No need to add tail padding if the resulting LLVM struct type will have the same size as the final record size.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@90820 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 14 insertions, 4 deletions

diff --git a/lib/CodeGen/CGRecordLayoutBuilder.cpp b/lib/CodeGen/CGRecordLayoutBuilder.cpp
index 1a9bc39170..31784eda5a 100644
--- a/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -88,8 +88,6 @@ void CGRecordLayoutBuilder::LayoutBitField(const FieldDecl *D,
 
   AppendBytes(NumBytesToAppend);
 
-  AlignmentAsLLVMStruct = std::max(AlignmentAsLLVMStruct, getTypeAlignment(Ty));
-
   BitsAvailableInLastField =
     NextFieldOffsetInBytes * 8 - (FieldOffset + FieldSize);
 }
@@ -247,6 +245,14 @@ void CGRecordLayoutBuilder::AppendTailPadding(uint64_t RecordSize) {
   uint64_t RecordSizeInBytes = RecordSize / 8;
   assert(NextFieldOffsetInBytes <= RecordSizeInBytes && "Size mismatch!");
 
+  uint64_t AlignedNextFieldOffset = 
+    llvm::RoundUpToAlignment(NextFieldOffsetInBytes, AlignmentAsLLVMStruct);
+
+  if (AlignedNextFieldOffset == RecordSizeInBytes) {
+    // We don't need any padding.
+    return;
+  }
+  
   unsigned NumPadBytes = RecordSizeInBytes - NextFieldOffsetInBytes;
   AppendBytes(NumPadBytes);
 }
diff --git a/test/CodeGenCXX/class-layout.cpp b/test/CodeGenCXX/class-layout.cpp
index 7663d2e541..d4fc627082 100644
--- a/test/CodeGenCXX/class-layout.cpp
+++ b/test/CodeGenCXX/class-layout.cpp
@@ -1,5 +1,9 @@
-// RUN: clang-cc %s -emit-llvm -o %t
+// RUN: clang-cc %s -emit-llvm -o - | FileCheck %s
 
 // An extra byte shoudl be allocated for an empty class.
-// RUN: grep '%.truct.A = type { i8 }' %t
+// CHECK: %struct.A = type { i8 }
 struct A { } a;
+
+// No need to add tail padding here.
+// CHECK: %struct.B = type { i8*, i32 }
+struct B { void *a; int b; } b;