[analyzer] Teach the analyzer that pointers can escape into __cxa_demangle

[zaks.anna]

Summary

This fixes a reported false positive in the malloc checker.

[NoQ]

LGTM!

This could be probably modeled as realloc, and/or we could look for leaks of its return value, if we wanted.

lib/StaticAnalyzer/Core/CallEvent.cpp

bool AnyFunctionCall::argumentsMayEscape() const {
   //   with xpc_connection_get_context.
   if (II->isStr("xpc_connection_set_context"))
     return true;
 
   // - funopen - sets a buffer for future IO calls.
   if (II->isStr("funopen"))
     return true;
 
+  // - __cxa_demangle - can reallocate memory and can return the pointer to
+  // the input buffer.
+  if (II->isStr("__cxa_demangle"))
+    return true;
+
   StringRef FName = II->getName();
 
   // - CoreFoundation functions that end with "NoCopy" can free a passed-in
   //   buffer even if it is const.
   if (FName.endswith("NoCopy"))
     return true;
 
   // - NSXXInsertXX, for example NSMapInsertIfAbsent, since they can

test/Analysis/Inputs/system-header-simulator-cxx.h

 void* operator new[](std::size_t, const std::nothrow_t&) throw();
 void operator delete(void*, const std::nothrow_t&) throw();
 void operator delete[](void*, const std::nothrow_t&) throw();
 
 void* operator new (std::size_t size, void* ptr) throw() { return ptr; };
 void* operator new[] (std::size_t size, void* ptr) throw() { return ptr; };
 void operator delete (void* ptr, void*) throw() {};
 void operator delete[] (void* ptr, void*) throw() {};
+
+namespace __cxxabiv1 {
+extern "C" {
+extern char *__cxa_demangle(const char *mangled_name,
+                            char *output_buffer,
+                            size_t *length,
+                            int *status);
+}}
+namespace abi = __cxxabiv1;

test/Analysis/malloc.cpp

 // RUN: %clang_cc1 -analyze -analyzer-checker=core,alpha.deadcode.UnreachableCode,alpha.core.CastSize,unix.Malloc -analyzer-store=region -verify %s
 
+#include "Inputs/system-header-simulator-cxx.h"
+
 typedef __typeof(sizeof(int)) size_t;
 void *malloc(size_t);
 void free(void *);
 void *realloc(void *ptr, size_t size);
 void *calloc(size_t nmemb, size_t size);
 char *strdup(const char *s);
 
 void checkThatMallocCheckerIsRunning() {

 void appendNested(NestedProperty x);
 
 void appendWrapperNested(char *getterName) {
   appendNested(NestedProperty(Property(getterName)));
 }
 void fooNested(const char* name) {
   char* getterName = strdup(name);
   appendWrapperNested(getterName); // no-warning
-}
+}
+
+// Allow __cxa_demangle to escape.
+char* test_cxa_demangle(const char* sym) {
+  size_t funcnamesize = 256;
+  char* funcname = (char*)malloc(funcnamesize);
+  int status;
+  char* ret = abi::__cxa_demangle(sym, funcname, &funcnamesize, &status);
+  if (status == 0) {
+    funcname = ret;
+  }
+  return funcname; // no-warning
+}