Add support for artificial tail call frames

This patch teaches lldb to detect when there are missing frames in a
backtrace due to a sequence of tail calls, and to fill in the backtrace
with artificial tail call frames when this happens. This is only done
when the execution history can be determined from the call graph and
from the return PC addresses of calls on the stack. Ambiguous sequences
of tail calls (e.g anything involving tail calls and recursion) are
detected and ignored.

Depends on D49887.

Differential Revision: https://reviews.llvm.org/D50478

llvm-svn: 343900

31 files changed, 591 insertions, 0 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/decorators.py b/lldb/packages/Python/lldbsuite/test/decorators.py
index 8b33cad3d1b..59cd3191828 100644
--- a/lldb/packages/Python/lldbsuite/test/decorators.py
+++ b/lldb/packages/Python/lldbsuite/test/decorators.py
@@ -687,6 +687,30 @@ def skipUnlessSupportedTypeAttribute(attr):
         return None
     return skipTestIfFn(compiler_doesnt_support_struct_attribute)
 
+def skipUnlessHasCallSiteInfo(func):
+    """Decorate the function to skip testing unless call site info from clang is available."""
+
+    def is_compiler_clang_with_call_site_info(self):
+        compiler_path = self.getCompiler()
+        compiler = os.path.basename(compiler_path)
+        if not compiler.startswith("clang"):
+            return "Test requires clang as compiler"
+
+        f = tempfile.NamedTemporaryFile()
+        cmd = "echo 'int main() {}' | " \
+              "%s -g -glldb -O1 -S -emit-llvm -x c -o %s -" % (compiler_path, f.name)
+        if os.popen(cmd).close() is not None:
+            return "Compiler can't compile with call site info enabled"
+
+        with open(f.name, 'r') as ir_output_file:
+            buf = ir_output_file.read()
+
+        if 'DIFlagAllCallsDescribed' not in buf:
+            return "Compiler did not introduce DIFlagAllCallsDescribed IR flag"
+
+        return None
+    return skipTestIfFn(is_compiler_clang_with_call_site_info)(func)
+
 def skipUnlessThreadSanitizer(func):
     """Decorate the item to skip test unless Clang -fsanitize=thread is supported."""
 
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq1/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq1/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq1/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq1/TestAmbiguousTailCallSeq1.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq1/TestAmbiguousTailCallSeq1.py
new file mode 100644
index 00000000000..aec4d503fd7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq1/TestAmbiguousTailCallSeq1.py
@@ -0,0 +1,5 @@
+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals(),
+        [decorators.skipUnlessHasCallSiteInfo])
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq1/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq1/main.cpp
new file mode 100644
index 00000000000..48190184be1
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq1/main.cpp
@@ -0,0 +1,33 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) sink() {
+  x++; //% self.filecheck("bt", "main.cpp")
+  // CHECK-NOT: func{{[23]}}_amb
+}
+
+void __attribute__((noinline)) func3_amb() { sink(); /* tail */ }
+
+void __attribute__((noinline)) func2_amb() { sink(); /* tail */ }
+
+void __attribute__((noinline)) func1() {
+  if (x > 0)
+    func2_amb(); /* tail */
+  else
+    func3_amb(); /* tail */
+}
+
+int __attribute__((disable_tail_calls)) main(int argc, char **) {
+  // The sequences `main -> func1 -> f{2,3}_amb -> sink` are both plausible. Test
+  // that lldb doesn't attempt to guess which one occurred.
+  func1();
+  return 0;
+}
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq2/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq2/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq2/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq2/TestAmbiguousTailCallSeq2.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq2/TestAmbiguousTailCallSeq2.py
new file mode 100644
index 00000000000..aec4d503fd7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq2/TestAmbiguousTailCallSeq2.py
@@ -0,0 +1,5 @@
+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals(),
+        [decorators.skipUnlessHasCallSiteInfo])
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq2/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq2/main.cpp
new file mode 100644
index 00000000000..1651db2ea4a
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/ambiguous_tail_call_seq2/main.cpp
@@ -0,0 +1,38 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) sink() {
+  x++; //% self.filecheck("bt", "main.cpp")
+  // CHECK-NOT: func{{[23]}}
+}
+
+void func2();
+
+void __attribute__((noinline)) func1() {
+  if (x < 1)
+    func2();
+  else
+    sink();
+}
+
+void __attribute__((noinline)) func2() {
+  if (x < 1)
+    sink();
+  else
+    func1();
+}
+
+int main() {
+  // Tail recursion creates ambiguous execution histories.
+  x = 0;
+  func1();
+  return 0;
+}
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_call_site/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_call_site/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_call_site/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_call_site/TestDisambiguateCallSite.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_call_site/TestDisambiguateCallSite.py
new file mode 100644
index 00000000000..aec4d503fd7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_call_site/TestDisambiguateCallSite.py
@@ -0,0 +1,5 @@
+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals(),
+        [decorators.skipUnlessHasCallSiteInfo])
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_call_site/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_call_site/main.cpp
new file mode 100644
index 00000000000..d3aef19f7a4
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_call_site/main.cpp
@@ -0,0 +1,32 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) sink() {
+  x++; //% self.filecheck("bt", "main.cpp", "-implicit-check-not=artificial")
+  // CHECK: frame #0: 0x{{[0-9a-f]+}} a.out`sink() at main.cpp:[[@LINE-1]]:4 [opt]
+  // CHECK-NEXT: func2{{.*}} [opt] [artificial]
+  // CHECK-NEXT: main{{.*}} [opt]
+}
+
+void __attribute__((noinline)) func2() {
+  sink(); /* tail */
+}
+
+void __attribute__((noinline)) func1() { sink(); /* tail */ }
+
+int __attribute__((disable_tail_calls)) main(int argc, char **) {
+  // The sequences `main -> f{1,2} -> sink` are both plausible. Test that
+  // return-pc call site info allows lldb to pick the correct sequence.
+  func2();
+  if (argc == 100)
+    func1();
+  return 0;
+}
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_paths_to_common_sink/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_paths_to_common_sink/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_paths_to_common_sink/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_paths_to_common_sink/TestDisambiguatePathsToCommonSink.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_paths_to_common_sink/TestDisambiguatePathsToCommonSink.py
new file mode 100644
index 00000000000..aec4d503fd7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_paths_to_common_sink/TestDisambiguatePathsToCommonSink.py
@@ -0,0 +1,5 @@
+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals(),
+        [decorators.skipUnlessHasCallSiteInfo])
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_paths_to_common_sink/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_paths_to_common_sink/main.cpp
new file mode 100644
index 00000000000..5189218c4ef
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_paths_to_common_sink/main.cpp
@@ -0,0 +1,38 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) sink2() {
+  x++; //% self.filecheck("bt", "main.cpp", "-check-prefix=FROM-FUNC1")
+  // FROM-FUNC1: frame #0: 0x{{[0-9a-f]+}} a.out`sink{{.*}} at main.cpp:[[@LINE-1]]:{{.*}} [opt]
+  // FROM-FUNC1-NEXT: sink({{.*}} [opt]
+  // FROM-FUNC1-NEXT: func1{{.*}} [opt] [artificial]
+  // FROM-FUNC1-NEXT: main{{.*}} [opt]
+}
+
+void __attribute__((noinline)) sink(bool called_from_main) {
+  if (called_from_main) {
+    x++; //% self.filecheck("bt", "main.cpp", "-check-prefix=FROM-MAIN")
+    // FROM-MAIN: frame #0: 0x{{[0-9a-f]+}} a.out`sink{{.*}} at main.cpp:[[@LINE-1]]:{{.*}} [opt]
+    // FROM-MAIN-NEXT: main{{.*}} [opt]
+  } else {
+    sink2();
+  }
+}
+
+void __attribute__((noinline)) func1() { sink(false); /* tail */ }
+
+int __attribute__((disable_tail_calls)) main(int argc, char **) {
+  // When func1 tail-calls sink, make sure that the former appears in the
+  // backtrace.
+  sink(true);
+  func1();
+  return 0;
+}
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_tail_call_seq/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_tail_call_seq/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_tail_call_seq/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_tail_call_seq/TestDisambiguateTailCallSeq.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_tail_call_seq/TestDisambiguateTailCallSeq.py
new file mode 100644
index 00000000000..aec4d503fd7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_tail_call_seq/TestDisambiguateTailCallSeq.py
@@ -0,0 +1,5 @@
+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals(),
+        [decorators.skipUnlessHasCallSiteInfo])
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_tail_call_seq/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_tail_call_seq/main.cpp
new file mode 100644
index 00000000000..3c723b8a3ee
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/disambiguate_tail_call_seq/main.cpp
@@ -0,0 +1,31 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) sink() {
+  x++; //% self.filecheck("bt", "main.cpp", "-implicit-check-not=artificial")
+  // CHECK: frame #0: 0x{{[0-9a-f]+}} a.out`sink() at main.cpp:[[@LINE-1]]:4 [opt]
+  // CHECK-NEXT: func3{{.*}} [opt] [artificial]
+  // CHECK-NEXT: func1{{.*}} [opt] [artificial]
+  // CHECK-NEXT: main{{.*}} [opt]
+}
+
+void __attribute__((noinline)) func3() { sink(); /* tail */ }
+
+void __attribute__((noinline)) func2() { sink(); /* tail */ }
+
+void __attribute__((noinline)) func1() { func3(); /* tail */ }
+
+int __attribute__((disable_tail_calls)) main(int argc, char **) {
+  // The sequences `main -> func1 -> f{2,3} -> sink` are both plausible. Test
+  // that lldb picks the latter sequence.
+  func1();
+  return 0;
+}
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/inlining_and_tail_calls/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/inlining_and_tail_calls/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/inlining_and_tail_calls/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/inlining_and_tail_calls/TestInliningAndTailCalls.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/inlining_and_tail_calls/TestInliningAndTailCalls.py
new file mode 100644
index 00000000000..aec4d503fd7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/inlining_and_tail_calls/TestInliningAndTailCalls.py
@@ -0,0 +1,5 @@
+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals(),
+        [decorators.skipUnlessHasCallSiteInfo])
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/inlining_and_tail_calls/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/inlining_and_tail_calls/main.cpp
new file mode 100644
index 00000000000..e4504ad151f
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/inlining_and_tail_calls/main.cpp
@@ -0,0 +1,50 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) tail_call_sink() {
+  x++; //% self.filecheck("bt", "main.cpp", "-check-prefix=TAIL-CALL-SINK")
+  // TAIL-CALL-SINK: frame #0: 0x{{[0-9a-f]+}} a.out`tail_call_sink() at main.cpp:[[@LINE-1]]:4 [opt]
+  // TAIL-CALL-SINK-NEXT: func3{{.*}} [opt] [artificial]
+  // TAIL-CALL-SINK-NEXT: main{{.*}} [opt]
+
+  // TODO: The backtrace should include inlinable_function_which_tail_calls.
+}
+
+void __attribute__((always_inline)) inlinable_function_which_tail_calls() {
+  tail_call_sink();
+}
+
+void __attribute__((noinline)) func3() {
+  inlinable_function_which_tail_calls();
+}
+
+void __attribute__((always_inline)) inline_sink() {
+  x++; //% self.filecheck("bt", "main.cpp", "-check-prefix=INLINE-SINK")
+  // INLINE-SINK: frame #0: 0x{{[0-9a-f]+}} a.out`func2() [inlined] inline_sink() at main.cpp:[[@LINE-1]]:4 [opt]
+  // INLINE-SINK-NEXT: func2{{.*}} [opt]
+  // INLINE-SINK-NEXT: func1{{.*}} [opt] [artificial]
+  // INLINE-SINK-NEXT: main{{.*}} [opt]
+}
+
+void __attribute__((noinline)) func2() { inline_sink(); /* inlined */ }
+
+void __attribute__((noinline)) func1() { func2(); /* tail */ }
+
+int __attribute__((disable_tail_calls)) main() {
+  // First, call a function that tail-calls a function, which itself inlines
+  // a third function.
+  func1();
+
+  // Next, call a function which contains an inlined tail-call.
+  func3();
+
+  return 0;
+}
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/sbapi_support/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/sbapi_support/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/sbapi_support/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/sbapi_support/TestTailCallFrameSBAPI.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/sbapi_support/TestTailCallFrameSBAPI.py
new file mode 100644
index 00000000000..0e475a4c006
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/sbapi_support/TestTailCallFrameSBAPI.py
@@ -0,0 +1,65 @@
+"""
+Test SB API support for identifying artificial (tail call) frames.
+"""
+
+import lldb
+import lldbsuite.test.lldbutil as lldbutil
+from lldbsuite.test.lldbtest import *
+
+class TestTailCallFrameSBAPI(TestBase):
+    mydir = TestBase.compute_mydir(__file__)
+
+    # If your test case doesn't stress debug info, the
+    # set this to true.  That way it won't be run once for
+    # each debug info format.
+    NO_DEBUG_INFO_TESTCASE = True
+
+    def test_tail_call_frame_sbapi(self):
+        self.build()
+        self.do_test()
+
+    def setUp(self):
+        # Call super's setUp().
+        TestBase.setUp(self)
+
+    def do_test(self):
+        exe = self.getBuildArtifact("a.out")
+
+        # Create a target by the debugger.
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+
+        breakpoint = target.BreakpointCreateBySourceRegex("break here",
+                lldb.SBFileSpec("main.cpp"))
+        self.assertTrue(breakpoint and
+                        breakpoint.GetNumLocations() == 1,
+                        VALID_BREAKPOINT)
+
+        error = lldb.SBError()
+        launch_info = lldb.SBLaunchInfo(None)
+        process = target.Launch(launch_info, error)
+        self.assertTrue(process, PROCESS_IS_VALID)
+
+        # Did we hit our breakpoint?
+        threads = lldbutil.get_threads_stopped_at_breakpoint(process,
+                breakpoint)
+        self.assertTrue(
+            len(threads) == 1,
+            "There should be a thread stopped at our breakpoint")
+
+        self.assertTrue(breakpoint.GetHitCount() == 1)
+
+        thread = threads[0]
+
+        # Here's what we expect to see in the backtrace:
+        #   frame #0: ... a.out`sink() at main.cpp:13:4 [opt]
+        #   frame #1: ... a.out`func3() at main.cpp:14:1 [opt] [artificial]
+        #   frame #2: ... a.out`func2() at main.cpp:18:62 [opt]
+        #   frame #3: ... a.out`func1() at main.cpp:18:85 [opt] [artificial]
+        #   frame #4: ... a.out`main at main.cpp:23:3 [opt]
+        names = ["sink()", "func3()", "func2()", "func1()", "main"]
+        artificiality = [False, True, False, True, False]
+        for idx, (name, is_artificial) in enumerate(zip(names, artificiality)):
+            frame = thread.GetFrameAtIndex(idx)
+            self.assertTrue(frame.GetDisplayFunctionName() == name)
+            self.assertTrue(frame.IsArtificial() == is_artificial)
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/sbapi_support/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/sbapi_support/main.cpp
new file mode 100644
index 00000000000..f9e84da5173
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/sbapi_support/main.cpp
@@ -0,0 +1,25 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) sink() {
+  x++; /* break here */
+}
+
+void __attribute__((noinline)) func3() { sink(); /* tail */ }
+
+void __attribute__((disable_tail_calls, noinline)) func2() { func3(); /* regular */ }
+
+void __attribute__((noinline)) func1() { func2(); /* tail */ }
+
+int __attribute__((disable_tail_calls)) main() {
+  func1(); /* regular */
+  return 0;
+}
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_message/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_message/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_message/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_message/TestArtificialFrameStepOutMessage.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_message/TestArtificialFrameStepOutMessage.py
new file mode 100644
index 00000000000..aec4d503fd7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_message/TestArtificialFrameStepOutMessage.py
@@ -0,0 +1,5 @@
+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals(),
+        [decorators.skipUnlessHasCallSiteInfo])
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_message/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_message/main.cpp
new file mode 100644
index 00000000000..f2f11365df7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_message/main.cpp
@@ -0,0 +1,28 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) sink() {
+  x++; //% self.filecheck("finish", "main.cpp", "-implicit-check-not=artificial")
+  // CHECK: stop reason = step out
+  // CHECK-NEXT: Stepped out past: frame #1: 0x{{[0-9a-f]+}} a.out`func3{{.*}} [opt] [artificial]
+  // CHECK: frame #0: 0x{{[0-9a-f]+}} a.out`func2{{.*}} [opt]
+}
+
+void __attribute__((noinline)) func3() { sink(); /* tail */ }
+
+void __attribute__((disable_tail_calls, noinline)) func2() { func3(); /* regular */ }
+
+void __attribute__((noinline)) func1() { func2(); /* tail */ }
+
+int __attribute__((disable_tail_calls)) main() {
+  func1(); /* regular */
+  return 0;
+}
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_or_return/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_or_return/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_or_return/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_or_return/TestSteppingOutWithArtificialFrames.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_or_return/TestSteppingOutWithArtificialFrames.py
new file mode 100644
index 00000000000..c1806f62ef7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_or_return/TestSteppingOutWithArtificialFrames.py
@@ -0,0 +1,92 @@
+"""
+Test SB API support for identifying artificial (tail call) frames.
+"""
+
+import lldb
+import lldbsuite.test.lldbutil as lldbutil
+from lldbsuite.test.lldbtest import *
+
+class TestArtificialFrameThreadStepOut1(TestBase):
+    mydir = TestBase.compute_mydir(__file__)
+
+    # If your test case doesn't stress debug info, the
+    # set this to true.  That way it won't be run once for
+    # each debug info format.
+    NO_DEBUG_INFO_TESTCASE = True
+
+    def prepare_thread(self):
+        exe = self.getBuildArtifact("a.out")
+
+        # Create a target by the debugger.
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+
+        breakpoint = target.BreakpointCreateBySourceRegex("break here",
+                lldb.SBFileSpec("main.cpp"))
+        self.assertTrue(breakpoint and
+                        breakpoint.GetNumLocations() == 1,
+                        VALID_BREAKPOINT)
+
+        error = lldb.SBError()
+        launch_info = lldb.SBLaunchInfo(None)
+        process = target.Launch(launch_info, error)
+        self.assertTrue(process, PROCESS_IS_VALID)
+
+        # Did we hit our breakpoint?
+        threads = lldbutil.get_threads_stopped_at_breakpoint(process,
+                breakpoint)
+        self.assertTrue(
+            len(threads) == 1,
+            "There should be a thread stopped at our breakpoint")
+
+        self.assertTrue(breakpoint.GetHitCount() == 1)
+
+        thread = threads[0]
+
+        # Here's what we expect to see in the backtrace:
+        #   frame #0: ... a.out`sink() at main.cpp:13:4 [opt]
+        #   frame #1: ... a.out`func3() at main.cpp:14:1 [opt] [artificial]
+        #   frame #2: ... a.out`func2() at main.cpp:18:62 [opt]
+        #   frame #3: ... a.out`func1() at main.cpp:18:85 [opt] [artificial]
+        #   frame #4: ... a.out`main at main.cpp:23:3 [opt]
+        return thread
+
+    def test_stepping_out_past_artificial_frame(self):
+        self.build()
+        thread = self.prepare_thread()
+
+        # Frame #0's ancestor is artificial. Stepping out should move to
+        # frame #2, because we behave as-if artificial frames were not present.
+        thread.StepOut()
+        frame2 = thread.GetSelectedFrame()
+        self.assertTrue(frame2.GetDisplayFunctionName() == "func2()")
+        self.assertFalse(frame2.IsArtificial())
+
+        # Ditto: stepping out of frame #2 should move to frame #4.
+        thread.StepOut()
+        frame4 = thread.GetSelectedFrame()
+        self.assertTrue(frame4.GetDisplayFunctionName() == "main")
+        self.assertFalse(frame2.IsArtificial())
+
+    def test_return_past_artificial_frame(self):
+        self.build()
+        thread = self.prepare_thread()
+
+        value = lldb.SBValue()
+
+        # Frame #0's ancestor is artificial. Returning from frame #0 should move
+        # to frame #2.
+        thread.ReturnFromFrame(thread.GetSelectedFrame(), value)
+        frame2 = thread.GetSelectedFrame()
+        self.assertTrue(frame2.GetDisplayFunctionName() == "func2()")
+        self.assertFalse(frame2.IsArtificial())
+
+        # Ditto: stepping out of frame #2 should move to frame #4.
+        thread.ReturnFromFrame(thread.GetSelectedFrame(), value)
+        frame4 = thread.GetSelectedFrame()
+        self.assertTrue(frame4.GetDisplayFunctionName() == "main")
+        self.assertFalse(frame2.IsArtificial())
+
+    def setUp(self):
+        # Call super's setUp().
+        TestBase.setUp(self)
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_or_return/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_or_return/main.cpp
new file mode 100644
index 00000000000..f7a81873906
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/thread_step_out_or_return/main.cpp
@@ -0,0 +1,25 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) sink() {
+  x++; // break here
+}
+
+void __attribute__((noinline)) func3() { sink(); /* tail */ }
+
+void __attribute__((disable_tail_calls, noinline)) func2() { func3(); /* regular */ }
+
+void __attribute__((noinline)) func1() { func2(); /* tail */ }
+
+int __attribute__((disable_tail_calls)) main() {
+  func1(); /* regular */
+  return 0;
+}
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/Makefile b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/Makefile
new file mode 100644
index 00000000000..15bc2e7f415
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/Makefile
@@ -0,0 +1,4 @@
+LEVEL = ../../../make
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules
+CXXFLAGS += -g -O1 -glldb
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/TestUnambiguousTailCalls.py b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/TestUnambiguousTailCalls.py
new file mode 100644
index 00000000000..aec4d503fd7
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/TestUnambiguousTailCalls.py
@@ -0,0 +1,5 @@
+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(__file__, globals(),
+        [decorators.skipUnlessHasCallSiteInfo])
diff --git a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/main.cpp b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/main.cpp
new file mode 100644
index 00000000000..c180d45b9de
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/main.cpp
@@ -0,0 +1,30 @@
+//===-- main.cpp ------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+volatile int x;
+
+void __attribute__((noinline)) sink() {
+  x++; //% self.filecheck("bt", "main.cpp", "-implicit-check-not=artificial")
+  // CHECK: frame #0: 0x{{[0-9a-f]+}} a.out`sink() at main.cpp:[[@LINE-1]]:4 [opt]
+  // CHECK-NEXT: frame #1: 0x{{[0-9a-f]+}} a.out`func3{{.*}} [opt] [artificial]
+  // CHECK-NEXT: frame #2: 0x{{[0-9a-f]+}} a.out`func2{{.*}} [opt]
+  // CHECK-NEXT: frame #3: 0x{{[0-9a-f]+}} a.out`func1{{.*}} [opt] [artificial]
+  // CHECK-NEXT: frame #4: 0x{{[0-9a-f]+}} a.out`main{{.*}} [opt]
+}
+
+void __attribute__((noinline)) func3() { sink(); /* tail */ }
+
+void __attribute__((disable_tail_calls, noinline)) func2() { func3(); /* regular */ }
+
+void __attribute__((noinline)) func1() { func2(); /* tail */ }
+
+int __attribute__((disable_tail_calls)) main() {
+  func1(); /* regular */
+  return 0;
+}