Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -1566,6 +1566,13 @@
   }
 }
 
+static unsigned maxNestingDepth(const AnnotatedLine &Line) {
+  unsigned Result = 0;
+  for (const auto* Tok = Line.First; Tok != nullptr; Tok = Tok->Next)
+    Result = std::max(Result, Tok->NestingLevel);
+  return Result;
+}
+
 void TokenAnnotator::annotate(AnnotatedLine &Line) {
   for (SmallVectorImpl<AnnotatedLine *>::iterator I = Line.Children.begin(),
                                                   E = Line.Children.end();
@@ -1574,6 +1581,14 @@
   }
   AnnotatingParser Parser(Style, Line, Keywords);
   Line.Type = Parser.parseLine();
+
+  // With very deep nesting, ExpressionParser uses lots of stack and the
+  // formatting algorithm is very slow. We're not going to do a good job here
+  // anyway - it's probably generated code being formatted by mistake.
+  // Just skip the whole line.
+  if (maxNestingDepth(Line) > 50)
+    Line.Type = LT_Invalid;
+
   if (Line.Type == LT_Invalid)
     return;
 
Index: unittests/Format/FormatTest.cpp
===================================================================
--- unittests/Format/FormatTest.cpp
+++ unittests/Format/FormatTest.cpp
@@ -7179,6 +7179,30 @@
   verifyFormat("operator");
 }
 
+TEST_F(FormatTest, SkipsDeeplyNestedLines) {
+  // This code would be painfully slow to format if we didn't skip it.
+  std::string Code("A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(\n" // 20x
+                   "A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(\n"
+                   "A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(\n"
+                   "A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(\n"
+                   "A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(A(\n"
+                   "A(1, 1)\n"
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1)\n" // 10x
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1)\n"
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1)\n"
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1)\n"
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1)\n"
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1)\n"
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1)\n"
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1)\n"
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1)\n"
+                   ", 1), 1), 1), 1), 1), 1), 1), 1), 1), 1);\n");
+  // Deeply nested part is untouched, rest is formatted.
+  EXPECT_EQ(std::string("int i;\n") + Code + "int j;\n",
+            format(std::string("int    i;\n") + Code + "int    j;\n",
+                   getLLVMStyle(), IC_ExpectIncomplete));
+}
+
 //===----------------------------------------------------------------------===//
 // Objective-C tests.
 //===----------------------------------------------------------------------===//