Re: Patch: performing decl operation on type

[Robert Bowdidge <bowdidge at apple dot com>]

In cp_finish_decl() (gcc/cp/decl.c:7837, top of tree code), the 
following code appears:

  if (TREE_CODE (decl) == FIELD_DECL && asmspec)
    {
      /* This must override the asm specifier which was placed by
         grokclassfn.  Lay this out fresh.  */
      SET_DECL_RTL (TREE_TYPE (decl), NULL_RTX);


This code is suspicious -- it's one of very few places in the C and C++ 
front ends where the contents of the type field are manipulated in a 
non-type way.    The code, in one form or another, dates from at least 
the beginning of Cygnus's RCS server in 1992.  I suspect that the the 
SET_DECL_RTL was supposed to act on decl, not on TREE_TYPE(decl), and 
the TREE_TYPE() was added incorrectly.   None of the other occurrences 
I found manipulated declarations in the type field; the other offenders 
were storing line numbers in the type field (config/rs6000/rs6000.c) 
and lists (in the Objective C front end).

This code also must never be run, for the type check in SET_DECL_RTL 
would have put out an assertion if so.  With a test case that should 
trigger this code, the offending code was never actually called:

struct foo {
  static int bar __asm__ ("barbaz");
}
main() {
  printf("Hello world!\n");
}

Specifically, static variable declarations in a structure get converted 
from FIELD_DECL to VAR_DECL before this point.  Non-static variables in 
a structure cannot have asm directives in C++; the warning happens 
before cp_finish_decl, and thus also never hit this code.

I'd like to remove this code because it's (1) dead code and (2) shows a 
misleading use of the macros and data structures.  With this code 
removed, dejagnu shows no regressions.  I've also added g++ test cases 
to check that  asmspecs on structure fields generate an error, and that 
asmspecs on static structure fields correctly generates a binary 
referencing these symbols.

This code was found as part of a quick-and-dirty test to see if making 
typing stricter was possible.

Ok to submit?

Robert Bowdidge



diff -u -b -d -r1.1139 decl.c
--- cp/decl.c   3 Oct 2003 20:27:04 -0000       1.1139
+++ cp/decl.c   10 Oct 2003 23:41:35 -0000
@@ -7834,7 +7834,7 @@
     {
       /* This must override the asm specifier which was placed by
         grokclassfn.  Lay this out fresh.  */
-      SET_DECL_RTL (TREE_TYPE (decl), NULL_RTX);
+      SET_DECL_RTL (decl, NULL_RTX);
       SET_DECL_ASSEMBLER_NAME (decl, get_identifier (asmspec));
       make_decl_rtl (decl, asmspec);
     }


ChangeLog:
        * cp/decl.c (cp_finish_decl):  Remove clause intended for asm 
directives in struct or class fields: this code is never executed.

Added test cases:

gcc/testsuite/g++.dg/ext/asmspecValid.C:

// tests that the asm directive is correctly handled for static fields
// in structures and classes.  This only applies to C++; such
// directives generate errors in C.  Assembler directives for local
// variables should be tested by the C test suite.
//
// Contributed by Robert Bowdidge (bowdidge@apple.com) 14 Oct 2003

// { dg-do compile }

struct Foo {
  // This should reference a variable called bar
  static int i __asm__("bar");
};


class Bar {
public:
  static int i __asm__("theRealI");
  static int j __asm__("theRealJ");
  int boof;
};

class Baz : public Bar {
public:
   static char *ptr __asm__ ("theRealString");
};

int main (int argc, char **argv) {
  struct Foo myFoo;
  Bar b;
  myFoo.i = 1;
  Foo::i = 2;
  Baz::j = 10;
  Baz::ptr = 0;
  b.i = 1;
  return (b.i);
}


/* { dg-final {scan-assembler "bar"} } */
/* { dg-final {scan-assembler "theRealString"} } */
/* { dg-final {scan-assembler "theRealI" } } */
/* { dg-final {scan-assembler "theRealJ" } } */



gcc/testsuite/g++.dg/ext/asmspecInvalid.C:

// tests that the asm directive is correctly handled for static fields
// in structures and classes.  This only applies to C++; such
// directives generate errors in C.  Assembler directives for local
// variables should be tested by the C test suite.
//
// Contributed by Robert Bowdidge (bowdidge@apple.com) 14 Oct 2003

// { dg-do compile }

struct Foo {
  // This should reference a variable called bar
  int i __asm__("bar");  /* { dg-error "specifiers are not permitted" } 
*/
};

int main (void ) {
  int j = 0;
  return j;
}