Implement #pragma pack use in structure packing. The general approach
is to encode the state of the #pragma pack stack as an attribute when
the structure is declared.
- Extend PackedAttr to take an alignment (in bits), and reuse for
both __attribute__((packed)) (which takes no argument, instead
packing tightly (to "minimize the memory required") and for #pragma
pack (which allows specification of the maximum alignment in
bytes). __attribute__((packed)) is just encoded as Alignment=1.
This conflates two related but different mechanisms, but it didn't
seem worth another attribute.
- I have attempted to follow the MSVC semantics as opposed to the gcc
ones, since if I understand correctly #pragma pack originated with
MSVC. The semantics are generally equivalent except when the stack
is altered during the definition of a structure; its not clear if
anyone does this in practice. See testcase if curious.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@57623 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index fee732f..e32da24 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -1939,6 +1939,20 @@
// Add it to the decl chain.
PushOnScopeChains(New, S);
}
+
+ // Handle #pragma pack: if the #pragma pack stack has non-default
+ // alignment, make up a packed attribute for this decl. These
+ // attributes are checked when the ASTContext lays out the
+ // structure.
+ //
+ // It is important for implementing the correct semantics that this
+ // happen here (in act on tag decl). The #pragma pack stack is
+ // maintained as a result of parser callbacks which can occur at
+ // many points during the parsing of a struct declaration (because
+ // the #pragma tokens are effectively skipped over during the
+ // parsing of the struct).
+ if (unsigned Alignment = PackContext.getAlignment())
+ New->addAttr(new PackedAttr(Alignment * 8));
if (Attr)
ProcessDeclAttributeList(New, Attr);