Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -14281,6 +14281,11 @@
       }
     }
 
+    if (SourceBT && SourceBT->isInteger() && TargetBT &&
+        TargetBT->isInteger()) {
+      return;
+    }
+
     // Fall through for non-constants to give a sign conversion warning.
   }
 
Index: clang/test/Sema/sign-conversion.c
===================================================================
--- clang/test/Sema/sign-conversion.c
+++ clang/test/Sema/sign-conversion.c
@@ -5,4 +5,8 @@
 void test(int x) {
   unsigned t0 = x; // expected-warning {{implicit conversion changes signedness}}
   unsigned t1 = (t0 == 5 ? x : 0); // expected-warning {{operand of ? changes signedness}}
+
+  // Clang has special treatment for left shift of literal '1'.
+  // Make sure there is no diagnostics.
+  long t2 = 1LL << x;
 }