diff --git a/clang/include/clang/Basic/Builtins.def b/clang/include/clang/Basic/Builtins.def
--- a/clang/include/clang/Basic/Builtins.def
+++ b/clang/include/clang/Basic/Builtins.def
@@ -1480,6 +1480,7 @@
 BUILTIN(__builtin_char_memchr, "c*cC*iz", "n")
 BUILTIN(__builtin_dump_struct, "ivC*v*", "tn")
 BUILTIN(__builtin_preserve_access_index, "v.", "t")
+BUILTIN(__builtin_get_cpu_cache_line_size, "zv", "nc")
 
 // Alignment builtins (uses custom parsing to support pointers and integers)
 BUILTIN(__builtin_is_aligned, "bvC*z", "nct")
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -10915,6 +10915,14 @@
     return Success(Info.InConstantContext, E);
   }
 
+  case Builtin::BI__builtin_get_cpu_cache_line_size: {
+    Optional<unsigned> cacheLineSize =
+      Info.Ctx.getTargetInfo().getCPUCacheLineSize();
+    if (cacheLineSize.hasValue())
+      return Success(cacheLineSize.getValue(), E);
+    return Success(0, E);
+  }
+
   case Builtin::BI__builtin_ctz:
   case Builtin::BI__builtin_ctzl:
   case Builtin::BI__builtin_ctzll:
diff --git a/clang/test/SemaCXX/builtin-cache-line-size.cpp b/clang/test/SemaCXX/builtin-cache-line-size.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/builtin-cache-line-size.cpp
@@ -0,0 +1,32 @@
+// RUN: %clang -mcpu=i368 %s
+// RUN: ./a.out
+
+#include <cassert>
+
+size_t a() {
+  return __builtin_get_cpu_cache_line_size();
+}
+
+size_t b(bool x) {
+  if (x) {
+    return __builtin_get_cpu_cache_line_size();
+  }
+  return 0;
+}
+
+int main() {
+  assert(a() == 64);
+  assert(b(true) == 64);
+  assert(b(false) == 0);
+}
+
+// This is based on the value for i368.
+static_assert(__builtin_get_cpu_cache_line_size() == 64, "");
+
+struct keep_apart {
+  alignas(__builtin_get_cpu_cache_line_size()) int cat;
+  alignas(__builtin_get_cpu_cache_line_size()) int dog;
+};
+
+static_assert(sizeof(keep_apart) == __builtin_get_cpu_cache_line_size() * 2 ||
+              __builtin_get_cpu_cache_line_size() == 0, "");