Teach IR generation how to lazily emit cleanups. This has a lot of advantages,

mostly in avoiding unnecessary work at compile time but also in producing more
sensible block orderings.

Move the destructor cleanups for local variables over to use lazy cleanups.
Eventually all cleanups will do this;  for now we have some awkward code
duplication.

Tell IR generation just to never produce landing pads in -fno-exceptions.
This is a much more comprehensive solution to a problem which previously was
half-solved by checks in most cleanup-generation spots.

llvm-svn: 108270

1 files changed, 177 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 5e505c2d821..eb6c4361be8 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -825,11 +825,168 @@ static void SimplifyCleanupEdges(CodeGenFunction &CGF,
   SimplifyCleanupEntry(CGF, Entry);  
 }
 
+static void EmitLazyCleanup(CodeGenFunction &CGF,
+                            EHScopeStack::LazyCleanup *Fn,
+                            bool ForEH) {
+  if (ForEH) CGF.EHStack.pushTerminate();
+  Fn->Emit(CGF, ForEH);
+  if (ForEH) CGF.EHStack.popTerminate();
+  assert(CGF.HaveInsertPoint() && "cleanup ended with no insertion point?");
+}
+
+static void SplitAndEmitLazyCleanup(CodeGenFunction &CGF,
+                                    EHScopeStack::LazyCleanup *Fn,
+                                    bool ForEH,
+                                    llvm::BasicBlock *Entry) {
+  assert(Entry && "no entry block for cleanup");
+
+  // Remove the switch and load from the end of the entry block.
+  llvm::Instruction *Switch = &Entry->getInstList().back();
+  Entry->getInstList().remove(Switch);
+  assert(isa<llvm::SwitchInst>(Switch));
+  llvm::Instruction *Load = &Entry->getInstList().back();
+  Entry->getInstList().remove(Load);
+  assert(isa<llvm::LoadInst>(Load));
+
+  assert(Entry->getInstList().empty() &&
+         "lazy cleanup block not empty after removing load/switch pair?");
+
+  // Emit the actual cleanup at the end of the entry block.
+  CGF.Builder.SetInsertPoint(Entry);
+  EmitLazyCleanup(CGF, Fn, ForEH);
+
+  // Put the load and switch at the end of the exit block.
+  llvm::BasicBlock *Exit = CGF.Builder.GetInsertBlock();
+  Exit->getInstList().push_back(Load);
+  Exit->getInstList().push_back(Switch);
+
+  // Clean up the edges if possible.
+  SimplifyCleanupEdges(CGF, Entry, Exit);
+
+  CGF.Builder.ClearInsertionPoint();
+}
+
+static void PopLazyCleanupBlock(CodeGenFunction &CGF) {
+  assert(isa<EHLazyCleanupScope>(*CGF.EHStack.begin()) && "top not a cleanup!");
+  EHLazyCleanupScope &Scope = cast<EHLazyCleanupScope>(*CGF.EHStack.begin());
+  assert(Scope.getFixupDepth() <= CGF.EHStack.getNumBranchFixups());
+
+  // Check whether we need an EH cleanup.  This is only true if we've
+  // generated a lazy EH cleanup block.
+  llvm::BasicBlock *EHEntry = Scope.getEHBlock();
+  bool RequiresEHCleanup = (EHEntry != 0);
+
+  // Check the three conditions which might require a normal cleanup:
+
+  // - whether there are branch fix-ups through this cleanup
+  unsigned FixupDepth = Scope.getFixupDepth();
+  bool HasFixups = CGF.EHStack.getNumBranchFixups() != FixupDepth;
+
+  // - whether control has already been threaded through this cleanup
+  llvm::BasicBlock *NormalEntry = Scope.getNormalBlock();
+  bool HasExistingBranches = (NormalEntry != 0);
+
+  // - whether there's a fallthrough
+  llvm::BasicBlock *FallthroughSource = CGF.Builder.GetInsertBlock();
+  bool HasFallthrough = (FallthroughSource != 0);
+
+  bool RequiresNormalCleanup = false;
+  if (Scope.isNormalCleanup() &&
+      (HasFixups || HasExistingBranches || HasFallthrough)) {
+    RequiresNormalCleanup = true;
+  }
+
+  // If we don't need the cleanup at all, we're done.
+  if (!RequiresNormalCleanup && !RequiresEHCleanup) {
+    CGF.EHStack.popCleanup();
+    assert(CGF.EHStack.getNumBranchFixups() == 0 ||
+           CGF.EHStack.hasNormalCleanups());
+    return;
+  }
+
+  // Copy the cleanup emission data out.  Note that SmallVector
+  // guarantees maximal alignment for its buffer regardless of its
+  // type parameter.
+  llvm::SmallVector<char, 8*sizeof(void*)> CleanupBuffer;
+  CleanupBuffer.reserve(Scope.getCleanupSize());
+  memcpy(CleanupBuffer.data(),
+         Scope.getCleanupBuffer(), Scope.getCleanupSize());
+  CleanupBuffer.set_size(Scope.getCleanupSize());
+  EHScopeStack::LazyCleanup *Fn =
+    reinterpret_cast<EHScopeStack::LazyCleanup*>(CleanupBuffer.data());
+
+  // We're done with the scope; pop it off so we can emit the cleanups.
+  CGF.EHStack.popCleanup();
+
+  if (RequiresNormalCleanup) {
+    // If we have a fallthrough and no other need for the cleanup,
+    // emit it directly.
+    if (HasFallthrough && !HasFixups && !HasExistingBranches) {
+      EmitLazyCleanup(CGF, Fn, /*ForEH*/ false);
+
+    // Otherwise, the best approach is to thread everything through
+    // the cleanup block and then try to clean up after ourselves.
+    } else {
+      // Force the entry block to exist.
+      if (!HasExistingBranches) {
+        NormalEntry = CGF.createBasicBlock("cleanup");
+        CreateCleanupSwitch(CGF, NormalEntry);
+      }
+
+      CGF.EmitBlock(NormalEntry);
+
+      // Thread the fallthrough edge through the (momentarily trivial)
+      // cleanup.
+      llvm::BasicBlock *FallthroughDestination = 0;
+      if (HasFallthrough) {
+        assert(isa<llvm::BranchInst>(FallthroughSource->getTerminator()));
+        FallthroughDestination = CGF.createBasicBlock("cleanup.cont");
+
+        BranchFixup Fix;
+        Fix.Destination = FallthroughDestination;
+        Fix.LatestBranch = FallthroughSource->getTerminator();
+        Fix.LatestBranchIndex = 0;
+        Fix.Origin = Fix.LatestBranch;
+
+        // Restore fixup invariant.  EmitBlock added a branch to the
+        // cleanup which we need to redirect to the destination.
+        cast<llvm::BranchInst>(Fix.LatestBranch)
+          ->setSuccessor(0, Fix.Destination);
+
+        ThreadFixupThroughCleanup(CGF, Fix, NormalEntry, NormalEntry);
+      }
+
+      // Thread any "real" fixups we need to thread.
+      for (unsigned I = FixupDepth, E = CGF.EHStack.getNumBranchFixups();
+           I != E; ++I)
+        if (CGF.EHStack.getBranchFixup(I).Destination)
+          ThreadFixupThroughCleanup(CGF, CGF.EHStack.getBranchFixup(I),
+                                    NormalEntry, NormalEntry);
+
+      SplitAndEmitLazyCleanup(CGF, Fn, /*ForEH*/ false, NormalEntry);
+
+      if (HasFallthrough)
+        CGF.EmitBlock(FallthroughDestination);
+    }
+  }
+
+  // Emit the EH cleanup if required.
+  if (RequiresEHCleanup) {
+    CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveAndClearIP();
+    CGF.EmitBlock(EHEntry);
+    SplitAndEmitLazyCleanup(CGF, Fn, /*ForEH*/ true, EHEntry);
+    CGF.Builder.restoreIP(SavedIP);
+  }
+}
+
 /// Pops a cleanup block.  If the block includes a normal cleanup, the
 /// current insertion point is threaded through the cleanup, as are
 /// any branch fixups on the cleanup.
 void CodeGenFunction::PopCleanupBlock() {
   assert(!EHStack.empty() && "cleanup stack is empty!");
+  if (isa<EHLazyCleanupScope>(*EHStack.begin()))
+    return PopLazyCleanupBlock(*this);
+
   assert(isa<EHCleanupScope>(*EHStack.begin()) && "top not a cleanup!");
   EHCleanupScope &Scope = cast<EHCleanupScope>(*EHStack.begin());
   assert(Scope.getFixupDepth() <= EHStack.getNumBranchFixups());
@@ -1007,6 +1164,16 @@ void CodeGenFunction::EmitBranchThroughCleanup(JumpDest Dest) {
       if (Scope.isNormalCleanup())
         ThreadFixupThroughCleanup(*this, Fixup, Scope.getNormalEntry(),
                                   Scope.getNormalExit());
+    } else if (isa<EHLazyCleanupScope>(*I)) {
+      EHLazyCleanupScope &Scope = cast<EHLazyCleanupScope>(*I);
+      if (Scope.isNormalCleanup()) {
+        llvm::BasicBlock *Block = Scope.getNormalBlock();
+        if (!Block) {
+          Block = createBasicBlock("cleanup");
+          Scope.setNormalBlock(Block);
+        }
+        ThreadFixupThroughCleanup(*this, Fixup, Block, Block);
+      }
     }
   }
   
@@ -1046,6 +1213,16 @@ void CodeGenFunction::EmitBranchThroughEHCleanup(JumpDest Dest) {
       if (Scope.isEHCleanup())
         ThreadFixupThroughCleanup(*this, Fixup, Scope.getEHEntry(),
                                   Scope.getEHExit());
+    } else if (isa<EHLazyCleanupScope>(*I)) {
+      EHLazyCleanupScope &Scope = cast<EHLazyCleanupScope>(*I);
+      if (Scope.isEHCleanup()) {
+        llvm::BasicBlock *Block = Scope.getEHBlock();
+        if (!Block) {
+          Block = createBasicBlock("eh.cleanup");
+          Scope.setEHBlock(Block);
+        }
+        ThreadFixupThroughCleanup(*this, Fixup, Block, Block);
+      }
     }
   }