Missing qualifiers in derived to base implicit casts

[Abramo Bagnara]

(filed as https://llvm.org/bugs/show_bug.cgi?id=23409, sent to list by
Richard request)

The typescript below shows that the UncheckedDerivedToBase implicit cast
destination type is not const qualified as it should.

I've attached a patch to fix that for review.

$ cat p.cc
struct b {
  int x;
};

struct d : b {
};

void f() {
  const d* p;
  int v = p->x;
}
$ clang++ -cc1 -ast-dump p.cc
TranslationUnitDecl 0x1aff920 <<invalid sloc>> <invalid sloc>
|-TypedefDecl 0x1affe60 <<invalid sloc>> <invalid sloc> implicit
__int128_t '__int128'
|-TypedefDecl 0x1affec0 <<invalid sloc>> <invalid sloc> implicit
__uint128_t 'unsigned __int128'
|-TypedefDecl 0x1b00280 <<invalid sloc>> <invalid sloc> implicit
__builtin_va_list '__va_list_tag [1]'
|-CXXRecordDecl 0x1b002d0 <p.cc:1:1, line:3:1> line:1:8 struct b definition
| |-CXXRecordDecl 0x1b003e0 <col:1, col:8> col:8 implicit struct b
| `-FieldDecl 0x1b00480 <line:2:3, col:7> col:7 referenced x 'int'
|-CXXRecordDecl 0x1b004d0 <line:5:1, line:6:1> line:5:8 struct d definition
| |-public 'struct b'
| `-CXXRecordDecl 0x1b431f0 <col:1, col:8> col:8 implicit struct d
`-FunctionDecl 0x1b432d0 <line:8:1, line:11:1> line:8:6 f 'void (void)'
  `-CompoundStmt 0x1b43578 <col:10, line:11:1>
    |-DeclStmt 0x1b43408 <line:9:3, col:13>
    | `-VarDecl 0x1b433b0 <col:3, col:12> col:12 used p 'const struct d *'
    `-DeclStmt 0x1b43560 <line:10:3, col:15>
      `-VarDecl 0x1b43430 <col:3, col:14> col:7 v 'int' cinit
        `-ImplicitCastExpr 0x1b43548 <col:11, col:14> 'int' <LValueToRValue>
          `-MemberExpr 0x1b43518 <col:11, col:14> 'const int' lvalue ->x
0x1b00480
            `-ImplicitCastExpr 0x1b434f8 <col:11> 'struct b *'
<UncheckedDerivedToBase (b)>
              `-ImplicitCastExpr 0x1b434b0 <col:11> 'const struct d *'
<LValueToRValue>
                `-DeclRefExpr 0x1b43488 <col:11> 'const struct d *'
lvalue Var 0x1b433b0 'p' 'const struct d *'

-- 
Abramo Bagnara

BUGSENG srl - http://bugseng.com
mailto:abramo.bagnara at bugseng.com
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