineBasicBlock();
MF.insert(std::next(NestedEHPad->getIterator()), NestedCont);
MachineInstr *NestedEndTry =
BuildMI(*NestedCont, NestedCont->begin(), RangeEnd->getDebugLoc(),
TII.get(WebAssembly::END_TRY));
// In case MBB has more instructions after the try range, move them to the
// new nested continuation BB.
NestedCont->splice(NestedCont->end(), MBB,
std::next(RangeEnd->getIterator()), MBB->end());
registerTryScope(NestedTry, NestedEndTry, NestedEHPad);
// Fix predecessor-successor relationship.
NestedCont->transferSuccessors(MBB);
if (EHPad)
NestedCont->removeSuccessor(EHPad);
MBB->addSuccessor(NestedEHPad);
MBB->addSuccessor(NestedCont);
NestedEHPad->addSuccessor(BrDest);
}
}
// Renumber BBs and recalculate ScopeTop info because new BBs might have been
// created and inserted above.
MF.RenumberBlocks();
ScopeTops.clear();
ScopeTops.resize(MF.getNumBlockIDs());
for (auto &MBB : reverse(MF)) {
for (auto &MI : reverse(MBB)) {
if (ScopeTops[MBB.getNumber()])
break;
switch (MI.getOpcode()) {
case WebAssembly::END_BLOCK:
case WebAssembly::END_LOOP:
case WebAssembly::END_TRY:
ScopeTops[MBB.getNumber()] = EndToBegin[&MI]->getParent();
break;
case WebAssembly::CATCH:
ScopeTops[MBB.getNumber()] = EHPadToTry[&MBB]->getParent();
break;
}
}
}
// Recompute the dominator tree.
getAnalysis<MachineDominatorTree>().runOnMachineFunction(MF);
// Place block markers for newly added branches.
SmallVector <MachineBasicBlock *, 8> BrDests;
for (auto &P : BrDestToTryRanges)
BrDests.push_back(P.first);
llvm::sort(BrDests,
[&](const MachineBasicBlock *A, const MachineBasicBlock *B) {
auto ANum = A->getNumber();
auto BNum = B->getNumber();
return ANum < BNum;
});
for (auto *Dest : BrDests)
placeBlockMarker(*Dest);
return true;
}
static unsigned
getDepth(const SmallVectorImpl<const MachineBasicBlock *> &Stack,
const MachineBasicBlock *MBB) {
@ -791,6 +1280,8 @@ void WebAssemblyCFGStackify::placeMarkers(MachineFunction &MF) {
placeBlockMarker(MBB);
}
}
// Fix mismatches in unwind destinations induced by linearizing the code.
fixUnwindMismatches(MF);
}
void WebAssemblyCFGStackify::rewriteDepthImmediates(MachineFunction &MF) {
@ -847,6 +1338,7 @@ void WebAssemblyCFGStackify::releaseMemory() {
EndToBegin.clear();
TryToEHPad.clear();
EHPadToTry.clear();
AppendixBB = nullptr;
}
bool WebAssemblyCFGStackify::runOnMachineFunction(MachineFunction &MF) {
@ -863,9 +1355,9 @@ bool WebAssemblyCFGStackify::runOnMachineFunction(MachineFunction &MF) {
// Place the BLOCK/LOOP/TRY markers to indicate the beginnings of scopes.
placeMarkers(MF);
// Remove unnecessary instructions possibly introduced by try/end_trys.
if (MCAI->getExceptionHandlingType() == ExceptionHandling::Wasm &&
MF.getFunction().hasPersonalityFn())
// Remove unnecessary instructions.
removeUnnecessaryInstrs(MF);
// Convert MBB operands in terminators to relative depth immediates.

5
llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp
View File

@ -64,6 +64,8 @@ bool WebAssembly::isCopy(const MachineInstr &MI) {
case WebAssembly::COPY_F64_S:
case WebAssembly::COPY_V128:
case WebAssembly::COPY_V128_S:
case WebAssembly::COPY_EXCEPT_REF:
case WebAssembly::COPY_EXCEPT_REF_S:
return true;
default:
return false;
@ -266,5 +268,8 @@ bool WebAssembly::mayThrow(const MachineInstr &MI) {
if (F->getName() == CxaBeginCatchFn || F->getName() == PersonalityWrapperFn ||
F->getName() == ClangCallTerminateFn || F->getName() == StdTerminateFn)
return false;
// TODO Can we exclude call instructions that are marked as 'nounwind' in the
// original LLVm IR? (Even when the callee may throw)
return true;
}

250
llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
View File

@ -1,6 +1,6 @@
; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -disable-block-placement -verify-machineinstrs -fast-isel=false -machine-sink-split-probability-threshold=0 -cgp-freq-ratio-to-skip-merge=1000 -exception-model=wasm -mattr=+exception-handling | FileCheck %s
; RUN: llc < %s -O0 -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -verify-machineinstrs -exception-model=wasm -mattr=+exception-handling | FileCheck %s --check-prefix=NOOPT
; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -disable-block-placement -verify-machineinstrs -fast-isel=false -machine-sink-split-probability-threshold=0 -cgp-freq-ratio-to-skip-merge=1000 -exception-model=wasm -mattr=+exception-handling -wasm-disable-ehpad-sort
; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -disable-block-placement -verify-machineinstrs -fast-isel=false -machine-sink-split-probability-threshold=0 -cgp-freq-ratio-to-skip-merge=1000 -exception-model=wasm -mattr=+exception-handling -wasm-disable-ehpad-sort | FileCheck %s --check-prefix=NOSORT
target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
target triple = "wasm32-unknown-unknown"
@ -368,6 +368,254 @@ try.cont: ; preds = %catch.start, %loop
br label %loop
}
; Some of test cases below are hand-tweaked by deleting some library calls to
; simplify tests and changing the order of basic blocks to cause unwind
; destination mismatches. And we use -wasm-disable-ehpad-sort to create maximum
; number of mismatches in several tests below.
; 'call bar''s original unwind destination was 'catch14', but after control flow
; linearization, its unwind destination incorrectly becomes 'catch15'. We fix
; this by wrapping the call with a nested try/catch/end_try and branching to the
; right destination (label32).
; NOSORT-LABEL: test5
; NOSORT: block
; NOSORT: try
; NOSORT: try
; NOSORT: call foo
; --- Nested try/catch/end_try starts
; NOSORT: try
; NOSORT: call bar
; NOSORT: catch $drop=
; NOSORT: br 2 # 2: down to label32
; NOSORT: end_try
; --- Nested try/catch/end_try ends
; NOSORT: br 2 # 2: down to label31
; NOSORT: catch $drop= # catch15:
; NOSORT: br 2 # 2: down to label31
; NOSORT: end_try
; NOSORT: catch $drop= # catch14:
; NOSORT: end_try # label32:
; NOSORT: end_block # label31:
; NOSORT: return
define void @test5() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
bb0:
invoke void @foo()
to label %bb1 unwind label %catch.dispatch0
bb1: ; preds = %bb0
invoke void @bar()
to label %try.cont unwind label %catch.dispatch1
catch.dispatch0: ; preds = %bb0
%0 = catchswitch within none [label %catch.start0] unwind to caller
catch.start0: ; preds = %catch.dispatch0
%1 = catchpad within %0 [i8* null]
%2 = call i8* @llvm.wasm.get.exception(token %1)
%3 = call i32 @llvm.wasm.get.ehselector(token %1)
catchret from %1 to label %try.cont
catch.dispatch1: ; preds = %bb1
%4 = catchswitch within none [label %catch.start1] unwind to caller
catch.start1: ; preds = %catch.dispatch1
%5 = catchpad within %4 [i8* null]
%6 = call i8* @llvm.wasm.get.exception(token %5)
%7 = call i32 @llvm.wasm.get.ehselector(token %5)
catchret from %5 to label %try.cont
try.cont: ; preds = %catch.start1, %catch.start0, %bb1
ret void
}
; Two 'call bar''s original unwind destination was the caller, but after control
; flow linearization, their unwind destination incorrectly becomes 'catch17'. We
; fix this by wrapping the call with a nested try/catch/end_try and branching to
; the right destination (label4), from which we rethrow the exception to the
; caller.
; NOSORT-LABEL: test6
; NOSORT: try
; NOSORT: call foo
; --- Nested try/catch/end_try starts
; NOSORT: try
; NOSORT: call bar
; NOSORT: call bar
; NOSORT: catch $[[REG:[0-9]+]]=
; NOSORT: br 1 # 1: down to label35
; NOSORT: end_try
; --- Nested try/catch/end_try ends
; NOSORT: return
; NOSORT: catch $drop= # catch17:
; NOSORT: return
; NOSORT: end_try # label35:
; NOSORT: rethrow $[[REG]] # to caller
define void @test6() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
bb0:
invoke void @foo()
to label %bb1 unwind label %catch.dispatch0
bb1: ; preds = %bb0
call void @bar()
call void @bar()
ret void
catch.dispatch0: ; preds = %bb0
%0 = catchswitch within none [label %catch.start0] unwind to caller
catch.start0: ; preds = %catch.dispatch0
%1 = catchpad within %0 [i8* null]
%2 = call i8* @llvm.wasm.get.exception(token %1)
%3 = call i32 @llvm.wasm.get.ehselector(token %1)
catchret from %1 to label %try.cont
try.cont: ; preds = %catch.start0
ret void
}
; If not for the unwind destination mismatch, the LOOP marker here would have an
; i32 signature. But because we add a rethrow instruction at the end of the
; appendix block, now the LOOP marker does not have a signature (= has a void
; signature). Here the two calls two 'bar' are supposed to throw up to the
; caller, but incorrectly unwind to 'catch19' after linearizing the CFG.
; NOSORT-LABEL: test7
; NOSORT: block
; NOSORT-NOT: loop i32
; NOSORT: loop # label38:
; NOSORT: try
; NOSORT: call foo
; --- Nested try/catch/end_try starts
; NOSORT: try
; NOSORT: call bar
; NOSORT: call bar
; NOSORT: catch $[[REG:[0-9]+]]=
; NOSORT: br 1 # 1: down to label39
; NOSORT: end_try
; --- Nested try/catch/end_try ends
; NOSORT: return {{.*}}
; NOSORT: catch $drop= # catch19:
; NOSORT: br 1 # 1: up to label38
; NOSORT: end_try # label39:
; NOSORT: end_loop
; NOSORT: end_block
; NOSORT: rethrow $[[REG]] # to caller
define i32 @test7(i32* %p) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
store volatile i32 0, i32* %p
br label %loop
loop: ; preds = %try.cont, %entry
store volatile i32 1, i32* %p
invoke void @foo()
to label %bb unwind label %catch.dispatch
bb: ; preds = %loop
call void @bar()
call void @bar()
ret i32 0
catch.dispatch: ; preds = %loop
%0 = catchswitch within none [label %catch.start] unwind to caller
catch.start: ; preds = %catch.dispatch
%1 = catchpad within %0 [i8* null]
%2 = call i8* @llvm.wasm.get.exception(token %1)
%3 = call i32 @llvm.wasm.get.ehselector(token %1)
catchret from %1 to label %try.cont
try.cont: ; preds = %catch.start
br label %loop
}
; When we have both kinds of EH pad unwind mismatches:
; - A may-throw instruction unwinds to an incorrect EH pad after linearizing the
; CFG, when it is supposed to unwind to another EH pad.
; - A may-throw instruction unwinds to an incorrect EH pad after linearizing the
; CFG, when it is supposed to unwind to the caller.
; NOSORT-LABEL: test8
; NOSORT: block
; NOSORT: block
; NOSORT: try
; NOSORT: try
; NOSORT: call foo
; --- Nested try/catch/end_try starts
; NOSORT: try
; NOSORT: call bar
; NOSORT: catch $[[REG0:[0-9]+]]=
; NOSORT: br 2 # 2: down to label43
; NOSORT: end_try
; --- Nested try/catch/end_try ends
; NOSORT: br 2 # 2: down to label42
; NOSORT: catch {{.*}}
; NOSORT: block i32
; NOSORT: br_on_exn 0, {{.*}} # 0: down to label46
; --- Nested try/catch/end_try starts
; NOSORT: try
; NOSORT: rethrow {{.*}} # down to catch24
; NOSORT: catch $[[REG1:[0-9]+]]= # catch24:
; NOSORT: br 5 # 5: down to label41
; NOSORT: end_try
; --- Nested try/catch/end_try ends
; NOSORT: end_block # label46:
; NOSORT: i32.call $drop=, __cxa_begin_catch
; --- Nested try/catch/end_try starts
; NOSORT: try
; NOSORT: call __cxa_end_catch
; NOSORT: catch $[[REG1]]=
; NOSORT: br 4 # 4: down to label41
; NOSORT: end_try
; --- Nested try/catch/end_try ends
; NOSORT: br 2 # 2: down to label42
; NOSORT: end_try
; NOSORT: catch $[[REG0]]=
; NOSORT: end_try # label43:
; NOSORT: i32.call $drop=, __cxa_begin_catch
; NOSORT: call __cxa_end_catch
; NOSORT: end_block # label42:
; NOSORT: return
; NOSORT: end_block # label41:
; NOSORT: rethrow $[[REG1]] # to caller
define void @test8() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
bb0:
invoke void @foo()
to label %bb1 unwind label %catch.dispatch0
bb1: ; preds = %bb0
invoke void @bar()
to label %try.cont unwind label %catch.dispatch1
catch.dispatch0: ; preds = %bb0
%0 = catchswitch within none [label %catch.start0] unwind to caller
catch.start0: ; preds = %catch.dispatch0
%1 = catchpad within %0 [i8* null]
%2 = call i8* @llvm.wasm.get.exception(token %1)
%3 = call i32 @llvm.wasm.get.ehselector(token %1)
%4 = call i8* @__cxa_begin_catch(i8* %2) [ "funclet"(token %1) ]
call void @__cxa_end_catch() [ "funclet"(token %1) ]
catchret from %1 to label %try.cont
catch.dispatch1: ; preds = %bb1
%5 = catchswitch within none [label %catch.start1] unwind to caller
catch.start1: ; preds = %catch.dispatch1
%6 = catchpad within %5 [i8* null]
%7 = call i8* @llvm.wasm.get.exception(token %6)
%8 = call i32 @llvm.wasm.get.ehselector(token %6)
%9 = call i8* @__cxa_begin_catch(i8* %7) [ "funclet"(token %6) ]
call void @__cxa_end_catch() [ "funclet"(token %6) ]
catchret from %6 to label %try.cont
try.cont: ; preds = %catch.start1, %catch.start0, %bb1
ret void
}
declare void @foo()
declare void @bar()
declare i32 @__gxx_wasm_personality_v0(...)