Index: compiler-rt/trunk/lib/ubsan/ubsan_checks.inc
===================================================================
--- compiler-rt/trunk/lib/ubsan/ubsan_checks.inc
+++ compiler-rt/trunk/lib/ubsan/ubsan_checks.inc
@@ -29,6 +29,7 @@
 UBSAN_CHECK(IntegerDivideByZero, "integer-divide-by-zero",
             "integer-divide-by-zero")
 UBSAN_CHECK(FloatDivideByZero, "float-divide-by-zero", "float-divide-by-zero")
+UBSAN_CHECK(InvalidBuiltin, "invalid-builtin-use", "invalid-builtin-use")
 UBSAN_CHECK(InvalidShiftBase, "invalid-shift-base", "shift-base")
 UBSAN_CHECK(InvalidShiftExponent, "invalid-shift-exponent", "shift-exponent")
 UBSAN_CHECK(OutOfBoundsIndex, "out-of-bounds-index", "bounds")
Index: compiler-rt/trunk/lib/ubsan/ubsan_handlers.h
===================================================================
--- compiler-rt/trunk/lib/ubsan/ubsan_handlers.h
+++ compiler-rt/trunk/lib/ubsan/ubsan_handlers.h
@@ -122,6 +122,21 @@
 /// \brief Handle a load of an invalid value for the type.
 RECOVERABLE(load_invalid_value, InvalidValueData *Data, ValueHandle Val)
 
+/// Known builtin check kinds.
+/// Keep in sync with the enum of the same name in CodeGenFunction.h
+enum BuiltinCheckKind : unsigned char {
+  BCK_CTZPassedZero,
+  BCK_CLZPassedZero,
+};
+
+struct InvalidBuiltinData {
+  SourceLocation Loc;
+  unsigned char Kind;
+};
+
+/// Handle a builtin called in an invalid way.
+RECOVERABLE(invalid_builtin, InvalidBuiltinData *Data)
+
 struct FunctionTypeMismatchData {
   SourceLocation Loc;
   const TypeDescriptor &Type;
Index: compiler-rt/trunk/lib/ubsan/ubsan_handlers.cc
===================================================================
--- compiler-rt/trunk/lib/ubsan/ubsan_handlers.cc
+++ compiler-rt/trunk/lib/ubsan/ubsan_handlers.cc
@@ -437,6 +437,30 @@
   Die();
 }
 
+static void handleInvalidBuiltin(InvalidBuiltinData *Data, ReportOptions Opts) {
+  SourceLocation Loc = Data->Loc.acquire();
+  ErrorType ET = ErrorType::InvalidBuiltin;
+
+  if (ignoreReport(Loc, Opts, ET))
+    return;
+
+  ScopedReport R(Opts, Loc, ET);
+
+  Diag(Loc, DL_Error,
+       "passing zero to %0, which is not a valid argument")
+    << ((Data->Kind == BCK_CTZPassedZero) ? "ctz()" : "clz()");
+}
+
+void __ubsan::__ubsan_handle_invalid_builtin(InvalidBuiltinData *Data) {
+  GET_REPORT_OPTIONS(true);
+  handleInvalidBuiltin(Data, Opts);
+}
+void __ubsan::__ubsan_handle_invalid_builtin_abort(InvalidBuiltinData *Data) {
+  GET_REPORT_OPTIONS(true);
+  handleInvalidBuiltin(Data, Opts);
+  Die();
+}
+
 static void handleFunctionTypeMismatch(FunctionTypeMismatchData *Data,
                                        ValueHandle Function,
                                        ReportOptions Opts) {
Index: compiler-rt/trunk/lib/ubsan/ubsan_interface.inc
===================================================================
--- compiler-rt/trunk/lib/ubsan/ubsan_interface.inc
+++ compiler-rt/trunk/lib/ubsan/ubsan_interface.inc
@@ -19,6 +19,8 @@
 INTERFACE_FUNCTION(__ubsan_handle_float_cast_overflow_abort)
 INTERFACE_FUNCTION(__ubsan_handle_function_type_mismatch)
 INTERFACE_FUNCTION(__ubsan_handle_function_type_mismatch_abort)
+INTERFACE_FUNCTION(__ubsan_handle_invalid_builtin)
+INTERFACE_FUNCTION(__ubsan_handle_invalid_builtin_abort)
 INTERFACE_FUNCTION(__ubsan_handle_load_invalid_value)
 INTERFACE_FUNCTION(__ubsan_handle_load_invalid_value_abort)
 INTERFACE_FUNCTION(__ubsan_handle_missing_return)
Index: compiler-rt/trunk/test/ubsan/TestCases/Misc/builtins.cpp
===================================================================
--- compiler-rt/trunk/test/ubsan/TestCases/Misc/builtins.cpp
+++ compiler-rt/trunk/test/ubsan/TestCases/Misc/builtins.cpp
@@ -0,0 +1,35 @@
+// REQUIRES: arch=x86_64
+//
+// RUN: %clangxx -fsanitize=builtin -w %s -O3 -o %t
+// RUN: %run %t 2>&1 | FileCheck %s --check-prefix=RECOVER
+// RUN: %clangxx -fsanitize=builtin -fno-sanitize-recover=builtin -w %s -O3 -o %t.abort
+// RUN: not %run %t.abort 2>&1 | FileCheck %s --check-prefix=ABORT
+
+void check_ctz(int n) {
+  // ABORT: builtins.cpp:[[@LINE+2]]:17: runtime error: passing zero to ctz(), which is not a valid argument
+  // RECOVER: builtins.cpp:[[@LINE+1]]:17: runtime error: passing zero to ctz(), which is not a valid argument
+  __builtin_ctz(n);
+
+  // RECOVER: builtins.cpp:[[@LINE+1]]:18: runtime error: passing zero to ctz(), which is not a valid argument
+  __builtin_ctzl(n);
+
+  // RECOVER: builtins.cpp:[[@LINE+1]]:19: runtime error: passing zero to ctz(), which is not a valid argument
+  __builtin_ctzll(n);
+}
+
+void check_clz(int n) {
+  // RECOVER: builtins.cpp:[[@LINE+1]]:17: runtime error: passing zero to clz(), which is not a valid argument
+  __builtin_clz(n);
+
+  // RECOVER: builtins.cpp:[[@LINE+1]]:18: runtime error: passing zero to clz(), which is not a valid argument
+  __builtin_clzl(n);
+
+  // RECOVER: builtins.cpp:[[@LINE+1]]:19: runtime error: passing zero to clz(), which is not a valid argument
+  __builtin_clzll(n);
+}
+
+int main() {
+  check_ctz(0);
+  check_clz(0);
+  return 0;
+}
Index: compiler-rt/trunk/test/ubsan/lit.common.cfg
===================================================================
--- compiler-rt/trunk/test/ubsan/lit.common.cfg
+++ compiler-rt/trunk/test/ubsan/lit.common.cfg
@@ -77,3 +77,5 @@
 # because the test hangs or fails on one configuration and not the other.
 if config.target_arch.startswith('arm') == False and config.target_arch != 'aarch64':
   config.available_features.add('stable-runtime')
+
+config.available_features.add('arch=' + config.target_arch)