2 files changed, 21 insertions, 9 deletions
diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index 421e7deccc3..dd87dd4657e 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -106,15 +106,6 @@ AppendBytes(CharUnits FieldOffsetInChars, llvm::Constant *InitCst) {
   CharUnits AlignedNextFieldOffsetInChars =
     NextFieldOffsetInChars.RoundUpToAlignment(FieldAlignment);
 
-  if (AlignedNextFieldOffsetInChars > FieldOffsetInChars) {
-    assert(!Packed && "Alignment is wrong even with a packed struct!");
-
-    // Convert the struct to a packed struct.
-    ConvertStructToPacked();
-
-    AlignedNextFieldOffsetInChars = NextFieldOffsetInChars;
-  }
-
   if (AlignedNextFieldOffsetInChars < FieldOffsetInChars) {
     // We need to append padding.
     AppendPadding(FieldOffsetInChars - NextFieldOffsetInChars);
@@ -122,6 +113,16 @@ AppendBytes(CharUnits FieldOffsetInChars, llvm::Constant *InitCst) {
     assert(NextFieldOffsetInChars == FieldOffsetInChars &&
            "Did not add enough padding!");
 
+    AlignedNextFieldOffsetInChars =
+      NextFieldOffsetInChars.RoundUpToAlignment(FieldAlignment);
+  }
+
+  if (AlignedNextFieldOffsetInChars > FieldOffsetInChars) {
+    assert(!Packed && "Alignment is wrong even with a packed struct!");
+
+    // Convert the struct to a packed struct.
+    ConvertStructToPacked();
+
     AlignedNextFieldOffsetInChars = NextFieldOffsetInChars;
   }
 
diff --git a/clang/test/CodeGen/const-init.c b/clang/test/CodeGen/const-init.c
index 7d7ccae370d..ccc6604c456 100644
--- a/clang/test/CodeGen/const-init.c
+++ b/clang/test/CodeGen/const-init.c
@@ -159,3 +159,14 @@ void g29() {
   static int b[1] = { "asdf" }; // expected-warning {{incompatible pointer to integer conversion initializing 'int' with an expression of type 'char [5]'}}
   static int c[1] = { L"a" };
 }
+
+// PR21300
+void g30() {
+#pragma pack(1)
+  static struct {
+    int : 1;
+    int x;
+  } a = {};
+  // CHECK: @g30.a = internal global %struct.anon.1 <{ i8 undef, i32 0 }>, align 1
+#pragma pack()
+}