Don't warn on fall-through from unreachable code.

Summary:
A motivating example:
class ClassWithDtor {
public:
  ~ClassWithDtor() {}
};
void fallthrough3(int n) {
  switch (n) {
    case 2:
      do {
        ClassWithDtor temp;
        return;
      } while (0);  // This generates a chain of unreachable CFG blocks.
    case 3:
      break;
  }
}

Reviewers: rsmith, doug.gregor, alexfh

Reviewed By: alexfh

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D330

llvm-svn: 173889

1 files changed, 22 insertions, 7 deletions

diff --git a/clang/test/SemaCXX/switch-implicit-fallthrough.cpp b/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
index 93e724e86c6..912b21ebfdb 100644
--- a/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
+++ b/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
@@ -10,7 +10,7 @@ int fallthrough(int n) {
       } else if (n - 3) {
         n = 102;
       }
-    case -1: // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert '[[clang::fallthrough]];' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
+    case -1:  // no warning here, ignore fall-through from unreachable code
       ;
     case 0: {// expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert '[[clang::fallthrough]];' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
     }
@@ -39,14 +39,13 @@ int fallthrough(int n) {
       break;
   }
   switch (n / 15) {
-label_case_70:
-    case 70:
+label_default:
+    default:
       n += 333;
+      if (n % 10)
+        goto label_default;
       break;
-    case 71:
-      n += 334;
-      goto label_case_70;
-    case 72:
+    case 70:
       n += 335;
       break;
   }
@@ -130,6 +129,22 @@ void fallthrough2(int n) {
   }
 }
 
+void fallthrough3(int n) {
+  switch (n) {
+    case 1:
+      do {
+        return;
+      } while (0);
+    case 2:
+      do {
+        ClassWithDtor temp;
+        return;
+      } while (0);
+    case 3:
+      break;
+  }
+}
+
 #define MY_SWITCH(X, Y, Z, U, V) switch (X) { case Y: Z; case U: V; }
 #define MY_SWITCH2(X, Y, Z) switch (X) { Y; Z; }
 #define MY_CASE(X, Y) case X: Y