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Re: [PATCH] Set TREE_READONLY const POD arrays with sizedetermined from initialize (PR c++/21454)

> From: Jakub Jelinek <>
> On Wed, May 11, 2005 at 06:37:53PM -0400, Paul Schlie wrote:
>>> Jakub Jelinek <> writes:
>>> This is a fallout of the PR c++/20073 fix.
>>> For arrays like:
>>> const int a[] = { 0, 1, 2, 3 };
>>> when cp_apply_type_quals_to_decl is called, its type is not complete yet,
>>> so C++ frontend does not set TREE_READONLY flag.  But such variables
>>> aren't put into incomplete_vars chain either, so nothing sets the flag
>>> afterwards.
>>> Ok for 4.0/HEAD if it passes regtesting?
>> What's the difference between TREE_READONLY and MEM_READONLY_P ?
> TREE_READONLY is a tree flag, MEM_READONLY_P is a rtl flag.
> They both mean basically the same thing, that the object is not modified
> once the program gets control (i.e. e.g. variables in read-only sections are
> ok,

- Yup, makes sense.

>    variables in writable sections that are there just because they need to
> be relocated by the dynamic linker (which is even before constructors are
> run) and are never modified afterwards are ok too.

- Just to double check, as dynamically allocated variables can never be
  designated READONLY; I presume you mean that such variables may be
  initialized with read-only literal data (which is distinct from the
  variables themselves, not a relocation), as opposed to READONLY variables
  and/or literals, which are equivalent to their initializing data. i.e.:

  char foo (int x, int y)
    char s[3] = "abc";
    s[x] = 'x';
    return s[y];

  where "abc" (a READONLY literal char array) initializes by being copied
  to s[] (a non-READONLY variable char array) upon entry to foo, vs.

  static const char s[3] = "abc";
  where s[] is equivalent to the literal "abc" and are one and the same.

>> (To the best of my knowledge "const int a[]" is allocated and initialized
>>  at run-time in RAM with the READONLY ROM literal value "{1,2,3,4}"; so a[]
>>  is not READONLY, although it's literal initializer is; as opposed to
>>  "static const a[] = {0,1,2,3}" where they are considered equivalent.)
> No, there is no difference outside of function body whether there is
> static keyword or not.

OK that makes sense, as static is essentially presumed; however within a
function body, I presume only "static const" variables (and literal data),
may be classified as being READONLY?

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