Use arrays as union padding. Also, since the resulting struct will always contain a single element and either a single i8 element or an array of i8s, there's no reason to use a packed struct.

llvm-svn: 76854

2 files changed, 12 insertions, 9 deletions

diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index 4f1f58fefda..43284b51730 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -243,15 +243,18 @@ public:
     Types.push_back(C->getType());
     unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
     unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(Ty);
-    while (CurSize < TotalSize) {
-      Elts.push_back(VMContext.getNullValue(llvm::Type::Int8Ty));
-      Types.push_back(llvm::Type::Int8Ty);
-      CurSize++;
+
+    assert(CurSize <= TotalSize && "Union size mismatch!");
+    if (unsigned NumPadBytes = TotalSize - CurSize) {
+      const llvm::Type *Ty = llvm::Type::Int8Ty;
+      if (NumPadBytes > 1)
+        Ty = VMContext.getArrayType(Ty, NumPadBytes);
+
+      Elts.push_back(VMContext.getNullValue(Ty));
+      Types.push_back(Ty);
     }
 
-    // This always generates a packed struct
-    // FIXME: Try to generate an unpacked struct when we can
-    llvm::StructType* STy = VMContext.getStructType(Types, true);
+    llvm::StructType* STy = VMContext.getStructType(Types, false);
     return VMContext.getConstantStruct(STy, Elts);
   }
 
diff --git a/clang/test/CodeGen/cast-to-union.c b/clang/test/CodeGen/cast-to-union.c
index 6098bcc5a07..39644c0c997 100644
--- a/clang/test/CodeGen/cast-to-union.c
+++ b/clang/test/CodeGen/cast-to-union.c
@@ -1,7 +1,7 @@
 // RUN: clang-cc -emit-llvm < %s -o %t &&
 // RUN: grep "store i32 351, i32*" %t &&
-// RUN: grep "w = global %0 <{ i32 2, i8 0, i8 0, i8 0, i8 0 }>" %t &&
-// RUN: grep "y = global %1 <{ double 7.300000e+01 }>" %t
+// RUN: grep "w = global %0 { i32 2, \[4 x i8\] zeroinitializer }" %t &&
+// RUN: grep "y = global %1 { double 7.300000e+01 }" %t
 
 union u { int i; double d; };