Store decls in prototypes on the declarator instead of in the AST

This saves two pointers from FunctionDecl that were being used for some
rare and questionable C-only functionality.  The DeclsInPrototypeScope
ArrayRef was added in r151712 in order to parse this kind of C code:

    enum e {x, y};
    int f(enum {y, x} n) {
     return x; // should return 1, not 0
    }

The challenge is that we parse 'int f(enum {y, x} n)' it its own
function prototype scope that gets popped before we build the
FunctionDecl for 'f'. The original change was doing two questionable
things:

1. Saving all tag decls introduced in prototype scope on a TU-global
Sema variable. This is problematic when you have cases like this, where
'x' and 'y' shouldn't be visible in 'f':
    void f(void (*fp)(enum { x, y } e)) { /* no x */ }
This patch fixes that, so now 'f' can't see 'x', which is consistent
with GCC.

2. Storing the decls in FunctionDecl in ActOnFunctionDeclarator so that
they could be used in ActOnStartOfFunctionDef. This is just an
inefficient way to move information around. The AST lives forever, but
the list of non-parameter decls in prototype scope is short lived.

Moving these things to the Declarator solves both of these issues.

Reviewers: rsmith

Subscribers: jmolloy, cfe-commits

Differential Revision: https://reviews.llvm.org/D27279

llvm-svn: 289225

1 files changed, 16 insertions, 0 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index ea7ab267701..9dda75e3f98 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -5827,6 +5827,21 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
     }
   }
 
+  // Collect non-parameter declarations from the prototype if this is a function
+  // declaration. They will be moved into the scope of the function. Only do
+  // this in C and not C++, where the decls will continue to live in the
+  // surrounding context.
+  SmallVector<NamedDecl *, 0> DeclsInPrototype;
+  if (getCurScope()->getFlags() & Scope::FunctionDeclarationScope &&
+      !getLangOpts().CPlusPlus) {
+    for (Decl *D : getCurScope()->decls()) {
+      NamedDecl *ND = dyn_cast<NamedDecl>(D);
+      if (!ND || isa<ParmVarDecl>(ND))
+        continue;
+      DeclsInPrototype.push_back(ND);
+    }
+  }
+
   // Remember that we parsed a function type, and remember the attributes.
   D.AddTypeInfo(DeclaratorChunk::getFunction(HasProto,
                                              IsAmbiguous,
@@ -5846,6 +5861,7 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
                                              NoexceptExpr.isUsable() ?
                                                NoexceptExpr.get() : nullptr,
                                              ExceptionSpecTokens,
+                                             DeclsInPrototype,
                                              StartLoc, LocalEndLoc, D,
                                              TrailingReturnType),
                 FnAttrs, EndLoc);