Omit arguments of __builtin_object_size from the CFG.

This builtin does not actually evaluate its arguments for side effects,
so we shouldn't include them in the CFG. In the analyzer, rely on the
constant expression evaluator to get the proper semantics, at least for
now. (In the future, we could get ambitious and try to provide path-
sensitive size values.)

In theory, this does pose a problem for liveness analysis: a variable can
be used within the __builtin_object_size argument expression but not show
up as live. However, it is very unlikely that such a value would be used
to compute the object size and not used to access the object in some way.

<rdar://problem/14760817>

llvm-svn: 188679

1 files changed, 19 insertions, 6 deletions

diff --git a/clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
index 5300fae7756..a8710498488 100644
--- a/clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
@@ -37,12 +37,10 @@ bool BuiltinFunctionChecker::evalCall(const CallExpr *CE,
   if (!FD)
     return false;
 
-  unsigned id = FD->getBuiltinID();
-
-  if (!id)
+  switch (FD->getBuiltinID()) {
+  default:
     return false;
 
-  switch (id) {
   case Builtin::BI__builtin_expect:
   case Builtin::BI__builtin_addressof: {
     // For __builtin_expect, just return the value of the subexpression.
@@ -76,9 +74,24 @@ bool BuiltinFunctionChecker::evalCall(const CallExpr *CE,
     C.addTransition(state->BindExpr(CE, LCtx, loc::MemRegionVal(R)));
     return true;
   }
-  }
 
-  return false;
+  case Builtin::BI__builtin_object_size: {
+    // This must be resolvable at compile time, so we defer to the constant
+    // evaluator for a value.
+    SVal V = UnknownVal();
+    llvm::APSInt Result;
+    if (CE->EvaluateAsInt(Result, C.getASTContext(), Expr::SE_NoSideEffects)) {
+      // Make sure the result has the correct type.
+      SValBuilder &SVB = C.getSValBuilder();
+      BasicValueFactory &BVF = SVB.getBasicValueFactory();
+      BVF.getAPSIntType(CE->getType()).apply(Result);
+      V = SVB.makeIntVal(Result);
+    }
+
+    C.addTransition(state->BindExpr(CE, LCtx, V));
+    return true;
+  }
+  }
 }
 
 void ento::registerBuiltinFunctionChecker(CheckerManager &mgr) {