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[WebAssembly] Fix delegate's argument computation
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I previously assumed `delegate`'s immediate argument computation
followed a different rule than that of branches, but we agreed to make
it the same
(WebAssembly/exception-handling#146). This
removes the need for a separate `DelegateStack` in both CFGStackify and
InstPrinter.

When computing the immediate argument, we use a different function for
`delegate` computation because in MIR `DELEGATE`'s instruction's
destination is the destination catch BB or delegate BB, and when it is a
catch BB, we need an additional step of getting its corresponding `end`
marker.

Reviewed By: tlively, dschuff

Differential Revision: https://reviews.llvm.org/D96525
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@aheejin
aheejin committed Feb 12, 2021
1 parent e434fc0 commit 2968611
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Showing 4 changed files with 80 additions and 64 deletions.
32 changes: 14 additions & 18 deletions llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyInstPrinter.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -93,42 +93,37 @@ void WebAssemblyInstPrinter::printInst(const MCInst *MI, uint64_t Address,
case WebAssembly::LOOP:
case WebAssembly::LOOP_S:
printAnnotation(OS, "label" + utostr(ControlFlowCounter) + ':');
ControlFlowStack.push_back(std::make_pair(ControlFlowCounter, true));
DelegateStack.push_back(ControlFlowCounter++);
ControlFlowStack.push_back(std::make_pair(ControlFlowCounter++, true));
return;

case WebAssembly::BLOCK:
case WebAssembly::BLOCK_S:
ControlFlowStack.push_back(std::make_pair(ControlFlowCounter, false));
DelegateStack.push_back(ControlFlowCounter++);
ControlFlowStack.push_back(std::make_pair(ControlFlowCounter++, false));
return;

case WebAssembly::TRY:
case WebAssembly::TRY_S:
ControlFlowStack.push_back(std::make_pair(ControlFlowCounter, false));
EHPadStack.push_back(ControlFlowCounter);
DelegateStack.push_back(ControlFlowCounter++);
EHPadStack.push_back(ControlFlowCounter++);
EHInstStack.push_back(TRY);
return;

case WebAssembly::END_LOOP:
case WebAssembly::END_LOOP_S:
if (ControlFlowStack.empty() || DelegateStack.empty()) {
if (ControlFlowStack.empty()) {
printAnnotation(OS, "End marker mismatch!");
} else {
ControlFlowStack.pop_back();
DelegateStack.pop_back();
}
return;

case WebAssembly::END_BLOCK:
case WebAssembly::END_BLOCK_S:
if (ControlFlowStack.empty() || DelegateStack.empty()) {
if (ControlFlowStack.empty()) {
printAnnotation(OS, "End marker mismatch!");
} else {
printAnnotation(
OS, "label" + utostr(ControlFlowStack.pop_back_val().first) + ':');
DelegateStack.pop_back();
}
return;

Expand All @@ -154,12 +149,11 @@ void WebAssemblyInstPrinter::printInst(const MCInst *MI, uint64_t Address,
} else if (EHInstStack.back() == CATCH_ALL) {
printAnnotation(OS, "catch/catch_all cannot occur after catch_all");
} else if (EHInstStack.back() == TRY) {
if (EHPadStack.empty() || DelegateStack.empty()) {
if (EHPadStack.empty()) {
printAnnotation(OS, "try-catch mismatch!");
} else {
printAnnotation(OS,
"catch" + utostr(EHPadStack.pop_back_val()) + ':');
DelegateStack.pop_back();
}
EHInstStack.pop_back();
if (Opc == WebAssembly::CATCH || Opc == WebAssembly::CATCH_S) {
Expand All @@ -184,26 +178,28 @@ void WebAssemblyInstPrinter::printInst(const MCInst *MI, uint64_t Address,
case WebAssembly::DELEGATE:
case WebAssembly::DELEGATE_S:
if (ControlFlowStack.empty() || EHPadStack.empty() ||
DelegateStack.empty() || EHInstStack.empty()) {
EHInstStack.empty()) {
printAnnotation(OS, "try-delegate mismatch!");
} else {
// 'delegate' is
// 1. A marker for the end of block label
// 2. A destination for throwing instructions
// 3. An instruction that itself rethrows to another 'catch'
assert(ControlFlowStack.back().first == EHPadStack.back() &&
EHPadStack.back() == DelegateStack.back());
assert(ControlFlowStack.back().first == EHPadStack.back());
std::string Label = "label/catch" +
utostr(ControlFlowStack.pop_back_val().first) +
": ";
EHPadStack.pop_back();
DelegateStack.pop_back();
EHInstStack.pop_back();
uint64_t Depth = MI->getOperand(0).getImm();
if (Depth >= DelegateStack.size()) {
if (Depth >= ControlFlowStack.size()) {
Label += "to caller";
} else {
Label += "down to catch" + utostr(DelegateStack.rbegin()[Depth]);
const auto &Pair = ControlFlowStack.rbegin()[Depth];
if (Pair.second)
printAnnotation(OS, "delegate cannot target a loop");
else
Label += "down to catch" + utostr(Pair.first);
}
printAnnotation(OS, Label);
}
Expand Down
5 changes: 0 additions & 5 deletions llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyInstPrinter.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -27,11 +27,6 @@ class WebAssemblyInstPrinter final : public MCInstPrinter {
uint64_t ControlFlowCounter = 0;
SmallVector<std::pair<uint64_t, bool>, 4> ControlFlowStack;
SmallVector<uint64_t, 4> EHPadStack;
// 'delegate' can target any block-like structure, but in case the target is
// 'try', it rethrows to the corresponding 'catch'. Because it can target all
// blocks but with a slightly different semantics with branches, we need a
// separate stack for 'delegate'.
SmallVector<uint64_t, 4> DelegateStack;

enum EHInstKind { TRY, CATCH, CATCH_ALL };
SmallVector<EHInstKind, 4> EHInstStack;
Expand Down
105 changes: 65 additions & 40 deletions llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -80,8 +80,12 @@ class WebAssemblyCFGStackify final : public MachineFunctionPass {
void removeUnnecessaryInstrs(MachineFunction &MF);

// Wrap-up
unsigned getDepth(const SmallVectorImpl<const MachineBasicBlock *> &Stack,
const MachineBasicBlock *MBB);
using EndMarkerInfo =
std::pair<const MachineBasicBlock *, const MachineInstr *>;
unsigned getBranchDepth(const SmallVectorImpl<EndMarkerInfo> &Stack,
const MachineBasicBlock *MBB);
unsigned getDelegateDepth(const SmallVectorImpl<EndMarkerInfo> &Stack,
const MachineBasicBlock *MBB);
void rewriteDepthImmediates(MachineFunction &MF);
void fixEndsAtEndOfFunction(MachineFunction &MF);
void cleanupFunctionData(MachineFunction &MF);
Expand Down Expand Up @@ -1399,21 +1403,6 @@ void WebAssemblyCFGStackify::recalculateScopeTops(MachineFunction &MF) {
}
}

unsigned WebAssemblyCFGStackify::getDepth(
const SmallVectorImpl<const MachineBasicBlock *> &Stack,
const MachineBasicBlock *MBB) {
if (MBB == FakeCallerBB)
return Stack.size();
unsigned Depth = 0;
for (auto X : reverse(Stack)) {
if (X == MBB)
break;
++Depth;
}
assert(Depth < Stack.size() && "Branch destination should be in scope");
return Depth;
}

/// In normal assembly languages, when the end of a function is unreachable,
/// because the function ends in an infinite loop or a noreturn call or similar,
/// it isn't necessary to worry about the function return type at the end of
Expand Down Expand Up @@ -1515,48 +1504,85 @@ void WebAssemblyCFGStackify::placeMarkers(MachineFunction &MF) {
}
}

unsigned WebAssemblyCFGStackify::getBranchDepth(
const SmallVectorImpl<EndMarkerInfo> &Stack, const MachineBasicBlock *MBB) {
unsigned Depth = 0;
for (auto X : reverse(Stack)) {
if (X.first == MBB)
break;
++Depth;
}
assert(Depth < Stack.size() && "Branch destination should be in scope");
return Depth;
}

unsigned WebAssemblyCFGStackify::getDelegateDepth(
const SmallVectorImpl<EndMarkerInfo> &Stack, const MachineBasicBlock *MBB) {
if (MBB == FakeCallerBB)
return Stack.size();
// Delegate's destination is either a catch or a another delegate BB. When the
// destination is another delegate, we can compute the argument in the same
// way as branches, because the target delegate BB only contains the single
// delegate instruction.
if (!MBB->isEHPad()) // Target is a delegate BB
return getBranchDepth(Stack, MBB);

// When the delegate's destination is a catch BB, we need to use its
// corresponding try's end_try BB because Stack contains each marker's end BB.
// Also we need to check if the end marker instruction matches, because a
// single BB can contain multiple end markers, like this:
// bb:
// END_BLOCK
// END_TRY
// END_BLOCK
// END_TRY
// ...
//
// In case of branches getting the immediate that targets any of these is
// fine, but delegate has to exactly target the correct try.
unsigned Depth = 0;
const MachineInstr *EndTry = BeginToEnd[EHPadToTry[MBB]];
for (auto X : reverse(Stack)) {
if (X.first == EndTry->getParent() && X.second == EndTry)
break;
++Depth;
}
assert(Depth < Stack.size() && "Delegate destination should be in scope");
return Depth;
}

void WebAssemblyCFGStackify::rewriteDepthImmediates(MachineFunction &MF) {
// Now rewrite references to basic blocks to be depth immediates.
SmallVector<const MachineBasicBlock *, 8> Stack;
SmallVector<const MachineBasicBlock *, 8> DelegateStack;
SmallVector<EndMarkerInfo, 8> Stack;
for (auto &MBB : reverse(MF)) {
for (auto I = MBB.rbegin(), E = MBB.rend(); I != E; ++I) {
MachineInstr &MI = *I;
switch (MI.getOpcode()) {
case WebAssembly::BLOCK:
case WebAssembly::TRY:
assert(ScopeTops[Stack.back()->getNumber()]->getNumber() <=
assert(ScopeTops[Stack.back().first->getNumber()]->getNumber() <=
MBB.getNumber() &&
"Block/try marker should be balanced");
Stack.pop_back();
DelegateStack.pop_back();
break;

case WebAssembly::LOOP:
assert(Stack.back() == &MBB && "Loop top should be balanced");
assert(Stack.back().first == &MBB && "Loop top should be balanced");
Stack.pop_back();
DelegateStack.pop_back();
break;

case WebAssembly::END_BLOCK:
Stack.push_back(&MBB);
DelegateStack.push_back(&MBB);
Stack.push_back(std::make_pair(&MBB, &MI));
break;

case WebAssembly::END_TRY:
// We handle DELEGATE in the default level, because DELEGATE has
// immediate operands to rewirte.
Stack.push_back(&MBB);
// immediate operands to rewrite.
Stack.push_back(std::make_pair(&MBB, &MI));
break;

case WebAssembly::END_LOOP:
Stack.push_back(EndToBegin[&MI]->getParent());
DelegateStack.push_back(EndToBegin[&MI]->getParent());
break;

case WebAssembly::CATCH:
case WebAssembly::CATCH_ALL:
DelegateStack.push_back(&MBB);
Stack.push_back(std::make_pair(EndToBegin[&MI]->getParent(), &MI));
break;

default:
Expand All @@ -1569,18 +1595,17 @@ void WebAssemblyCFGStackify::rewriteDepthImmediates(MachineFunction &MF) {
if (MO.isMBB()) {
if (MI.getOpcode() == WebAssembly::DELEGATE)
MO = MachineOperand::CreateImm(
getDepth(DelegateStack, MO.getMBB()));
getDelegateDepth(Stack, MO.getMBB()));
else
MO = MachineOperand::CreateImm(getDepth(Stack, MO.getMBB()));
MO = MachineOperand::CreateImm(
getBranchDepth(Stack, MO.getMBB()));
}
MI.addOperand(MF, MO);
}
}

if (MI.getOpcode() == WebAssembly::DELEGATE) {
Stack.push_back(&MBB);
DelegateStack.push_back(&MBB);
}
if (MI.getOpcode() == WebAssembly::DELEGATE)
Stack.push_back(std::make_pair(&MBB, &MI));
break;
}
}
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
View file
Original file line number Diff line number Diff line change
Expand Up @@ -658,7 +658,7 @@ try.cont: ; preds = %catch.start0
; --- try-delegate starts (call unwind mismatch)
; NOSORT: try
; NOSORT: call __cxa_end_catch
; NOSORT: delegate 2 # label/catch{{[0-9]+}}: to caller
; NOSORT: delegate 3 # label/catch{{[0-9]+}}: to caller
; --- try-delegate ends (call unwind mismatch)
; NOSORT: end_try
; NOSORT: delegate 1 # label/catch{{[0-9]+}}: to caller
Expand Down

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