3 files changed, 52 insertions, 27 deletions

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index 46873bf0621..0b7f3a06a70 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -357,11 +357,15 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
     return RValue::get(Builder.CreateCall(F));
   }
   case Builtin::BI__builtin_unreachable: {
-    if (CatchUndefined && HaveInsertPoint())
+    if (CatchUndefined)
       EmitBranch(getTrapBB());
-    Value *V = Builder.CreateUnreachable();
-    Builder.ClearInsertionPoint();
-    return RValue::get(V);
+    else
+      Builder.CreateUnreachable();
+
+    // We do need to preserve an insertion point.
+    CGF.EmitBlock(createBasicBlock("unreachable.cont"));
+
+    return RValue::get(0);
   }
       
   case Builtin::BI__builtin_powi:
@@ -629,9 +633,12 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
                                   : Intrinsic::eh_return_i64,
                                 0, 0);
     Builder.CreateCall2(F, Int, Ptr);
-    Value *V = Builder.CreateUnreachable();
-    Builder.ClearInsertionPoint();
-    return RValue::get(V);
+    Builder.CreateUnreachable();
+
+    // We do need to preserve an insertion point.
+    CGF.EmitBlock(CGF.createBasicBlock("builtin_eh_return.cont"));
+
+    return RValue::get(0);
   }
   case Builtin::BI__builtin_unwind_init: {
     Value *F = CGM.getIntrinsic(Intrinsic::eh_unwind_init, 0, 0);
@@ -694,10 +701,13 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
     // Call LLVM's EH longjmp, which is lightweight.
     Builder.CreateCall(CGM.getIntrinsic(Intrinsic::eh_sjlj_longjmp), Buf);
 
-    // longjmp doesn't return; mark this as unreachable
-    Value *V = Builder.CreateUnreachable();
-    Builder.ClearInsertionPoint();
-    return RValue::get(V);
+    // longjmp doesn't return; mark this as unreachable.
+    Builder.CreateUnreachable();
+
+    // We do need to preserve an insertion point.
+    CGF.EmitBlock(CGF.createBasicBlock("longjmp.cont"));
+
+    return RValue::get(0);
   }
   case Builtin::BI__sync_fetch_and_add:
   case Builtin::BI__sync_fetch_and_sub:
diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
index 11e5e645280..252e547b5d1 100644
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -577,8 +577,10 @@ void CodeGenFunction::EmitCXXThrowExpr(const CXXThrowExpr *E) {
       Builder.CreateUnreachable();
     }
 
-    // Clear the insertion point to indicate we are in unreachable code.
-    Builder.ClearInsertionPoint();
+    // throw is an expression, and the expression emitters expect us
+    // to leave ourselves at a valid insertion point.
+    EmitBlock(createBasicBlock("throw.cont"));
+
     return;
   }
 
@@ -627,12 +629,9 @@ void CodeGenFunction::EmitCXXThrowExpr(const CXXThrowExpr *E) {
     Builder.CreateUnreachable();
   }
 
-  // Clear the insertion point to indicate we are in unreachable code.
-  Builder.ClearInsertionPoint();
-
-  // FIXME: For now, emit a dummy basic block because expr emitters in generally
-  // are not ready to handle emitting expressions at unreachable points.
-  EnsureInsertPoint();
+  // throw is an expression, and the expression emitters expect us
+  // to leave ourselves at a valid insertion point.
+  EmitBlock(createBasicBlock("throw.cont"));
 }
 
 void CodeGenFunction::EmitStartEHSpec(const Decl *D) {
diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index dbef09f63a8..b0278c7d02d 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -89,18 +89,34 @@ void CodeGenFunction::EmitStmt(const Stmt *S) {
 #define EXPR(Type, Base) \
   case Stmt::Type##Class:
 #include "clang/AST/StmtNodes.inc"
+  {
+    // Remember the block we came in on.
+    llvm::BasicBlock *incoming = Builder.GetInsertBlock();
+    assert(incoming && "expression emission must have an insertion point");
+
     EmitIgnoredExpr(cast<Expr>(S));
 
-    // Expression emitters don't handle unreachable blocks yet, so look for one
-    // explicitly here. This handles the common case of a call to a noreturn
-    // function.
-    if (llvm::BasicBlock *CurBB = Builder.GetInsertBlock()) {
-      if (CurBB->empty() && CurBB->use_empty()) {
-        CurBB->eraseFromParent();
-        Builder.ClearInsertionPoint();
-      }
+    llvm::BasicBlock *outgoing = Builder.GetInsertBlock();
+    assert(outgoing && "expression emission cleared block!");
+
+    // The expression emitters assume (reasonably!) that the insertion
+    // point is always set.  To maintain that, the call-emission code
+    // for noreturn functions has to enter a new block with no
+    // predecessors.  We want to kill that block and mark the current
+    // insertion point unreachable in the common case of a call like
+    // "exit();".  Since expression emission doesn't otherwise create
+    // blocks with no predecessors, we can just test for that.
+    // However, we must be careful not to do this to our incoming
+    // block, because *statement* emission does sometimes create
+    // reachable blocks which will have no predecessors until later in
+    // the function.  This occurs with, e.g., labels that are not
+    // reachable by fallthrough.
+    if (incoming != outgoing && outgoing->use_empty()) {
+      outgoing->eraseFromParent();
+      Builder.ClearInsertionPoint();
     }
     break;
+  }
 
   case Stmt::IndirectGotoStmtClass:
     EmitIndirectGotoStmt(cast<IndirectGotoStmt>(*S)); break;