[clang][analyzer] Enable core.builtin even with -no-default-checks

[zinovy.nis]

Summary

It's required to properly handle attribute(([analyzer_]noreturn)) in checks.

See also https://reviews.llvm.org/D66042

[Szelethus]

This doesn't seem to be in line with the current idea behind core checkers. Turning them off is strongly disencouraged as they are responsible for essential modeling. If you use --analyzer-no-default-checks, i can only imagine that the expected behaviour is to turn them off for good despite the warning.

If we want to create a world where checkers are only responsible for report emission and not modeling (which we are working on!), then we could change the behaviour to turn off all reporting checkers, but not default modeling checkers. This is however pretty much impossible with how intertwined everything is. Yet.

[Szelethus]

@Charusso implemented a flag that can silence checkers in D66042. I can offer that as an alternative while we're working on separating modeling and reporting in the checker insfrastructure.

clang/lib/Driver/ToolChains/Clang.cpp

       CmdArgs.push_back("-analyzer-checker=security.insecureAPI.mktemp");
       CmdArgs.push_back("-analyzer-checker=security.insecureAPI.mkstemp");
       CmdArgs.push_back("-analyzer-checker=security.insecureAPI.vfork");
     }
 
     // Default nullability checks.
     CmdArgs.push_back("-analyzer-checker=nullability.NullPassedToNonnull");
     CmdArgs.push_back("-analyzer-checker=nullability.NullReturnedFromNonnull");
+  } else {
+    // These pseudo-checkers handle assert-like functions and generate no
+    // warnings. They are required to prevent massive false-positive findings.
+    CmdArgs.push_back("-analyzer-checker=core.builtin");
   }
 
   // Set the output format. The default is plist, for (lame) historical reasons.
   CmdArgs.push_back("-analyzer-output");
   if (Arg *A = Args.getLastArg(options::OPT__analyzer_output))
     CmdArgs.push_back(A->getValue());
   else
     CmdArgs.push_back("plist");

clang/test/Analysis/no-default-checks.cpp

+// RUN: %clang -std=c++14 --analyze --analyzer-no-default-checks -Xclang -analyzer-checker=core.CallAndMessage -Xclang -verify %s -o - 
+
+// expected-no-diagnostics
+
+inline constexpr bool AnalyzerNoReturn() __attribute__((analyzer_noreturn)) {
+  return false;
+}
+ 
+struct A {
+   int size();
+};
+
+int foo(A* pa) {
+  if (!pa)
+    AnalyzerNoReturn();
+  // No warning on "Called C++ object pointer is null" is expected 
+  // as |pa| has already been checked for nullptr by this point.
+  return pa->size();
+}
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