[CodeGen] Point empty %invoke.cont block to successor

[vsk]

Summary

When partially initializing a global, exception-handling code in the frontend emits a placeholder %invoke.cont block with no terminator. This commit adds a suitable BranchInst to the block to prevent "malformed BasicBlock" errors.

A test case is included.

Note: I have been struggling to understand why throwing an error in a destructor causes exception-handling code to be generated when invoking the constructor [esp. when the constructor does not throw anything]. This patch is meant as a workaround until the 'real' issue can be addressed.

[vsk]

Ping

[rnk]

I think a better fix would be to insert a non-terminator placeholder that doesn't confuse EmitBlock.

lib/CodeGen/CGExprAgg.cpp

if (NumInitElements != NumArrayElements &&
     // Compute the end of the array.
     llvm::Value *end = Builder.CreateInBoundsGEP(begin,
                       llvm::ConstantInt::get(CGF.SizeTy, NumArrayElements),
                                                  "arrayinit.end");
 
     llvm::BasicBlock *entryBB = Builder.GetInsertBlock();
     llvm::BasicBlock *bodyBB = CGF.createBasicBlock("arrayinit.body");
 
+    // The exception-handling code in VisitInitListExpr may mark entryBB as
+    // a placeholder with an UnreachableInst. Branch to bodyBB as intended.
+    if (dyn_cast_or_null<llvm::UnreachableInst>(entryBB->getTerminator())) {
+      llvm::BranchInst::Create(bodyBB, entryBB);
+    }
+
     // Jump into the body.
     CGF.EmitBlock(bodyBB);
     llvm::PHINode *currentElement =
       Builder.CreatePHI(element->getType(), 2, "arrayinit.cur");
     currentElement->addIncoming(element, entryBB);
 
     // Emit the actual filler expression.
     LValue elementLV = CGF.MakeAddrLValue(currentElement, elementType);

test/CodeGenCXX/partial-init.cpp

+// RUN: %clang_cc1 -triple=x86_64-apple-darwin10 -emit-obj -std=c++11 -x c++ \
+// RUN: -fcxx-exceptions -fexceptions -S -emit-llvm -o - %s | FileCheck %s
+
+namespace std {
+  struct string {
+    const char *p;
+    string(const char *s) : p(s) {}
+    ~string() { throw 0; }
+  };
+}
+
+struct Bar {
+  int a;
+};
+
+struct Foo {
+  int b;
+  std::string c;
+  Bar d[32];
+};
+
+static Foo table[] = {
+  { 0, "blerg" },
+};
+
+// CHECK-NOT: does not have terminator
+// CHECK-NOT: Broken function found, compilation aborted