commit 36ef0d54cfddf31cd48816e78ab4db73b31a6c1d
author Richard Smith <richard-llvm@metafoo.co.uk> Thu Oct 04 23:52:29 2012 +0000
committer Richard Smith <richard-llvm@metafoo.co.uk> Thu Oct 04 23:52:29 2012 +0000
tree a7b58d06715aadcfe6ff90abdf525f2ab1dfdbef
parent c339393067438596599b142a8950f0e8694e2f1a

If we flow off the end of a value-returning function:
 - outside C++, return undef (behavior is not undefined unless the value is used)
 - in C++, with -fcatch-undefined-behavior, perform an appropriate trap
 - in C++, produce an 'unreachable' (behavior is undefined immediately)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@165273 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CodeGenFunction.cpp

diff --git a/lib/CodeGen/CodeGenFunction.cpp b/lib/CodeGen/CodeGenFunction.cpp
index 1d02861..5c0247a 100644
--- a/lib/CodeGen/CodeGenFunction.cpp
+++ b/lib/CodeGen/CodeGenFunction.cpp
@@ -535,6 +535,20 @@
   else
     EmitFunctionBody(Args);
 
+  // C++11 [stmt.return]p2:
+  //   Flowing off the end of a function [...] results in undefined behavior in
+  //   a value-returning function.
+  // C11 6.9.1p12:
+  //   If the '}' that terminates a function is reached, and the value of the
+  //   function call is used by the caller, the behavior is undefined.
+  if (getContext().getLangOpts().CPlusPlus && !FD->hasImplicitReturnZero() &&
+      !FD->getResultType()->isVoidType() && Builder.GetInsertBlock()) {
+    if (CatchUndefined)
+      EmitCheck(Builder.getFalse());
+    Builder.CreateUnreachable();
+    Builder.ClearInsertionPoint();
+  }
+
   // Emit the standard function epilogue.
   FinishFunction(BodyRange.getEnd());
 

test/CodeGen/catch-undef-behavior.c

diff --git a/test/CodeGen/catch-undef-behavior.c b/test/CodeGen/catch-undef-behavior.c
index 5832b6c..53dda5c 100644
--- a/test/CodeGen/catch-undef-behavior.c
+++ b/test/CodeGen/catch-undef-behavior.c
@@ -44,3 +44,11 @@
   // CHECK-NEXT: ret i32 %[[RET]]
   return a >> b;
 }
+
+// CHECK: @no_return
+int no_return() {
+  // Reaching the end of a noreturn function is fine in C.
+  // CHECK-NOT: call
+  // CHECK-NOT: unreachable
+  // CHECK: ret i32
+}

test/CodeGenCXX/catch-undef-behavior.cpp

diff --git a/test/CodeGenCXX/catch-undef-behavior.cpp b/test/CodeGenCXX/catch-undef-behavior.cpp
index 0ec1cc1..fdc2b00 100644
--- a/test/CodeGenCXX/catch-undef-behavior.cpp
+++ b/test/CodeGenCXX/catch-undef-behavior.cpp
@@ -86,3 +86,9 @@
   // CHECK-NEXT: ret i32 %[[RET]]
   return a << b;
 }
+
+// CHECK: @_Z9no_return
+int no_return() {
+  // CHECK: call void @llvm.trap
+  // CHECK: unreachable
+}

test/CodeGenCXX/return.cpp

diff --git a/test/CodeGenCXX/return.cpp b/test/CodeGenCXX/return.cpp
new file mode 100644
index 0000000..2af1a52
--- /dev/null
+++ b/test/CodeGenCXX/return.cpp
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck %s
+
+// CHECK: @_Z9no_return
+int no_return() {
+  // CHECK: unreachable
+}