Index: include/clang/StaticAnalyzer/Checkers/Checkers.td
===================================================================
--- include/clang/StaticAnalyzer/Checkers/Checkers.td
+++ include/clang/StaticAnalyzer/Checkers/Checkers.td
@@ -99,6 +99,10 @@
   HelpText<"Check for dereferences of null pointers">,
   DescFile<"DereferenceChecker.cpp">;
 
+def ModelBuiltinsChecker : Checker<"ModelBuiltins">,
+  HelpText<"Model some compiler builtin functions">,
+  DescFile<"ModelBuiltinChecker.cpp">;
+
 def CallAndMessageChecker : Checker<"CallAndMessage">,
   HelpText<"Check for logical errors for function calls and Objective-C message expressions (e.g., uninitialized arguments, null function pointers)">,
   DescFile<"CallAndMessageChecker.cpp">;
Index: lib/StaticAnalyzer/Checkers/CMakeLists.txt
===================================================================
--- lib/StaticAnalyzer/Checkers/CMakeLists.txt
+++ lib/StaticAnalyzer/Checkers/CMakeLists.txt
@@ -49,6 +49,7 @@
   MallocOverflowSecurityChecker.cpp
   MallocSizeofChecker.cpp
   MisusedMovedObjectChecker.cpp
+  ModelBuiltinChecker.cpp
   MPI-Checker/MPIBugReporter.cpp
   MPI-Checker/MPIChecker.cpp
   MPI-Checker/MPIFunctionClassifier.cpp
Index: lib/StaticAnalyzer/Checkers/ModelBuiltinChecker.cpp
===================================================================
--- /dev/null
+++ lib/StaticAnalyzer/Checkers/ModelBuiltinChecker.cpp
@@ -0,0 +1,59 @@
+//=== ModelBuiltinChecker.cpp --------- Model builtin functions -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This checker improves modeling of a few builtin compiler functions.
+// It does not generate warnings.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+
+using namespace clang;
+using namespace clang::ento;
+
+namespace {
+class ModelBuiltinsChecker : public Checker<eval::Call> {
+public:
+  bool evalCall(const CallExpr *CE, CheckerContext &C) const {
+    const FunctionDecl *FD =
+        dyn_cast_or_null<FunctionDecl>(CE->getCalleeDecl());
+    if (!FD)
+      return false;
+    if (!FD->getIdentifier())
+      return false;
+
+    StringRef Name = FD->getName();
+    if (Name.empty() || !C.isCLibraryFunction(FD, Name) ||
+        Name != "__builtin_assume")
+      return false;
+
+    ProgramStateRef State = C.getState();
+    const LocationContext *LC = C.getLocationContext();
+    SVal ArgSVal = State->getSVal(CE->getArg(0), LC);
+    if (ArgSVal.isUndef())
+      return false;
+
+    State = State->assume(ArgSVal.castAs<DefinedOrUnknownSVal>(), true);
+    // FIXME: do we want to warn here?
+    if (!State)
+      return false;
+
+    C.addTransition(State);
+    return true;
+  }
+};
+} // end of anonymous namespace
+
+void ento::registerModelBuiltinsChecker(CheckerManager &mgr) {
+  mgr.registerChecker<ModelBuiltinsChecker>();
+}
Index: test/Analysis/builtin-assume.c
===================================================================
--- /dev/null
+++ test/Analysis/builtin-assume.c
@@ -0,0 +1,8 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=core,debug.ExprInspection -verify %s
+
+void clang_analyzer_eval(int);
+
+void f(int i) {
+  __builtin_assume(i < 10);
+  clang_analyzer_eval(i < 15); // expected-warning {{TRUE}}
+}