Re: Is there really only one symbol_ref object referring to eachsymbolic label?

[Kazu Hirata <kazu at cs dot umass dot edu>]

Hi Geoff,

> > GCC Internals Manual states that
> > 
> >   For any symbolic label, there is only one symbol_ref object
> >   referring to it.
> > 
> > Does this mean x == y iff XSTR (x, 0) == XSTR (y, 0), assuming both x
> > and y are SYMBOL_REF?  If so, looking at gen_rtx_SYMBOL_REF, I think
> > we can get two different rtx objects just by saying
> > 
> >   x = gen_rtx_SYMBOL_REF (Pmode, "hello");
> >   y = gen_rtx_SYMBOL_REF (Pmode, strdup ("hello"));
> > 
> > Or are we not supposed to do this?
> 
> Strings in SYMBOL_REFs are supposed to live in the identifier hash
> table, and so should be unique...

I see.  Then I guess it could potentially be dangerous to have
multiple places creating the same SYMBOL_REFs like

sh/sh.md:8059:  operands[2] = gen_rtx_SYMBOL_REF (SImode, \"__fpscr_values\");
sh/sh.md:8073:  operands[2] = gen_rtx_SYMBOL_REF (SImode, \"__fpscr_values\");

and

sparc/sparc.md:1937:  operands[2] = gen_rtx_SYMBOL_REF (Pmode, "_GLOBAL_OFFSET_TABLE_");
sparc/sparc.md:2178:  operands[2] = gen_rtx_SYMBOL_REF (Pmode, "_GLOBAL_OFFSET_TABLE_");
x

because rtx_equal_p and a *lot* of its variants use

  XSTR (x, 0) == XSTR (y, 0)

to compare two SYMBOL_REFs.  If the host compiler assigns two
identical string constants two different addresses, the comparison may
fail.

Kazu Hirata