Restore Check for Unreachable Exit Block in -Winfinite-recursion

[CodaFi]

Summary

When this was rewritten in D43737, the logic changed to better explore infinite loops. The check for a reachable exit block was deleted which accidentally introduced false positives in case the exit node was unreachable.

We were testing for cases like this, but @steven_wu provided an additional test case that I've included in the regression tests for this patch.

[rtrieu]

LGTM

[steven_wu]

LGTM

lib/Sema/AnalysisBasedWarnings.cpp

static void checkRecursiveFunction(Sema &S, const FunctionDecl *FD,
   // templated classes.
   if (FD->getTemplatedKind() != FunctionDecl::TK_NonTemplate &&
       FD->getTemplatedKind() != FunctionDecl::TK_MemberSpecialization)
     return;
 
   CFG *cfg = AC.getCFG();
   if (!cfg) return;
 
+  // If the exit block is unreachable, skip processing the function.
+  if (cfg->getExit().pred_empty())
+    return;
+
   // Emit diagnostic if a recursive function call is detected for all paths.
   if (checkForRecursiveFunctionCall(FD, cfg))
     S.Diag(Body->getBeginLoc(), diag::warn_infinite_recursive_function);
 }
 
 //===----------------------------------------------------------------------===//
 // Check for throw in a non-throwing function.
 //===----------------------------------------------------------------------===//

test/SemaCXX/warn-infinite-recursion.cpp

void i(int x) {  // expected-warning{{call itself}}
   }
   i(0);
 }
 
 int j() {  // expected-warning{{call itself}}
   return 5 + j();
 }
 
-void k() {  // expected-warning{{call itself}}
+// Don't warn on infinite loops
+void k() {
   while(true) {
     k();
   }
 }
 
-// Don't warn on infinite loops
 void l() {
   while (true) {}
 
   l();
 }
 
+void m() {
+  static int count = 5;
+  if (count >0) {
+    count--;
+    l();
+  }
+  while (true) {}
+}
+
 class S {
   static void a();
   void b();
 };
 
 void S::a() {  // expected-warning{{call itself}}
   return a();
 }