Simplify EH control flow by observing that EH scopes form a simple

hierarchy of delegation, and that EH selector values are meaningful
function-wide (good thing, too, or inlining wouldn't work).
2,3d
1a
hierarchy of delegation and that EH selector values have the same
meaning everywhere in the function instead of being meaningful only
in the context of a specific selector.

This removes the need for routing edges through EH cleanups,
since a cleanup simply always branches to its enclosing scope.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@137293 91177308-0d34-0410-b5e6-96231b3b80d8

Author: rjmccall

Diff for: lib/CodeGen/CGCleanup.cpp

@@ -119,16 +119,30 @@ char *EHScopeStack::allocate(size_t Size) {
 }
 
 EHScopeStack::stable_iterator
-EHScopeStack::getEnclosingEHCleanup(iterator it) const {
-  assert(it != end());
-  do {
-    if (isa<EHCleanupScope>(*it)) {
-      if (cast<EHCleanupScope>(*it).isEHCleanup())
-        return stabilize(it);
-      return cast<EHCleanupScope>(*it).getEnclosingEHCleanup();
+EHScopeStack::getInnermostActiveNormalCleanup() const {
+  for (stable_iterator si = getInnermostNormalCleanup(), se = stable_end();
+         si != se; ) {
+    EHCleanupScope &cleanup = cast<EHCleanupScope>(*find(si));
+    if (cleanup.isActive()) return si;
+    si = cleanup.getEnclosingNormalCleanup();
+  }
+  return stable_end();
+}
+
+EHScopeStack::stable_iterator EHScopeStack::getInnermostActiveEHScope() const {
+  for (stable_iterator si = getInnermostEHScope(), se = stable_end();
+         si != se; ) {
+    // Skip over inactive cleanups.
+    EHCleanupScope *cleanup = dyn_cast<EHCleanupScope>(&*find(si));
+    if (cleanup && !cleanup->isActive()) {
+      si = cleanup->getEnclosingEHScope();
+      continue;
     }
-    ++it;
-  } while (it != end());
+
+    // All other scopes are always active.
+    return si;
+  }
+
   return stable_end();
 }
 
@@ -146,11 +160,11 @@ void *EHScopeStack::pushCleanup(CleanupKind Kind, size_t Size) {
                                 Size,
                                 BranchFixups.size(),
                                 InnermostNormalCleanup,
-                                InnermostEHCleanup);
+                                InnermostEHScope);
   if (IsNormalCleanup)
     InnermostNormalCleanup = stable_begin();
   if (IsEHCleanup)
-    InnermostEHCleanup = stable_begin();
+    InnermostEHScope = stable_begin();
 
   return Scope->getCleanupBuffer();
 }
@@ -161,11 +175,9 @@ void EHScopeStack::popCleanup() {
   assert(isa<EHCleanupScope>(*begin()));
   EHCleanupScope &Cleanup = cast<EHCleanupScope>(*begin());
   InnermostNormalCleanup = Cleanup.getEnclosingNormalCleanup();
-  InnermostEHCleanup = Cleanup.getEnclosingEHCleanup();
+  InnermostEHScope = Cleanup.getEnclosingEHScope();
   StartOfData += Cleanup.getAllocatedSize();
 
-  if (empty()) NextEHDestIndex = FirstEHDestIndex;
-
   // Destroy the cleanup.
   Cleanup.~EHCleanupScope();
 
@@ -182,37 +194,35 @@ void EHScopeStack::popCleanup() {
   }
 }
 
-EHFilterScope *EHScopeStack::pushFilter(unsigned NumFilters) {
-  char *Buffer = allocate(EHFilterScope::getSizeForNumFilters(NumFilters));
-  CatchDepth++;
-  return new (Buffer) EHFilterScope(NumFilters);
+EHFilterScope *EHScopeStack::pushFilter(unsigned numFilters) {
+  assert(getInnermostEHScope() == stable_end());
+  char *buffer = allocate(EHFilterScope::getSizeForNumFilters(numFilters));
+  EHFilterScope *filter = new (buffer) EHFilterScope(numFilters);
+  InnermostEHScope = stable_begin();
+  return filter;
 }
 
 void EHScopeStack::popFilter() {
   assert(!empty() && "popping exception stack when not empty");
 
-  EHFilterScope &Filter = cast<EHFilterScope>(*begin());
-  StartOfData += EHFilterScope::getSizeForNumFilters(Filter.getNumFilters());
-
-  if (empty()) NextEHDestIndex = FirstEHDestIndex;
+  EHFilterScope &filter = cast<EHFilterScope>(*begin());
+  StartOfData += EHFilterScope::getSizeForNumFilters(filter.getNumFilters());
 
-  assert(CatchDepth > 0 && "mismatched filter push/pop");
-  CatchDepth--;
+  InnermostEHScope = filter.getEnclosingEHScope();
 }
 
-EHCatchScope *EHScopeStack::pushCatch(unsigned NumHandlers) {
-  char *Buffer = allocate(EHCatchScope::getSizeForNumHandlers(NumHandlers));
-  CatchDepth++;
-  EHCatchScope *Scope = new (Buffer) EHCatchScope(NumHandlers);
-  for (unsigned I = 0; I != NumHandlers; ++I)
-    Scope->getHandlers()[I].Index = getNextEHDestIndex();
-  return Scope;
+EHCatchScope *EHScopeStack::pushCatch(unsigned numHandlers) {
+  char *buffer = allocate(EHCatchScope::getSizeForNumHandlers(numHandlers));
+  EHCatchScope *scope =
+    new (buffer) EHCatchScope(numHandlers, InnermostEHScope);
+  InnermostEHScope = stable_begin();
+  return scope;
 }
 
 void EHScopeStack::pushTerminate() {
   char *Buffer = allocate(EHTerminateScope::getSize());
-  CatchDepth++;
-  new (Buffer) EHTerminateScope(getNextEHDestIndex());
+  new (Buffer) EHTerminateScope(InnermostEHScope);
+  InnermostEHScope = stable_begin();
 }
 
 /// Remove any 'null' fixups on the stack.  However, we can't pop more
@@ -384,17 +394,6 @@ static llvm::BasicBlock *CreateNormalEntry(CodeGenFunction &CGF,
   return Entry;
 }
 
-static llvm::BasicBlock *CreateEHEntry(CodeGenFunction &CGF,
-                                       EHCleanupScope &Scope) {
-  assert(Scope.isEHCleanup());
-  llvm::BasicBlock *Entry = Scope.getEHBlock();
-  if (!Entry) {
-    Entry = CGF.createBasicBlock("eh.cleanup");
-    Scope.setEHBlock(Entry);
-  }
-  return Entry;
-}
-
 /// Attempts to reduce a cleanup's entry block to a fallthrough.  This
 /// is basically llvm::MergeBlockIntoPredecessor, except
 /// simplified/optimized for the tighter constraints on cleanup blocks.
@@ -544,7 +543,10 @@ void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
 
   // Check whether we need an EH cleanup.  This is only true if we've
   // generated a lazy EH cleanup block.
-  bool RequiresEHCleanup = Scope.hasEHBranches();
+  llvm::BasicBlock *EHEntry = Scope.getCachedEHDispatchBlock();
+  assert(Scope.hasEHBranches() == (EHEntry != 0));
+  bool RequiresEHCleanup = (EHEntry != 0);
+  EHScopeStack::stable_iterator EHParent = Scope.getEnclosingEHScope();
 
   // Check the three conditions which might require a normal cleanup:
 
@@ -580,12 +582,6 @@ void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
     RequiresNormalCleanup = true;
   }
 
-  EHScopeStack::Cleanup::Flags cleanupFlags;
-  if (Scope.isNormalCleanup())
-    cleanupFlags.setIsNormalCleanupKind();
-  if (Scope.isEHCleanup())
-    cleanupFlags.setIsEHCleanupKind();
-
   // If we have a prebranched fallthrough into an inactive normal
   // cleanup, rewrite it so that it leads to the appropriate place.
   if (Scope.isNormalCleanup() && HasPrebranchedFallthrough && !IsActive) {
@@ -634,61 +630,11 @@ void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
   EHScopeStack::Cleanup *Fn =
     reinterpret_cast<EHScopeStack::Cleanup*>(CleanupBuffer.data());
 
-  // We want to emit the EH cleanup after the normal cleanup, but go
-  // ahead and do the setup for the EH cleanup while the scope is still
-  // alive.
-  llvm::BasicBlock *EHEntry = 0;
-  SmallVector<llvm::Instruction*, 2> EHInstsToAppend;
-  if (RequiresEHCleanup) {
-    EHEntry = CreateEHEntry(*this, Scope);
-
-    // Figure out the branch-through dest if necessary.
-    llvm::BasicBlock *EHBranchThroughDest = 0;
-    if (Scope.hasEHBranchThroughs()) {
-      assert(Scope.getEnclosingEHCleanup() != EHStack.stable_end());
-      EHScope &S = *EHStack.find(Scope.getEnclosingEHCleanup());
-      EHBranchThroughDest = CreateEHEntry(*this, cast<EHCleanupScope>(S));
-    }
-
-    // If we have exactly one branch-after and no branch-throughs, we
-    // can dispatch it without a switch.
-    if (!Scope.hasEHBranchThroughs() &&
-        Scope.getNumEHBranchAfters() == 1) {
-      assert(!EHBranchThroughDest);
-
-      // TODO: remove the spurious eh.cleanup.dest stores if this edge
-      // never went through any switches.
-      llvm::BasicBlock *BranchAfterDest = Scope.getEHBranchAfterBlock(0);
-      EHInstsToAppend.push_back(llvm::BranchInst::Create(BranchAfterDest));
-    
-    // Otherwise, if we have any branch-afters, we need a switch.
-    } else if (Scope.getNumEHBranchAfters()) {
-      // The default of the switch belongs to the branch-throughs if
-      // they exist.
-      llvm::BasicBlock *Default =
-        (EHBranchThroughDest ? EHBranchThroughDest : getUnreachableBlock());
-
-      const unsigned SwitchCapacity = Scope.getNumEHBranchAfters();
-
-      llvm::LoadInst *Load =
-        new llvm::LoadInst(getEHCleanupDestSlot(), "cleanup.dest");
-      llvm::SwitchInst *Switch =
-        llvm::SwitchInst::Create(Load, Default, SwitchCapacity);
-
-      EHInstsToAppend.push_back(Load);
-      EHInstsToAppend.push_back(Switch);
-
-      for (unsigned I = 0, E = Scope.getNumEHBranchAfters(); I != E; ++I)
-        Switch->addCase(Scope.getEHBranchAfterIndex(I),
-                        Scope.getEHBranchAfterBlock(I));
-
-    // Otherwise, we have only branch-throughs; jump to the next EH
-    // cleanup.
-    } else {
-      assert(EHBranchThroughDest);
-      EHInstsToAppend.push_back(llvm::BranchInst::Create(EHBranchThroughDest));
-    }
-  }
+  EHScopeStack::Cleanup::Flags cleanupFlags;
+  if (Scope.isNormalCleanup())
+    cleanupFlags.setIsNormalCleanupKind();
+  if (Scope.isEHCleanup())
+    cleanupFlags.setIsEHCleanupKind();
 
   if (!RequiresNormalCleanup) {
     destroyOptimisticNormalEntry(*this, Scope);
@@ -890,10 +836,7 @@ void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
     cleanupFlags.setIsForEHCleanup();
     EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag);
 
-    // Append the prepared cleanup prologue from above.
-    llvm::BasicBlock *EHExit = Builder.GetInsertBlock();
-    for (unsigned I = 0, E = EHInstsToAppend.size(); I != E; ++I)
-      EHExit->getInstList().push_back(EHInstsToAppend[I]);
+    Builder.CreateBr(getEHDispatchBlock(EHParent));
 
     Builder.restoreIP(SavedIP);
 
@@ -1005,64 +948,6 @@ void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) {
   Builder.ClearInsertionPoint();
 }
 
-void CodeGenFunction::EmitBranchThroughEHCleanup(UnwindDest Dest) {
-  // We should never get invalid scope depths for an UnwindDest; that
-  // implies that the destination wasn't set up correctly.
-  assert(Dest.getScopeDepth().isValid() && "invalid scope depth on EH dest?");
-
-  if (!HaveInsertPoint())
-    return;
-
-  // Create the branch.
-  llvm::BranchInst *BI = Builder.CreateBr(Dest.getBlock());
-
-  // Calculate the innermost active cleanup.
-  EHScopeStack::stable_iterator
-    InnermostCleanup = EHStack.getInnermostActiveEHCleanup();
-
-  // If the destination is in the same EH cleanup scope as us, we
-  // don't need to thread through anything.
-  if (InnermostCleanup.encloses(Dest.getScopeDepth())) {
-    Builder.ClearInsertionPoint();
-    return;
-  }
-  assert(InnermostCleanup != EHStack.stable_end());
-
-  // Store the index at the start.
-  llvm::ConstantInt *Index = Builder.getInt32(Dest.getDestIndex());
-  new llvm::StoreInst(Index, getEHCleanupDestSlot(), BI);
-
-  // Adjust BI to point to the first cleanup block.
-  {
-    EHCleanupScope &Scope =
-      cast<EHCleanupScope>(*EHStack.find(InnermostCleanup));
-    BI->setSuccessor(0, CreateEHEntry(*this, Scope));
-  }
-  
-  // Add this destination to all the scopes involved.
-  for (EHScopeStack::stable_iterator
-         I = InnermostCleanup, E = Dest.getScopeDepth(); ; ) {
-    assert(E.strictlyEncloses(I));
-    EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.find(I));
-    assert(Scope.isEHCleanup());
-    I = Scope.getEnclosingEHCleanup();
-
-    // If this is the last cleanup we're propagating through, add this
-    // as a branch-after.
-    if (I == E) {
-      Scope.addEHBranchAfter(Index, Dest.getBlock());
-      break;
-    }
-
-    // Otherwise, add it as a branch-through.  If this isn't new
-    // information, all the rest of the work has been done before.
-    if (!Scope.addEHBranchThrough(Dest.getBlock()))
-      break;
-  }
-  
-  Builder.ClearInsertionPoint();
-}
-
 static bool IsUsedAsNormalCleanup(EHScopeStack &EHStack,
                                   EHScopeStack::stable_iterator C) {
   // If we needed a normal block for any reason, that counts.
@@ -1083,18 +968,21 @@ static bool IsUsedAsNormalCleanup(EHScopeStack &EHStack,
 }
 
 static bool IsUsedAsEHCleanup(EHScopeStack &EHStack,
-                              EHScopeStack::stable_iterator C) {
+                              EHScopeStack::stable_iterator cleanup) {
   // If we needed an EH block for any reason, that counts.
-  if (cast<EHCleanupScope>(*EHStack.find(C)).getEHBlock())
+  if (EHStack.find(cleanup)->hasEHBranches())
     return true;
 
   // Check whether any enclosed cleanups were needed.
   for (EHScopeStack::stable_iterator
-         I = EHStack.getInnermostEHCleanup(); I != C; ) {
-    assert(C.strictlyEncloses(I));
-    EHCleanupScope &S = cast<EHCleanupScope>(*EHStack.find(I));
-    if (S.getEHBlock()) return true;
-    I = S.getEnclosingEHCleanup();
+         i = EHStack.getInnermostEHScope(); i != cleanup; ) {
+    assert(cleanup.strictlyEncloses(i));
+
+    EHScope &scope = *EHStack.find(i);
+    if (scope.hasEHBranches())
+      return true;
+
+    i = scope.getEnclosingEHScope();
   }
 
   return false;
@@ -1189,10 +1077,3 @@ llvm::Value *CodeGenFunction::getNormalCleanupDestSlot() {
       CreateTempAlloca(Builder.getInt32Ty(), "cleanup.dest.slot");
   return NormalCleanupDest;
 }
-
-llvm::Value *CodeGenFunction::getEHCleanupDestSlot() {
-  if (!EHCleanupDest)
-    EHCleanupDest =
-      CreateTempAlloca(Builder.getInt32Ty(), "eh.cleanup.dest.slot");
-  return EHCleanupDest;
-}