[WebAssembly] Delete ThrowUnwindDest map from WasmEHFuncInfo

Summary:
Before when we implemented the first EH proposal, 'catch <tag>'
instruction may not catch an exception so there were multiple EH pads an
exception can unwind to. That means a BB could have multiple EH pad
successors.

Now after we switched to the new proposal, every 'catch' instruction
catches an exception, and there is only one catchpad per catchswitch, so
we at most have one EH pad successor, making `ThrowUnwindDest` map in
`WasmEHInfo` unnecessary.

Keeping `ThrowUnwindDest` map in `WasmEHInfo` has its own problems,
because other optimization passes can split a BB that contains possibly
throwing calls (previously invokes), and we have to update the map every
time that happens, which is not easy for common CodeGen passes.

This also correctly updates successor info in LateEHPrepare when we add
a rethrow instruction.

Reviewers: dschuff

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58486

llvm-svn: 355296

llvm/include/llvm/CodeGen/WasmEHFuncInfo.h

@@ -28,10 +28,6 @@ struct WasmEHFuncInfo {
   // When there is an entry <A, B>, if an exception is not caught by A, it
   // should next unwind to the EH pad B.
   DenseMap<BBOrMBB, BBOrMBB> EHPadUnwindMap;
-  // For entry <A, B>, A is a BB with an instruction that may throw
-  // (invoke/cleanupret in LLVM IR, call/rethrow in the backend) and B is an EH
-  // pad that A unwinds to.
-  DenseMap<BBOrMBB, BBOrMBB> ThrowUnwindMap;
 
   // Helper functions
   const BasicBlock *getEHPadUnwindDest(const BasicBlock *BB) const {
@@ -40,37 +36,19 @@ struct WasmEHFuncInfo {
   void setEHPadUnwindDest(const BasicBlock *BB, const BasicBlock *Dest) {
     EHPadUnwindMap[BB] = Dest;
   }
-  const BasicBlock *getThrowUnwindDest(BasicBlock *BB) const {
-    return ThrowUnwindMap.lookup(BB).get<const BasicBlock *>();
-  }
-  void setThrowUnwindDest(const BasicBlock *BB, const BasicBlock *Dest) {
-    ThrowUnwindMap[BB] = Dest;
-  }
   bool hasEHPadUnwindDest(const BasicBlock *BB) const {
     return EHPadUnwindMap.count(BB);
   }
-  bool hasThrowUnwindDest(const BasicBlock *BB) const {
-    return ThrowUnwindMap.count(BB);
-  }
 
   MachineBasicBlock *getEHPadUnwindDest(MachineBasicBlock *MBB) const {
     return EHPadUnwindMap.lookup(MBB).get<MachineBasicBlock *>();
   }
   void setEHPadUnwindDest(MachineBasicBlock *MBB, MachineBasicBlock *Dest) {
     EHPadUnwindMap[MBB] = Dest;
   }
-  MachineBasicBlock *getThrowUnwindDest(MachineBasicBlock *MBB) const {
-    return ThrowUnwindMap.lookup(MBB).get<MachineBasicBlock *>();
-  }
-  void setThrowUnwindDest(MachineBasicBlock *MBB, MachineBasicBlock *Dest) {
-    ThrowUnwindMap[MBB] = Dest;
-  }
   bool hasEHPadUnwindDest(MachineBasicBlock *MBB) const {
     return EHPadUnwindMap.count(MBB);
   }
-  bool hasThrowUnwindDest(MachineBasicBlock *MBB) const {
-    return ThrowUnwindMap.count(MBB);
-  }
 };
 
 // Analyze the IR in the given function to build WasmEHFuncInfo.

llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp

@@ -321,13 +321,6 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
       NewMap[MBBMap[Src]] = MBBMap[Dst];
     }
     EHInfo.EHPadUnwindMap = std::move(NewMap);
-    NewMap.clear();
-    for (auto &KV : EHInfo.ThrowUnwindMap) {
-      const auto *Src = KV.first.get<const BasicBlock *>();
-      const auto *Dst = KV.second.get<const BasicBlock *>();
-      NewMap[MBBMap[Src]] = MBBMap[Dst];
-    }
-    EHInfo.ThrowUnwindMap = std::move(NewMap);
   }
 }
 

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -1684,6 +1684,8 @@ static void findUnwindDestinations(
 
   if (IsWasmCXX) {
     findWasmUnwindDestinations(FuncInfo, EHPadBB, Prob, UnwindDests);
+    assert(UnwindDests.size() <= 1 &&
+           "There should be at most one unwind destination for wasm");
     return;
   }
 

llvm/lib/CodeGen/WasmEHPrepare.cpp

@@ -376,22 +376,4 @@ 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);
-  }
 }

llvm/lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp

@@ -330,7 +330,7 @@ bool WebAssemblyLateEHPrepare::addExceptionExtraction(MachineFunction &MF) {
     } else {
       BuildMI(ElseMBB, DL, TII.get(WebAssembly::RETHROW));
       if (EHInfo->hasEHPadUnwindDest(EHPad))
-        EHInfo->setThrowUnwindDest(ElseMBB, EHInfo->getEHPadUnwindDest(EHPad));
+        ElseMBB->addSuccessor(EHInfo->getEHPadUnwindDest(EHPad));
     }
   }
 

llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll

@@ -105,7 +105,7 @@ try.cont:                                         ; preds = %entry, %catch, %cat
 ; CHECK:             i32.call  $drop=, __cxa_begin_catch
 ; CHECK:             try
 ; CHECK:               call      foo
-; CHECK:               br        2                     # 2: down to label10
+; CHECK:               br        2                     # 2: down to label9
 ; CHECK:             catch
 ; CHECK:               call      __cxa_end_catch
 ; CHECK:               rethrow                         # down to catch3
@@ -116,7 +116,7 @@ try.cont:                                         ; preds = %entry, %catch, %cat
 ; CHECK:         catch     {{.*}}                      # catch3:
 ; CHECK:           call      __cxa_end_catch
 ; CHECK:           rethrow                             # to caller
-; CHECK:         end_try                               # label10:
+; CHECK:         end_try                               # label9:
 ; CHECK:         call      __cxa_end_catch
 ; CHECK:         br        2                           # 2: down to label6
 ; CHECK:       end_try