[Bug c++/59739] New: missed optimization: attribute ((pure)) could be honored more often

["joerg.richter@pdv-fs.de" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59739

            Bug ID: 59739
           Summary: missed optimization: attribute ((pure)) could be
                    honored more often
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: joerg.richter@pdv-fs.de

Created attachment 31786
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31786&action=edit
Script for demonstration

Attached is a script (t.sh) that creates two .cc files, compiles and executes
them.

It tests whether attribute ((pure)) is used on different functions with this
signatures:

struct Struct { int val; };
int globalInt();
Struct globalStruct();
struct Class {
  int classInt();
  Struct classStruct();
  virtual int classVirtualInt();
  virtual Struct classVirtualStruct();
};

The output with GCC is 4.8.2 is this:

globalInt: 1
globalStruct: 0
classInt: 1
classStruct: 0
classVirtualInt: 0
classVirtualStruct: 0

Meaning only globalInt and classInt are optimised.

All other functions are also candidates for attribute-pure optimisation.