if basic blocks are destroyed while there are *just* BlockAddress' hanging

around, then zap them.  This is analogous to dangling constantexprs hanging
off functions.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85627 91177308-0d34-0410-b5e6-96231b3b80d8

lib/VMCore/BasicBlock.cpp

@@ -58,6 +58,24 @@ BasicBlock::BasicBlock(LLVMContext &C, const Twine &Name, Function *NewParent,
 
 
 BasicBlock::~BasicBlock() {
+  // If the address of the block is taken and it is being deleted (e.g. because
+  // it is dead), this means that there is either a dangling constant expr
+  // hanging off the block, or an undefined use of the block (source code
+  // expecting the address of a label to keep the block alive even though there
+  // is no indirect branch).  Handle these cases by zapping the BlockAddress
+  // nodes.  There are no other possible uses at this point.
+  if (hasAddressTaken()) {
+    assert(!use_empty() && "There should be at least one blockaddress!");
+    Constant *Replacement =
+      ConstantInt::get(llvm::Type::getInt32Ty(getContext()), 1);
+    while (!use_empty()) {
+      BlockAddress *BA = cast<BlockAddress>(use_back());
+      BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
+                                                       BA->getType()));
+      BA->destroyConstant();
+    }
+  }
+  
   assert(getParent() == 0 && "BasicBlock still linked into the program!");
   dropAllReferences();
   InstList.clear();

test/Transforms/SimplifyCFG/basictest.ll

@@ -21,5 +21,10 @@ BB1:            ; preds = %0, %0
 }
 
 
-
+define void @test4() {
-
+entry:
+ br label %return
+return:
+ ret void
+}
+@test4g = global i8* blockaddress(@test4, %return)