Re: [PATCH V1] HIGH part of symbol ref is invalid for constant pool

[Segher Boessenkool <segher@kernel.crashing.org>]

Hi!

On Tue, Jul 19, 2022 at 10:30:54PM +0800, Jiufu Guo wrote:
> In patch https://gcc.gnu.org/pipermail/gcc-patches/2022-July/597712.html,
> test case was not added.  After more check, a testcase is added for it.
> 
> The high part of the symbol address is invalid for the constant pool.

Invalid, how so?  Is there a PR related here?

But it is not particularly useful ever, either: we do not know two
different addresses will have the same HIGH unless we know the exact
address, and then we don't need HIGH anyway.

> 	* config/rs6000/rs6000.cc (rs6000_cannot_force_const_mem):
> 	Return true for HIGH code rtx.

	* config/rs6000/rs6000.cc (rs6000_cannot_force_const_mem): Return true
	for HIGH code rtx.

Please don't wrap lines early: changelog lines are 80 positions long,
including the leading tab (which counts as eight positions).

>  static bool
>  rs6000_cannot_force_const_mem (machine_mode mode ATTRIBUTE_UNUSED, rtx x)
>  {
> -  if (GET_CODE (x) == HIGH
> -      && GET_CODE (XEXP (x, 0)) == UNSPEC)
> +  /* High part of a symbol ref/address can not be put into constant pool. e.g.
> +     (high:DI (symbol_ref:DI ("var")..)) or
> +     (high:DI (unspec:DI [(symbol_ref/u:DI ("*.LC0")..)
> +     (high:DI (const:DI (plus:DI (symbol_ref:DI ("xx")) (const_int 12)))).  */
> +  if (GET_CODE (x) == HIGH)
>      return true;

I'm not sure the new comment is helpful at all?  Are these examples of
where the compiler (or assembler perhaps) will choke?

> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/constpoolcheck.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile { target powerpc*-*-* } } */

Everything in gcc.target/powerpc is target powerpc* always.

> +/* { dg-options "-O1 -mdejagnu-cpu=power10" } */
> +/* (high:DI (symbol_ref:DI ("var_48")..))) should not cause ICE. */

Ah, so there is an ICE, I see.  Please open a PR, and mention that in
the testcase as well as in the commit message and changelog.

I agree with what the patch does, it just needs a little more work :-)


Segher