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[WebAssembly] Fix remapping branch dests in fixCatchUnwindMismatches
This is a case D97178 tried to solve but missed. D97178 could not handle
the case when
multiple consecutive delegates are generated:
- Before:
```
block
br (a)
try
catch
end_try
end_block
<- (a)
```
- After
```
block
br (a)
try
...
try
try
catch
end_try
<- (a)
delegate
delegate
end_block
<- (b)
```
(The `br` should point to (b) now)
D97178 assumed `end_block` exists two BBs later than `end_try`, because
it assumed the order as `end_try` BB -> `delegate` BB -> `end_block` BB.
But it turned out there can be multiple `delegate`s in between. This
patch changes the logic so we just search from `end_try` BB until we
find `end_block`.
Fixes https://github.com/emscripten-core/emscripten/issues/13515.
(More precisely, fixes
https://github.com/emscripten-core/emscripten/issues/13515#issuecomment-784711318.)
Reviewed By: dschuff, tlively
Differential Revision: https://reviews.llvm.org/D97569
This commit is contained in:
Heejin Ahn
parent
2152c1de23
commit
52b47abf91
@ -1368,9 +1368,7 @@ bool WebAssemblyCFGStackify::fixCatchUnwindMismatches(MachineFunction &MF) {
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if (EHPadToUnwindDest.empty())
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return false;
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NumCatchUnwindMismatches += EHPadToUnwindDest.size();
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// <current branch dest, future branch dest> map, because fixing catch unwind
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// mismatches can invalidate branch destinations
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DenseMap<MachineBasicBlock *, MachineBasicBlock *> BrDestMap;
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SmallPtrSet<MachineBasicBlock *, 4> NewEndTryBBs;
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for (auto &P : EHPadToUnwindDest) {
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MachineBasicBlock *EHPad = P.first;
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@ -1378,8 +1376,7 @@ bool WebAssemblyCFGStackify::fixCatchUnwindMismatches(MachineFunction &MF) {
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MachineInstr *Try = EHPadToTry[EHPad];
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MachineInstr *EndTry = BeginToEnd[Try];
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addTryDelegate(Try, EndTry, UnwindDest);
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BrDestMap[EndTry->getParent()] =
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EndTry->getParent()->getNextNode()->getNextNode();
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NewEndTryBBs.insert(EndTry->getParent());
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}
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// Adding a try-delegate wrapping an existing try-catch-end can make existing
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@ -1423,17 +1420,29 @@ bool WebAssemblyCFGStackify::fixCatchUnwindMismatches(MachineFunction &MF) {
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// As we can see in this case, when branches target a BB that has both
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// 'end_try' and 'end_block' and the BB is split to insert a 'delegate', we
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// have to remap existing branch destinations so that they target not the
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// 'end_try' BB but the new 'end_block' BB, which should be the second next BB
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// of 'end_try' (because there is a 'delegate' BB in between). In this
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// example, the 'br bb3' instruction should be remapped to 'br split_bb'.
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// 'end_try' BB but the new 'end_block' BB. There can be multiple 'delegate's
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// in between, so we try to find the next BB with 'end_block' instruction. In
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// this example, the 'br bb3' instruction should be remapped to 'br split_bb'.
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for (auto &MBB : MF) {
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for (auto &MI : MBB) {
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if (MI.isTerminator()) {
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for (auto &MO : MI.operands()) {
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if (MO.isMBB()) {
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auto It = BrDestMap.find(MO.getMBB());
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if (It != BrDestMap.end())
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MO.setMBB(It->second);
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if (MO.isMBB() && NewEndTryBBs.count(MO.getMBB())) {
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auto *BrDest = MO.getMBB();
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bool FoundEndBlock = false;
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for (; std::next(BrDest->getIterator()) != MF.end();
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BrDest = BrDest->getNextNode()) {
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for (const auto &MI : *BrDest) {
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if (MI.getOpcode() == WebAssembly::END_BLOCK) {
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FoundEndBlock = true;
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break;
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}
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}
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if (FoundEndBlock)
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break;
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}
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assert(FoundEndBlock);
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MO.setMBB(BrDest);
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}
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}
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}
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@ -1196,6 +1196,108 @@ try.cont: ; preds = %catch.start1, %catc
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ret void
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}
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; The similar case with test20, but multiple consecutive delegates are
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; generated:
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; - Before:
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; block
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; br (a)
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; try
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; catch
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; end_try
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; end_block
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; <- (a)
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;
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; - After
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; block
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; br (a)
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; try
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; ...
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; try
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; try
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; catch
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; end_try
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; <- (a)
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; delegate
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; delegate
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; end_block
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; <- (b) The br destination should be remapped to here
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;
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; The test was reduced by bugpoint and should not crash.
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define void @test21() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
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entry:
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br i1 undef, label %if.then, label %if.end12
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if.then: ; preds = %entry
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invoke void @__cxa_throw() #1
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to label %unreachable unwind label %catch.dispatch
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catch.dispatch: ; preds = %if.then
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%0 = catchswitch within none [label %catch.start] unwind to caller
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catch.start: ; preds = %catch.dispatch
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%1 = catchpad within %0 [i8* bitcast (i8** @_ZTIi to i8*)]
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%2 = call i8* @llvm.wasm.get.exception(token %1)
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%3 = call i32 @llvm.wasm.get.ehselector(token %1)
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catchret from %1 to label %catchret.dest
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catchret.dest: ; preds = %catch.start
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invoke void @foo()
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to label %invoke.cont unwind label %catch.dispatch4
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invoke.cont: ; preds = %catchret.dest
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invoke void @__cxa_throw() #1
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to label %unreachable unwind label %catch.dispatch4
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catch.dispatch4: ; preds = %invoke.cont, %catchret.dest
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%4 = catchswitch within none [label %catch.start5] unwind to caller
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catch.start5: ; preds = %catch.dispatch4
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%5 = catchpad within %4 [i8* bitcast (i8** @_ZTIi to i8*)]
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%6 = call i8* @llvm.wasm.get.exception(token %5)
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%7 = call i32 @llvm.wasm.get.ehselector(token %5)
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unreachable
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if.end12: ; preds = %entry
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invoke void @foo()
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to label %invoke.cont14 unwind label %catch.dispatch16
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catch.dispatch16: ; preds = %if.end12
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%8 = catchswitch within none [label %catch.start17] unwind label %ehcleanup
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catch.start17: ; preds = %catch.dispatch16
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%9 = catchpad within %8 [i8* bitcast (i8** @_ZTIi to i8*)]
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%10 = call i8* @llvm.wasm.get.exception(token %9)
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%11 = call i32 @llvm.wasm.get.ehselector(token %9)
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br i1 undef, label %catch20, label %rethrow19
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catch20: ; preds = %catch.start17
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catchret from %9 to label %catchret.dest22
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catchret.dest22: ; preds = %catch20
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br label %try.cont23
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rethrow19: ; preds = %catch.start17
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invoke void @llvm.wasm.rethrow() #1 [ "funclet"(token %9) ]
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to label %unreachable unwind label %ehcleanup
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try.cont23: ; preds = %invoke.cont14, %catchret.dest22
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invoke void @foo()
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to label %invoke.cont24 unwind label %ehcleanup
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invoke.cont24: ; preds = %try.cont23
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ret void
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invoke.cont14: ; preds = %if.end12
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br label %try.cont23
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ehcleanup: ; preds = %try.cont23, %rethrow19, %catch.dispatch16
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%12 = cleanuppad within none []
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cleanupret from %12 unwind to caller
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unreachable: ; preds = %if.then, %invoke.cont, %rethrow19
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unreachable
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}
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; Check if the unwind destination mismatch stats are correct
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; NOSORT: 20 wasm-cfg-stackify - Number of call unwind mismatches found
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; NOSORT: 4 wasm-cfg-stackify - Number of catch unwind mismatches found
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@ -1225,6 +1327,8 @@ declare i8* @llvm.wasm.get.exception(token) #0
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; Function Attrs: nounwind
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declare i32 @llvm.wasm.get.ehselector(token) #0
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; Function Attrs: noreturn
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declare void @__cxa_throw() #1
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; Function Attrs: noreturn
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declare void @llvm.wasm.rethrow() #1
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; Function Attrs: nounwind
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declare i32 @llvm.eh.typeid.for(i8*) #0
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