[clang] b8f612e - [PowerPC][AIX] Packed zero-width bitfields do not affect alignment.

[Sean Fertile via cfe-commits]

Author: Sean Fertile
Date: 2021-08-04T11:03:25-04:00
New Revision: b8f612e780e50cfb62bc0196b6367e4587949f88

URL: https://github.com/llvm/llvm-project/commit/b8f612e780e50cfb62bc0196b6367e4587949f88
DIFF: https://github.com/llvm/llvm-project/commit/b8f612e780e50cfb62bc0196b6367e4587949f88.diff

LOG: [PowerPC][AIX] Packed zero-width bitfields do not affect alignment.

Zero-width bitfields on AIX pad out to the natral alignment boundary but
do not change the containing records alignment.

Differential Revision: https://reviews.llvm.org/D106900

Added: 
    

Modified: 
    clang/lib/AST/RecordLayoutBuilder.cpp
    clang/test/Layout/aix-packed-bitfields.c

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 972690becf9ec..83045253aa512 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -1775,11 +1775,18 @@ void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
       !D->getIdentifier())
     FieldAlign = UnpackedFieldAlign = 1;
 
-  // On AIX, zero-width bitfields pad out to the alignment boundary, but then
-  // do not affect overall record alignment if there is a pragma pack or
-  // pragma align(packed).
-  if (isAIXLayout(Context) && !MaxFieldAlignment.isZero() && !FieldSize)
-    FieldAlign = std::min(FieldAlign, MaxFieldAlignmentInBits);
+  // On AIX, zero-width bitfields pad out to the natural alignment boundary,
+  // but do not increase the alignment greater than the MaxFieldAlignment, or 1
+  // if packed.
+  if (isAIXLayout(Context) && !FieldSize) {
+    if (FieldPacked)
+      FieldAlign = 1;
+    if (!MaxFieldAlignment.isZero()) {
+      UnpackedFieldAlign =
+          std::min(UnpackedFieldAlign, MaxFieldAlignmentInBits);
+      FieldAlign = std::min(FieldAlign, MaxFieldAlignmentInBits);
+    }
+  }
 
   // Diagnose 
diff erences in layout due to padding or packing.
   if (!UseExternalLayout)

diff  --git a/clang/test/Layout/aix-packed-bitfields.c b/clang/test/Layout/aix-packed-bitfields.c
index 9bc907af0f596..88f6b3fced80a 100644
--- a/clang/test/Layout/aix-packed-bitfields.c
+++ b/clang/test/Layout/aix-packed-bitfields.c
@@ -1,14 +1,18 @@
 // RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -fdump-record-layouts \
-// RUN:     -fsyntax-only -fxl-pragma-pack -x c %s | FileCheck  %s
+// RUN:     -fsyntax-only -fxl-pragma-pack -x c %s | \
+// RUN:   FileCheck --check-prefixes=CHECK,32BIT %s
 
 // RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -fdump-record-layouts \
-// RUN:     -fsyntax-only -fxl-pragma-pack -x c++ %s | FileCheck %s
-//
+// RUN:     -fsyntax-only -fxl-pragma-pack -x c++ %s | \
+// RUN:   FileCheck --check-prefixes=CHECK,32BIT %s
+
 // RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -fdump-record-layouts \
-// RUN:     -fsyntax-only -fxl-pragma-pack -x c %s | FileCheck  %s
-//
+// RUN:     -fsyntax-only -fxl-pragma-pack -x c %s | \
+// RUN:   FileCheck --check-prefixes=CHECK,64BIT %s
+
 // RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -fdump-record-layouts \
-// RUN:     -fsyntax-only -fxl-pragma-pack -x c++ %s | FileCheck %s
+// RUN:     -fsyntax-only -fxl-pragma-pack -x c++ %s | \
+// RUN:   FileCheck --check-prefixes=CHECK,64BIT %s
 
 struct A {
   int a1 : 30;
@@ -75,3 +79,35 @@ int d = sizeof(struct Pack2);
 // CHECK-NEXT: 3:6-35 |   int a2
 // CHECK-NEXT:  7:4-7 |   int a3
 // CHECK-NEXT:          sizeof=8, {{(dsize=8, )?}}align=2, preferredalign=2
+//
+struct __attribute__((packed)) PackedAttr {
+  char f1;
+  int : 0;
+  short : 3;
+  char f4 : 2;
+};
+
+int e = sizeof(struct PackedAttr);
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:      0 | struct PackedAttr
+// CHECK-NEXT:      0 |   char f1
+// CHECK-NEXT:    4:- |   int
+// CHECK-NEXT:  4:0-2 |   short
+// CHECK-NEXT:  4:3-4 |   char f4
+// CHECK-NEXT:          sizeof=5, {{(dsize=5, )?}}align=1, preferredalign=1
+
+#pragma pack(2)
+struct __attribute__((packed)) PackedAttrAndPragma {
+  char f1;
+  long long : 0;
+};
+#pragma pack(pop)
+
+int f = sizeof(struct PackedAttrAndPragma);
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:      0 | struct PackedAttrAndPragma
+// CHECK-NEXT:      0 |   char f1
+// 32BIT-NEXT:    4:- |   long long
+// 32BIT-NEXT:          sizeof=4, {{(dsize=4, )?}}align=1, preferredalign=1
+// 64BIT-NEXT:    8:- |   long long
+// 64BIT-NEXT:          sizeof=8, {{(dsize=8, )?}}align=1, preferredalign=1