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[WebAssembly] Fix ExceptionInfo grouping again

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This is a case D97677 missed. When taking out remaining BBs that are
reachable from already-taken-out exceptions (because they are not
subexcptions but unwind destinations), I assumed the remaining BBs are
not EH pads, but they can be. For example,
```
try {
  try {
    throw 0;
  } catch (int) { // (a)
  }
} catch (int) {   // (b)
}
try {
  foo();
} catch (int) {   // (c)
}
```
In this code, (b) is the unwind destination of (a) so its exception is
taken out of (a)'s exception, But even though the next try-catch is not
inside the first two-level try-catches, because the first try always
throws, its continuation BB is unreachable and the whole rest of the
function is dominated by EH pad (a), including EH pad (c). So after we
take out of (b)'s exception out of (a)'s, we also need to take out (c)'s
exception out of (a)'s, because (c) is reachable from (b).

This adds one more step before what we did for remaining BBs in D97677;
it traverses EH pads first to take subexceptions out of their incorrect
parent exception. It's the same thing as D97677, but because we can do
this before we add BBs to exceptions' sets, we don't need to fix sets
and only need to fix parent exception pointers.

Other changes are variable name changes (I changed `WE` -> `SrcWE`,
`UnwindWE` -> `DstWE` for clarity), some comment changes, and a drive-by
fix in a bug in a `LLVM_DEBUG` print statement.

Fixes https://github.com/emscripten-core/emscripten/issues/13588.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D97929
This commit is contained in:
Heejin Ahn 2021-03-04 02:14:23 -08:00
parent e39ae82bd1
commit f1f186931b
2 changed files with 180 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

118
lib/Target/WebAssembly/WebAssemblyExceptionInfo.cpp
View File

@ -120,7 +120,8 @@ void WebAssemblyExceptionInfo::recalculate(
// and A's unwind destination is B and B's is C. When we visit B before A, we
// end up extracting C only out of B but not out of A.
const auto *EHInfo = MF.getWasmEHFuncInfo();
DenseMap<WebAssemblyException *, WebAssemblyException *> UnwindWEMap;
SmallVector<std::pair<WebAssemblyException *, WebAssemblyException *>>
UnwindWEVec;
for (auto *DomNode : depth_first(&MDT)) {
MachineBasicBlock *EHPad = DomNode->getBlock();
if (!EHPad->isEHPad())
@ -128,30 +129,20 @@ void WebAssemblyExceptionInfo::recalculate(
if (!EHInfo->hasUnwindDest(EHPad))
continue;
auto *UnwindDest = EHInfo->getUnwindDest(EHPad);
auto *WE = getExceptionFor(EHPad);
auto *UnwindWE = getExceptionFor(UnwindDest);
if (WE->contains(UnwindWE)) {
UnwindWEMap[WE] = UnwindWE;
LLVM_DEBUG(dbgs() << "ExceptionInfo fix: " << WE->getEHPad()->getNumber()
<< "." << WE->getEHPad()->getName()
auto *SrcWE = getExceptionFor(EHPad);
auto *DstWE = getExceptionFor(UnwindDest);
if (SrcWE->contains(DstWE)) {
UnwindWEVec.push_back(std::make_pair(SrcWE, DstWE));
LLVM_DEBUG(dbgs() << "Unwind destination ExceptionInfo fix:\n "
<< DstWE->getEHPad()->getNumber() << "."
<< DstWE->getEHPad()->getName()
<< "'s exception is taken out of "
<< UnwindWE->getEHPad()->getNumber() << "."
<< UnwindWE->getEHPad()->getName() << "'s exception\n");
if (WE->getParentException())
UnwindWE->setParentException(WE->getParentException());
else
UnwindWE->setParentException(nullptr);
<< SrcWE->getEHPad()->getNumber() << "."
<< SrcWE->getEHPad()->getName() << "'s exception\n");
DstWE->setParentException(SrcWE->getParentException());
}
}
// Add BBs to exceptions' block set first
for (auto *DomNode : post_order(&MDT)) {
MachineBasicBlock *MBB = DomNode->getBlock();
WebAssemblyException *WE = getExceptionFor(MBB);
for (; WE; WE = WE->getParentException())
WE->addToBlocksSet(MBB);
}
// After fixing subexception relationship between unwind destinations above,
// there can still be remaining discrepancies.
//
@ -161,31 +152,72 @@ void WebAssemblyExceptionInfo::recalculate(
// subexception of Exception A, and we fix it by taking Exception B out of
// Exception A above. But there can still be remaining BBs within Exception A
// that are reachable from Exception B. These BBs semantically don't belong
// to Exception A and were not a part of 'catch' clause or cleanup code in the
// original code, but they just happened to be grouped within Exception A
// because they were dominated by EHPad A. We fix this case by taking those
// to Exception A and were not a part of this 'catch' clause or cleanup code
// in the original code, but they just happened to be grouped within Exception
// A because they were dominated by EHPad A. We fix this case by taking those
// BBs out of the incorrect exception and all its subexceptions that it
// belongs to.
for (auto &KV : UnwindWEMap) {
WebAssemblyException *WE = KV.first;
WebAssemblyException *UnwindWE = KV.second;
//
// 1. First, we take out remaining incorrect subexceptions. This part is
// easier, because we haven't added BBs to exceptions yet, we only need to
// change parent exception pointer.
for (auto *DomNode : depth_first(&MDT)) {
MachineBasicBlock *EHPad = DomNode->getBlock();
if (!EHPad->isEHPad())
continue;
auto *WE = getExceptionFor(EHPad);
for (auto *MBB : WE->getBlocksSet()) {
// For each source EHPad -> unwind destination EHPad
for (auto &P : UnwindWEVec) {
auto *SrcWE = P.first;
auto *DstWE = P.second;
// If WE (the current EH pad's exception) is still contained in SrcWE but
// reachable from DstWE that was taken out of SrcWE above, we have to take
// out WE out of SrcWE too.
if (WE != SrcWE && SrcWE->contains(WE) && !DstWE->contains(WE) &&
isReachableAmongDominated(DstWE->getEHPad(), EHPad, SrcWE->getEHPad(),
MDT)) {
LLVM_DEBUG(dbgs() << "Remaining reachable ExceptionInfo fix:\n "
<< WE->getEHPad()->getNumber() << "."
<< WE->getEHPad()->getName()
<< "'s exception is taken out of "
<< SrcWE->getEHPad()->getNumber() << "."
<< SrcWE->getEHPad()->getName() << "'s exception\n");
WE->setParentException(SrcWE->getParentException());
}
}
}
// Add BBs to exceptions' block set. This is a preparation to take out
// remaining incorect BBs from exceptions, because we need to iterate over BBs
// for each exception.
for (auto *DomNode : post_order(&MDT)) {
MachineBasicBlock *MBB = DomNode->getBlock();
WebAssemblyException *WE = getExceptionFor(MBB);
for (; WE; WE = WE->getParentException())
WE->addToBlocksSet(MBB);
}
// 2. We take out remaining individual BBs out. Now we have added BBs to each
// exceptions' BlockSet, when we take a BB out of an exception, we need to fix
// those sets too.
for (auto &P : UnwindWEVec) {
auto *SrcWE = P.first;
auto *DstWE = P.second;
for (auto *MBB : SrcWE->getBlocksSet()) {
if (MBB->isEHPad()) {
// If this assertion is triggered, it would be a violation of scoping
// rules in ll files, because this means an instruction in an outer
// scope tries to unwind to an EH pad in an inner scope.
assert(!isReachableAmongDominated(UnwindWE->getEHPad(), MBB,
WE->getEHPad(), MDT) &&
"Outer scope unwinds to inner scope. Bug in scope rules?");
assert(!isReachableAmongDominated(DstWE->getEHPad(), MBB,
SrcWE->getEHPad(), MDT) &&
"We already handled EH pads above");
continue;
}
if (isReachableAmongDominated(UnwindWE->getEHPad(), MBB, WE->getEHPad(),
if (isReachableAmongDominated(DstWE->getEHPad(), MBB, SrcWE->getEHPad(),
MDT)) {
LLVM_DEBUG(dbgs() << "Remainder BB: " << MBB->getNumber() << "."
<< MBB->getName() << " is ");
<< MBB->getName() << " is\n");
WebAssemblyException *InnerWE = getExceptionFor(MBB);
while (InnerWE != WE) {
while (InnerWE != SrcWE) {
LLVM_DEBUG(dbgs()
<< " removed from " << InnerWE->getEHPad()->getNumber()
<< "." << InnerWE->getEHPad()->getName()
@ -193,13 +225,13 @@ void WebAssemblyExceptionInfo::recalculate(
InnerWE->removeFromBlocksSet(MBB);
InnerWE = InnerWE->getParentException();
}
WE->removeFromBlocksSet(MBB);
LLVM_DEBUG(dbgs() << " removed from " << WE->getEHPad()->getNumber()
<< "." << WE->getEHPad()->getName()
SrcWE->removeFromBlocksSet(MBB);
LLVM_DEBUG(dbgs() << " removed from " << SrcWE->getEHPad()->getNumber()
<< "." << SrcWE->getEHPad()->getName()
<< "'s exception\n");
changeExceptionFor(MBB, WE->getParentException());
if (WE->getParentException())
WE->getParentException()->addToBlocksSet(MBB);
changeExceptionFor(MBB, SrcWE->getParentException());
if (SrcWE->getParentException())
SrcWE->getParentException()->addToBlocksSet(MBB);
}
}
}

105
test/CodeGen/WebAssembly/cfg-stackify-eh.ll
View File

@ -1537,6 +1537,111 @@ unreachable: ; preds = %rethrow, %rethrow6
unreachable
}
; void test25() {
; try {
; try {
; throw 0;
; } catch (int) { // (a)
; }
; } catch (int) { // (b)
; }
; try {
; foo();
; } catch (int) { // (c)
; }
; }
;
; Regression test for an ExceptionInfo grouping bug. Because the first (inner)
; try always throws, both EH pads (b) (catch.start2) and (c) (catch.start10) are
; dominated by EH pad (a) (catch.start), even though they are not semantically
; contained in (a)'s exception. Because (a)'s unwind destination is (b), (b)'s
; exception is taken out of (a)'s. But because (c) is reachable from (b), we
; should make sure to take out (c)'s exception out of (a)'s exception too.
define void @test25() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
%exception = call i8* @__cxa_allocate_exception(i32 4) #1
%0 = bitcast i8* %exception to i32*
store i32 0, i32* %0, align 16
invoke void @__cxa_throw(i8* %exception, i8* bitcast (i8** @_ZTIi to i8*), i8* null) #3
to label %unreachable unwind label %catch.dispatch
catch.dispatch: ; preds = %entry
%1 = catchswitch within none [label %catch.start] unwind label %catch.dispatch1
catch.start: ; preds = %catch.dispatch
%2 = catchpad within %1 [i8* bitcast (i8** @_ZTIi to i8*)]
%3 = call i8* @llvm.wasm.get.exception(token %2)
%4 = call i32 @llvm.wasm.get.ehselector(token %2)
%5 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*)) #1
%matches = icmp eq i32 %4, %5
br i1 %matches, label %catch, label %rethrow
catch: ; preds = %catch.start
%6 = call i8* @__cxa_begin_catch(i8* %3) #1 [ "funclet"(token %2) ]
%7 = bitcast i8* %6 to i32*
%8 = load i32, i32* %7, align 4
call void @__cxa_end_catch() #1 [ "funclet"(token %2) ]
catchret from %2 to label %try.cont8
rethrow: ; preds = %catch.start
invoke void @llvm.wasm.rethrow() #3 [ "funclet"(token %2) ]
to label %unreachable unwind label %catch.dispatch1
catch.dispatch1: ; preds = %rethrow, %catch.dispatch
%9 = catchswitch within none [label %catch.start2] unwind to caller
catch.start2: ; preds = %catch.dispatch1
%10 = catchpad within %9 [i8* bitcast (i8** @_ZTIi to i8*)]
%11 = call i8* @llvm.wasm.get.exception(token %10)
%12 = call i32 @llvm.wasm.get.ehselector(token %10)
%13 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*)) #1
%matches3 = icmp eq i32 %12, %13
br i1 %matches3, label %catch5, label %rethrow4
catch5: ; preds = %catch.start2
%14 = call i8* @__cxa_begin_catch(i8* %11) #1 [ "funclet"(token %10) ]
%15 = bitcast i8* %14 to i32*
%16 = load i32, i32* %15, align 4
call void @__cxa_end_catch() #1 [ "funclet"(token %10) ]
catchret from %10 to label %try.cont8
rethrow4: ; preds = %catch.start2
call void @llvm.wasm.rethrow() #3 [ "funclet"(token %10) ]
unreachable
try.cont8: ; preds = %catch, %catch5
invoke void @foo()
to label %try.cont16 unwind label %catch.dispatch9
catch.dispatch9: ; preds = %try.cont8
%17 = catchswitch within none [label %catch.start10] unwind to caller
catch.start10: ; preds = %catch.dispatch9
%18 = catchpad within %17 [i8* bitcast (i8** @_ZTIi to i8*)]
%19 = call i8* @llvm.wasm.get.exception(token %18)
%20 = call i32 @llvm.wasm.get.ehselector(token %18)
%21 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*)) #1
%matches11 = icmp eq i32 %20, %21
br i1 %matches11, label %catch13, label %rethrow12
catch13: ; preds = %catch.start10
%22 = call i8* @__cxa_begin_catch(i8* %19) #1 [ "funclet"(token %18) ]
%23 = bitcast i8* %22 to i32*
%24 = load i32, i32* %23, align 4
call void @__cxa_end_catch() #1 [ "funclet"(token %18) ]
catchret from %18 to label %try.cont16
rethrow12: ; preds = %catch.start10
call void @llvm.wasm.rethrow() #3 [ "funclet"(token %18) ]
unreachable
try.cont16: ; preds = %try.cont8, %catch13
ret void
unreachable: ; preds = %rethrow, %entry
unreachable
}
; Check if the unwind destination mismatch stats are correct
; NOSORT: 23 wasm-cfg-stackify - Number of call unwind mismatches found
; NOSORT: 4 wasm-cfg-stackify - Number of catch unwind mismatches found