[analyzer] do not warn about returning stack-allocated memory when it comes from an ancestor stack frame.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151964 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/StaticAnalyzer/Checkers/StackAddrEscapeChecker.cpp b/lib/StaticAnalyzer/Checkers/StackAddrEscapeChecker.cpp
index d071ef8..8c76cc5 100644
--- a/lib/StaticAnalyzer/Checkers/StackAddrEscapeChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/StackAddrEscapeChecker.cpp
@@ -113,7 +113,7 @@
 }
 
 void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
-                                        CheckerContext &C) const {
+                                          CheckerContext &C) const {
   
   const Expr *RetE = RS->getRetValue();
   if (!RetE)
@@ -122,18 +122,26 @@
   SVal V = C.getState()->getSVal(RetE, C.getLocationContext());
   const MemRegion *R = V.getAsRegion();
 
-  if (!R || !R->hasStackStorage())
-    return;  
-  
-  if (R->hasStackStorage()) {
-    // Automatic reference counting automatically copies blocks.
-    if (C.getASTContext().getLangOptions().ObjCAutoRefCount &&
-        isa<BlockDataRegion>(R))
-      return;
-
-    EmitStackError(C, R, RetE);
+  if (!R)
     return;
-  }
+  
+  const StackSpaceRegion *SS =
+    dyn_cast_or_null<StackSpaceRegion>(R->getMemorySpace());
+    
+  if (!SS)
+    return;
+
+  // Return stack memory in an ancestor stack frame is fine.
+  const StackFrameContext *SFC = SS->getStackFrame();
+  if (SFC != C.getLocationContext()->getCurrentStackFrame())
+    return;
+
+  // Automatic reference counting automatically copies blocks.
+  if (C.getASTContext().getLangOptions().ObjCAutoRefCount &&
+      isa<BlockDataRegion>(R))
+    return;
+
+  EmitStackError(C, R, RetE);
 }
 
 void StackAddrEscapeChecker::checkEndPath(CheckerContext &Ctx) const {
diff --git a/test/Analysis/inline.c b/test/Analysis/inline.c
index de807fb..9e64d33 100644
--- a/test/Analysis/inline.c
+++ b/test/Analysis/inline.c
@@ -58,3 +58,22 @@
     *p = 0xDEADBEEF; // no-warning
   }
 }
+
+// Test that returning stack memory from a parent stack frame does
+// not trigger a warning.
+static char *return_buf(char *buf) {
+  return buf + 10;
+}
+
+void test_return_stack_memory_ok() {
+  char stack_buf[100];
+  char *pos = return_buf(stack_buf);
+  (void) pos;
+}
+
+char *test_return_stack_memory_bad() {
+  char stack_buf[100];
+  char *x = stack_buf;
+  return x; // expected-warning {{stack memory associated}}
+}
+