[analyzer] Fix GCDAntipatternChecker to only fire when the semaphore is initialized to zero

[george.karpenkov]

Summary

Initializing a semaphore with a different constant most likely signals a different intent

rdar://41802552

[NoQ]

lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp

96–99

I suspect that allOf can be omitted here.

lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp

if (const auto *OD = dyn_cast<ObjCMethodDecl>(D)) {
     }
   }
   return false;
 }
 
 static auto findGCDAntiPatternWithSemaphore() -> decltype(compoundStmt()) {
 
   const char *SemaphoreBinding = "semaphore_name";
-  auto SemaphoreCreateM = callExpr(callsName("dispatch_semaphore_create"));
+  auto SemaphoreCreateM = callExpr(allOf(
+      callsName("dispatch_semaphore_create"),
+      hasArgument(0, ignoringParenCasts(integerLiteral(equals(0))))));
 
   auto SemaphoreBindingM = anyOf(
       forEachDescendant(
           varDecl(hasDescendant(SemaphoreCreateM)).bind(SemaphoreBinding)),
       forEachDescendant(binaryOperator(bindAssignmentToDecl(SemaphoreBinding),
                      hasRHS(SemaphoreCreateM))));
 
   auto HasBlockArgumentM = hasAnyArgument(hasType(
             hasCanonicalType(blockPointerType())

test/Analysis/gcdantipatternchecker_test.m

void dispatch_group_and_semaphore_use(MyInterface1 *M) {
 
   dispatch_semaphore_t sema1 = dispatch_semaphore_create(0);
 
   [M acceptBlock:^{
       dispatch_semaphore_signal(sema1);
   }];
   dispatch_semaphore_wait(sema1, 100); // expected-warning{{Waiting on a callback using a semaphore}}
 }
+
+void no_warn_on_nonzero_semaphore(MyInterface1 *M) {
+  dispatch_semaphore_t sema1 = dispatch_semaphore_create(1);
+
+  [M acceptBlock:^{
+      dispatch_semaphore_signal(sema1);
+  }];
+  dispatch_semaphore_wait(sema1, 100); // no-warning
+}
+