r326173 - [RecordLayout] Don't align to non-power-of-2 sizes when using -mms-bitfields

[Martin Storsjo via cfe-commits]

Author: mstorsjo
Date: Mon Feb 26 22:27:06 2018
New Revision: 326173

URL: http://llvm.org/viewvc/llvm-project?rev=326173&view=rev
Log:
[RecordLayout] Don't align to non-power-of-2 sizes when using -mms-bitfields

When targeting GNU/MinGW for i386, the size of the "long double" data
type is 12 bytes (while it is 8 bytes in MSVC). When building
with -mms-bitfields to have struct layouts match MSVC, data types
are laid out in a struct with alignment according to their size.
However, this doesn't make sense for the long double type, since
it doesn't match MSVC at all, and aligning to a non-power-of-2
size triggers other asserts later.

This matches what GCC does, aligning a long double to 4 bytes
in structs on i386 even when -mms-bitfields is specified.

This fixes asserts when using the max_align_t data type when
building for MinGW/i386 with the -mms-bitfields flag.

Differential Revision: https://reviews.llvm.org/D43734

Modified:
    cfe/trunk/lib/AST/RecordLayoutBuilder.cpp
    cfe/trunk/test/CodeGen/mingw-long-double.c

Modified: cfe/trunk/lib/AST/RecordLayoutBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/RecordLayoutBuilder.cpp?rev=326173&r1=326172&r2=326173&view=diff
==============================================================================
--- cfe/trunk/lib/AST/RecordLayoutBuilder.cpp (original)
+++ cfe/trunk/lib/AST/RecordLayoutBuilder.cpp Mon Feb 26 22:27:06 2018
@@ -1752,7 +1752,12 @@ void ItaniumRecordLayoutBuilder::LayoutF
       QualType T = Context.getBaseElementType(D->getType());
       if (const BuiltinType *BTy = T->getAs<BuiltinType>()) {
         CharUnits TypeSize = Context.getTypeSizeInChars(BTy);
-        if (TypeSize > FieldAlign)
+        assert(
+            (llvm::isPowerOf2_64(TypeSize.getQuantity()) ||
+             Context.getTargetInfo().getTriple().isWindowsGNUEnvironment()) &&
+            "Non PowerOf2 size outside of GNU mode");
+        if (TypeSize > FieldAlign &&
+            llvm::isPowerOf2_64(TypeSize.getQuantity()))
           FieldAlign = TypeSize;
       }
     }

Modified: cfe/trunk/test/CodeGen/mingw-long-double.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/mingw-long-double.c?rev=326173&r1=326172&r2=326173&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/mingw-long-double.c (original)
+++ cfe/trunk/test/CodeGen/mingw-long-double.c Mon Feb 26 22:27:06 2018
@@ -1,5 +1,7 @@
 // RUN: %clang_cc1 -triple i686-windows-gnu -emit-llvm -o - %s \
 // RUN:    | FileCheck %s --check-prefix=GNU32
+// RUN: %clang_cc1 -triple i686-windows-gnu -emit-llvm -o - %s -mms-bitfields \
+// RUN:    | FileCheck %s --check-prefix=GNU32
 // RUN: %clang_cc1 -triple x86_64-windows-gnu -emit-llvm -o - %s \
 // RUN:    | FileCheck %s --check-prefix=GNU64
 // RUN: %clang_cc1 -triple x86_64-windows-msvc -emit-llvm -o - %s \