mstorsjo created this revision.
mstorsjo added reviewers: rsmith, rjmccall, rnk, Mordante.
Herald added a project: clang.
GCC 7 and earlier, when targeting MinGW, seems to have a bug in layout/size of
bitfield structs if they contain a nested enum, making the size of the struct 8
bytes, while we have a static assert requiring it to be 4 bytes or less.
While this clearly is a GCC bug, the workaround (moving the enum out of the
bitfield) also is very nonintrusive and matches other existing enums there.
Testcase:
$ cat bitfield.cpp
struct MyStruct {
unsigned a : 1;
enum { SomeValue = 42 };
unsigned b : 1;
};
int StructSize = sizeof(struct MyStruct);
$ x86_64-w64-mingw32-g++ -S -o - bitfield.cpp | grep -C 2 StructSize
.file "bitfield.cpp"
.text
.globl StructSize
.data
.align 4
StructSize:
.long 8
.ident "GCC: (GNU) 7.3-win32 20180312"
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D71650
Files:
clang/include/clang/AST/Decl.h
Index: clang/include/clang/AST/Decl.h
===================================================================
--- clang/include/clang/AST/Decl.h
+++ clang/include/clang/AST/Decl.h
@@ -900,6 +900,8 @@
DAK_Normal
};
+ enum { NumScopeDepthOrObjCQualsBits = 7 };
+
class ParmVarDeclBitfields {
friend class ASTDeclReader;
friend class ParmVarDecl;
@@ -922,8 +924,6 @@
/// Whether this parameter is an ObjC method parameter or not.
unsigned IsObjCMethodParam : 1;
- enum { NumScopeDepthOrObjCQualsBits = 7 };
-
/// If IsObjCMethodParam, a Decl::ObjCDeclQualifier.
/// Otherwise, the number of function parameter scopes enclosing
/// the function parameter scope in which this parameter was
@@ -1654,7 +1654,7 @@
}
static constexpr unsigned getMaxFunctionScopeDepth() {
- return (1u << ParmVarDeclBitfields::NumScopeDepthOrObjCQualsBits) - 1;
+ return (1u << NumScopeDepthOrObjCQualsBits) - 1;
}
/// Returns the index of this parameter in its prototype or method scope.
Index: clang/include/clang/AST/Decl.h
===================================================================
--- clang/include/clang/AST/Decl.h
+++ clang/include/clang/AST/Decl.h
@@ -900,6 +900,8 @@
DAK_Normal
};
+ enum { NumScopeDepthOrObjCQualsBits = 7 };
+
class ParmVarDeclBitfields {
friend class ASTDeclReader;
friend class ParmVarDecl;
@@ -922,8 +924,6 @@
/// Whether this parameter is an ObjC method parameter or not.
unsigned IsObjCMethodParam : 1;
- enum { NumScopeDepthOrObjCQualsBits = 7 };
-
/// If IsObjCMethodParam, a Decl::ObjCDeclQualifier.
/// Otherwise, the number of function parameter scopes enclosing
/// the function parameter scope in which this parameter was
@@ -1654,7 +1654,7 @@
}
static constexpr unsigned getMaxFunctionScopeDepth() {
- return (1u << ParmVarDeclBitfields::NumScopeDepthOrObjCQualsBits) - 1;
+ return (1u << NumScopeDepthOrObjCQualsBits) - 1;
}
/// Returns the index of this parameter in its prototype or method scope.
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