Index: lib/AST/RecordLayoutBuilder.cpp
===================================================================
--- lib/AST/RecordLayoutBuilder.cpp
+++ lib/AST/RecordLayoutBuilder.cpp
@@ -632,6 +632,9 @@
   /// pointer, as opposed to inheriting one from a primary base class.
   bool HasOwnVFPtr;
 
+  /// \brief the flag of field offset changing due to packed attribute.
+  bool HasPackedField;
+
   typedef llvm::DenseMap<const CXXRecordDecl *, CharUnits> BaseOffsetsMapTy;
 
   /// Bases - base classes and their offsets in the record.
@@ -666,7 +669,7 @@
         NonVirtualSize(CharUnits::Zero()),
         NonVirtualAlignment(CharUnits::One()), PrimaryBase(nullptr),
         PrimaryBaseIsVirtual(false), HasOwnVFPtr(false),
-        FirstNearlyEmptyVBase(nullptr) {}
+        HasPackedField(false), FirstNearlyEmptyVBase(nullptr) {}
 
   void Layout(const RecordDecl *D);
   void Layout(const CXXRecordDecl *D);
@@ -1847,7 +1850,6 @@
   uint64_t UnpaddedSize = getSizeInBits() - UnfilledBitsInLastUnit;
   uint64_t UnpackedSizeInBits =
       llvm::alignTo(getSizeInBits(), Context.toBits(UnpackedAlignment));
-  CharUnits UnpackedSize = Context.toCharUnitsFromBits(UnpackedSizeInBits);
   uint64_t RoundedSize =
       llvm::alignTo(getSizeInBits(), Context.toBits(Alignment));
 
@@ -1882,10 +1884,11 @@
           << (InBits ? 1 : 0); // (byte|bit)
     }
 
-    // Warn if we packed it unnecessarily. If the alignment is 1 byte don't
-    // bother since there won't be alignment issues.
-    if (Packed && UnpackedAlignment > CharUnits::One() && 
-        getSize() == UnpackedSize)
+    // Warn if we packed it unnecessarily, when the unpacked alignment is not
+    // greater than the one after packing, the size in bits doesn't change and
+    // the offset of each field is identical.
+    if (Packed && UnpackedAlignment <= Alignment &&
+        UnpackedSizeInBits == getSizeInBits() && !HasPackedField)
       Diag(D->getLocation(), diag::warn_unnecessary_packed)
           << Context.getTypeDeclType(RD);
   }
@@ -1977,13 +1980,10 @@
           << Context.getTypeDeclType(D->getParent())
           << PadSize
           << (InBits ? 1 : 0); // (byte|bit)
-  }
-
-  // Warn if we packed it unnecessarily. If the alignment is 1 byte don't
-  // bother since there won't be alignment issues.
-  if (isPacked && UnpackedAlign > CharBitNum && Offset == UnpackedOffset)
-    Diag(D->getLocation(), diag::warn_unnecessary_packed)
-        << D->getIdentifier();
+ }
+ if (isPacked && Offset != UnpackedOffset) {
+   HasPackedField = true;
+ }
 }
 
 static const CXXMethodDecl *computeKeyFunction(ASTContext &Context,
Index: test/CodeGenCXX/warn-padded-packed.cpp
===================================================================
--- test/CodeGenCXX/warn-padded-packed.cpp
+++ test/CodeGenCXX/warn-padded-packed.cpp
@@ -17,7 +17,7 @@
 } __attribute__((packed));
 
 struct S4 {
-  int i; // expected-warning {{packed attribute is unnecessary for 'i'}}
+  int i;
   char c;
 } __attribute__((packed));
 
@@ -46,18 +46,18 @@
   int i; // expected-warning {{padding struct 'S8' with 3 bytes to align 'i'}}
 };
 
-struct S9 { // expected-warning {{packed attribute is unnecessary for 'S9'}}
-  int x; // expected-warning {{packed attribute is unnecessary for 'x'}}
-  int y; // expected-warning {{packed attribute is unnecessary for 'y'}}
+struct S9 {
+  int x;
+  int y;
 } __attribute__((packed));
 
-struct S10 { // expected-warning {{packed attribute is unnecessary for 'S10'}}
-  int x; // expected-warning {{packed attribute is unnecessary for 'x'}}
+struct S10 {
+  int x;
   char a,b,c,d;
 } __attribute__((packed));
 
 
-struct S11 {
+struct S11 { // expected-warning {{packed attribute is unnecessary for 'S11'}}
   bool x;
   char a,b,c,d;
 } __attribute__((packed));
@@ -72,5 +72,82 @@
   bool b : 10;
 };
 
+struct S14 { // expected-warning {{packed attribute is unnecessary for 'S14'}}
+  char a,b,c,d;
+} __attribute__((packed));
+
+struct S15 { // expected-warning {{packed attribute is unnecessary for 'S15'}}
+  struct S14 s;
+  char a;
+} __attribute__((packed));
+
+struct S16 { // expected-warning {{padding size of 'S16' with 2 bytes to alignment boundary}} expected-warning {{packed attribute is unnecessary for 'S16'}}
+  char a,b;
+} __attribute__((packed, aligned(4)));
+
+struct S17 {
+  struct S16 s;
+  char a,b;
+} __attribute__((packed, aligned(2)));
+
+struct S18 { // expected-warning {{padding size of 'S18' with 2 bytes to alignment boundary}} expected-warning {{packed attribute is unnecessary for 'S18'}}
+  struct S16 s;
+  char a,b;
+} __attribute__((packed, aligned(4)));
+
+struct S19 { // expected-warning {{packed attribute is unnecessary for 'S19'}}
+  bool b;
+  char a;
+} __attribute__((packed, aligned(1)));
+
+struct S20 {
+  int i;
+  char a;
+} __attribute__((packed, aligned(1)));
+
+struct S21 { // expected-warning {{padding size of 'S21' with 4 bits to alignment boundary}}
+  unsigned char a : 6;
+  unsigned char b : 6;
+} __attribute__((packed, aligned(1)));
+
+struct S22 { // expected-warning {{packed attribute is unnecessary for 'S22'}}
+  unsigned char a : 4;
+  unsigned char b : 4;
+} __attribute__((packed));
+
+struct S23 { // expected-warning {{padding size of 'S23' with 4 bits to alignment boundary}} expected-warning {{packed attribute is unnecessary for 'S23'}}
+  unsigned char a : 2;
+  unsigned char b : 2;
+} __attribute__((packed));
+
+struct S24 {
+  unsigned char a : 6;
+  unsigned char b : 6;
+  unsigned char c : 6;
+  unsigned char d : 6;
+  unsigned char e : 6;
+  unsigned char f : 6;
+  unsigned char g : 6;
+  unsigned char h : 6;
+} __attribute__((packed));
+
+struct S25 { // expected-warning {{padding size of 'S25' with 7 bits to alignment boundary}} expected-warning {{packed attribute is unnecessary for 'S25'}}
+  unsigned char a;
+  unsigned char b : 1;
+} __attribute__((packed));
+
+struct S26 { // expected-warning {{packed attribute is unnecessary for 'S26'}}
+  unsigned char a : 1;
+  unsigned char b; //expected-warning {{padding struct 'S26' with 7 bits to align 'b'}}
+} __attribute__((packed));
+
+struct S27 { // expected-warning {{padding size of 'S27' with 7 bits to alignment boundary}}
+  unsigned char a : 1;
+  unsigned char b : 8;
+} __attribute__((packed));
+
+
 // The warnings are emitted when the layout of the structs is computed, so we have to use them.
-void f(S1*, S2*, S3*, S4*, S5*, S6*, S7*, S8*, S9*, S10*, S11*, S12*, S13*) { }
+void f(S1*, S2*, S3*, S4*, S5*, S6*, S7*, S8*, S9*, S10*, S11*, S12*, S13*,
+       S14*, S15*, S16*, S17*, S18*, S19*, S20*, S21*, S22*, S23*, S24*, S25*,
+       S26*, S27*){}