commit 20208cc046c206a1436edb714e94bd52a0bc8572
author Momchil Velikov <momchil.velikov@arm.com> Mon Jul 30 17:48:23 2018 +0000
committer Momchil Velikov <momchil.velikov@arm.com> Mon Jul 30 17:48:23 2018 +0000
tree 24548919809d313e32c81ace99e7da457dbf1d1b
parent fa3bee47569b1583e4319bbdbcd3f129345caa25

[ARM, AArch64]: Use unadjusted alignment when passing composites as arguments

The "Procedure Call Procedure Call Standard for the ARM® Architecture"
(https://static.docs.arm.com/ihi0042/f/IHI0042F_aapcs.pdf), specifies that
composite types are passed according to their "natural alignment", i.e. the
alignment before alignment adjustment on the entire composite is applied.

The same applies for AArch64 ABI.

Clang, however, used the adjusted alignment.

GCC already implements the ABI correctly. With this patch Clang becomes
compatible with GCC and passes such arguments in accordance with AAPCS.

Differential Revision: https://reviews.llvm.org/D46013

llvm-svn: 338279

clang/lib/AST/RecordLayoutBuilder.cpp

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index b4b09c7c..c92ac20 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -582,6 +582,9 @@
   /// The alignment if attribute packed is not used.
   CharUnits UnpackedAlignment;
 
+  /// \brief The maximum of the alignments of top-level members.
+  CharUnits UnadjustedAlignment;
+
   SmallVector<uint64_t, 16> FieldOffsets;
 
   /// Whether the external AST source has provided a layout for this
@@ -662,6 +665,7 @@
                              EmptySubobjectMap *EmptySubobjects)
       : Context(Context), EmptySubobjects(EmptySubobjects), Size(0),
         Alignment(CharUnits::One()), UnpackedAlignment(CharUnits::One()),
+        UnadjustedAlignment(CharUnits::One()),
         UseExternalLayout(false), InferAlignment(false), Packed(false),
         IsUnion(false), IsMac68kAlign(false), IsMsStruct(false),
         UnfilledBitsInLastUnit(0), LastBitfieldTypeSize(0),
@@ -1707,7 +1711,9 @@
   setSize(std::max(getSizeInBits(), getDataSizeInBits()));
 
   // Remember max struct/class alignment.
-  UpdateAlignment(Context.toCharUnitsFromBits(FieldAlign), 
+  UnadjustedAlignment =
+      std::max(UnadjustedAlignment, Context.toCharUnitsFromBits(FieldAlign));
+  UpdateAlignment(Context.toCharUnitsFromBits(FieldAlign),
                   Context.toCharUnitsFromBits(UnpackedFieldAlign));
 }
 
@@ -1862,6 +1868,7 @@
   setSize(std::max(getSizeInBits(), getDataSizeInBits()));
 
   // Remember max struct/class alignment.
+  UnadjustedAlignment = std::max(UnadjustedAlignment, FieldAlign);
   UpdateAlignment(FieldAlign, UnpackedFieldAlign);
 }
 
@@ -2988,7 +2995,8 @@
     if (const auto *RD = dyn_cast<CXXRecordDecl>(D)) {
       Builder.cxxLayout(RD);
       NewEntry = new (*this) ASTRecordLayout(
-          *this, Builder.Size, Builder.Alignment, Builder.RequiredAlignment,
+          *this, Builder.Size, Builder.Alignment, Builder.Alignment,
+          Builder.RequiredAlignment,
           Builder.HasOwnVFPtr, Builder.HasOwnVFPtr || Builder.PrimaryBase,
           Builder.VBPtrOffset, Builder.DataSize, Builder.FieldOffsets,
           Builder.NonVirtualSize, Builder.Alignment, CharUnits::Zero(),
@@ -2998,7 +3006,8 @@
     } else {
       Builder.layout(D);
       NewEntry = new (*this) ASTRecordLayout(
-          *this, Builder.Size, Builder.Alignment, Builder.RequiredAlignment,
+          *this, Builder.Size, Builder.Alignment, Builder.Alignment,
+          Builder.RequiredAlignment,
           Builder.Size, Builder.FieldOffsets);
     }
   } else {
@@ -3019,7 +3028,7 @@
       CharUnits NonVirtualSize =
           skipTailPadding ? DataSize : Builder.NonVirtualSize;
       NewEntry = new (*this) ASTRecordLayout(
-          *this, Builder.getSize(), Builder.Alignment,
+          *this, Builder.getSize(), Builder.Alignment, Builder.UnadjustedAlignment,
           /*RequiredAlignment : used by MS-ABI)*/
           Builder.Alignment, Builder.HasOwnVFPtr, RD->isDynamicClass(),
           CharUnits::fromQuantity(-1), DataSize, Builder.FieldOffsets,
@@ -3032,7 +3041,7 @@
       Builder.Layout(D);
 
       NewEntry = new (*this) ASTRecordLayout(
-          *this, Builder.getSize(), Builder.Alignment,
+          *this, Builder.getSize(), Builder.Alignment, Builder.UnadjustedAlignment,
           /*RequiredAlignment : used by MS-ABI)*/
           Builder.Alignment, Builder.getSize(), Builder.FieldOffsets);
     }
@@ -3186,6 +3195,7 @@
   const ASTRecordLayout *NewEntry =
     new (*this) ASTRecordLayout(*this, Builder.getSize(),
                                 Builder.Alignment,
+                                Builder.UnadjustedAlignment,
                                 /*RequiredAlignment : used by MS-ABI)*/
                                 Builder.Alignment,
                                 Builder.getDataSize(),