From: Martin Storsjo <martin@martin.st>
Date: Tue, 27 Feb 2018 06:27:06 +0000 (+0000)
Subject: [RecordLayout] Don't align to non-power-of-2 sizes when using -mms-bitfields
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=9601b191822ef80f037b0d2ed31491f9392b8d9b;p=clang

[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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@326173 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/AST/RecordLayoutBuilder.cpp b/lib/AST/RecordLayoutBuilder.cpp
index dddacf2a5f..a882c5ee9f 100644
--- a/lib/AST/RecordLayoutBuilder.cpp
+++ b/lib/AST/RecordLayoutBuilder.cpp
@@ -1752,7 +1752,12 @@ void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
       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;
       }
     }
diff --git a/test/CodeGen/mingw-long-double.c b/test/CodeGen/mingw-long-double.c
index d1e3a62079..d344d9f5a1 100644
--- a/test/CodeGen/mingw-long-double.c
+++ b/test/CodeGen/mingw-long-double.c
@@ -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 \