Analysis: Add a CFG successor to a SwitchStmt if it is both empty and fully covered

Consider the case where a SwitchStmt satisfied isAllEnumCasesCovered()
as well as having no cases at all (i.e. the enum it covers has no
enumerators).

In this case, we should add a successor to repair the CFG.

This fixes PR16212.

llvm-svn: 183237

Author: majnemer

clang/lib/Analysis/CFG.cpp

@@ -2671,9 +2671,15 @@ CFGBlock *CFGBuilder::VisitSwitchStmt(SwitchStmt *Terminator) {
   // If we have no "default:" case, the default transition is to the code
   // following the switch body.  Moreover, take into account if all the
   // cases of a switch are covered (e.g., switching on an enum value).
+  //
+  // Note: We add a successor to a switch that is considered covered yet has no
+  //       case statements if the enumeration has no enumerators.
+  bool SwitchAlwaysHasSuccessor = false;
+  SwitchAlwaysHasSuccessor |= switchExclusivelyCovered;
+  SwitchAlwaysHasSuccessor |= Terminator->isAllEnumCasesCovered() &&
+                              Terminator->getSwitchCaseList();
   addSuccessor(SwitchTerminatedBlock,
-               switchExclusivelyCovered || Terminator->isAllEnumCasesCovered()
-               ? 0 : DefaultCaseBlock);
+               SwitchAlwaysHasSuccessor ? 0 : DefaultCaseBlock);
 
   // Add the terminator and condition in the switch block.
   SwitchTerminatedBlock->setTerminator(Terminator);

clang/test/Analysis/cfg.cpp

@@ -66,3 +66,19 @@ void checkDeclStmts() {
 
   static_assert(1, "abc");
 }
+
+// CHECK: ENTRY
+// CHECK-NEXT: Succs (1): B1
+// CHECK: [B1]
+// CHECK-NEXT:   1: e
+// CHECK-NEXT:   2: [B1.1] (ImplicitCastExpr, LValueToRValue, enum EmptyE)
+// CHECK-NEXT:   3: [B1.2] (ImplicitCastExpr, IntegralCast, int)
+// CHECK-NEXT:   T: switch [B1.3]
+// CHECK-NEXT:   Preds (1): B2
+// CHECK-NEXT:   Succs (1): B0
+// CHECK: [B0 (EXIT)]
+// CHECK-NEXT:   Preds (1): B1
+enum EmptyE {};
+void F(EmptyE e) {
+  switch (e) {}
+}