RFA: Fix ICE on PARALLEL returns when expand builtins

[Richard Biener]

On Sun, Dec 23, 2012 at 10:43 AM, Richard Sandiford
<rdsandiford@googlemail.com> wrote:
> Some of the maths builtins can expand to a call followed by a bit
> of postprocessing.  With 4.8's PARALLEL return optimisations, these
> embedded calls might return a PARALLEL of pseudos, but the postprocessing
> isn't prepared to deal with that.  This leads to an ICE in builtins-53.c
> on n32 and n64 mips64-linux-gnu.
>
> One fix might have been to pass an explicit register target to the
> expand routines, but that target's only a hint.  This patch instead
> adds an avoid_group_rtx function (named after gen_group_rtx) to convert
> PARALLELs to pseudos where necessary.
>
> I wondered whether it was really safe for expand_builtin_int_roundingfn_2
> to pass "target == const0_rtx" as the "ignore" parameter to expand_call,
> given that we don't actually ignore the return value ourselves
> (even if the caller does).  I suppose it is safe though,
> since expand_call will always return const0_rtx in that case,
> and this code is dealing with integer return values.
>
> Tested on mips64-linux-gnu.  OK to install?  Or is there a better way?

You didn't add a testcase so I can't check myself - but why isn't
using force_reg enough here?  I can imagine other cases than PARALLELs
that are not well handled, no?

Thanks,
Richard.

> Richard
>
>
> gcc/
>         * expr.h (avoid_group_rtx): Declare.
>         * expr.c (avoid_group_rtx): New function.
>         * builtins.c (expand_builtin_int_roundingfn): Call it.
>         (expand_builtin_int_roundingfn_2): Likewise.
>
> Index: gcc/expr.h
> ===================================================================
> --- gcc/expr.h  2012-12-23 09:21:21.969086853 +0000
> +++ gcc/expr.h  2012-12-23 09:32:03.487440220 +0000
> @@ -334,6 +334,8 @@ extern rtx emit_group_move_into_temps (r
>     PARALLEL.  */
>  extern void emit_group_store (rtx, rtx, tree, int);
>
> +extern rtx avoid_group_rtx (rtx, tree);
> +
>  /* Copy BLKmode object from a set of registers.  */
>  extern void copy_blkmode_from_reg (rtx, rtx, tree);
>
> Index: gcc/expr.c
> ===================================================================
> --- gcc/expr.c  2012-12-23 09:21:21.980086911 +0000
> +++ gcc/expr.c  2012-12-23 09:32:03.485440208 +0000
> @@ -2079,6 +2079,23 @@ emit_group_store (rtx orig_dst, rtx src,
>      emit_move_insn (orig_dst, dst);
>  }
>
> +/* Return a form of X that does not use a PARALLEL.  TYPE is the type
> +   of the value stored in X.  */
> +
> +rtx
> +avoid_group_rtx (rtx x, tree type)
> +{
> +  enum machine_mode mode = TYPE_MODE (type);
> +  gcc_checking_assert (GET_MODE (x) == VOIDmode || GET_MODE (x) == mode);
> +  if (GET_CODE (x) == PARALLEL)
> +    {
> +      rtx result = gen_reg_rtx (mode);
> +      emit_group_store (result, x, type, int_size_in_bytes (type));
> +      return result;
> +    }
> +  return x;
> +}
> +
>  /* Copy a BLKmode object of TYPE out of a register SRCREG into TARGET.
>
>     This is used on targets that return BLKmode values in registers.  */
> Index: gcc/builtins.c
> ===================================================================
> --- gcc/builtins.c      2012-12-23 09:21:21.981086916 +0000
> +++ gcc/builtins.c      2012-12-23 09:34:47.813323158 +0000
> @@ -2757,6 +2757,7 @@ expand_builtin_int_roundingfn (tree exp,
>    exp = build_call_nofold_loc (EXPR_LOCATION (exp), fallback_fndecl, 1, arg);
>
>    tmp = expand_normal (exp);
> +  tmp = avoid_group_rtx (tmp, TREE_TYPE (exp));
>
>    /* Truncate the result of floating point optab to integer
>       via expand_fix ().  */
> @@ -2860,6 +2861,7 @@ expand_builtin_int_roundingfn_2 (tree ex
>                                    fallback_fndecl, 1, arg);
>
>        target = expand_call (exp, NULL_RTX, target == const0_rtx);
> +      target = avoid_group_rtx (target, TREE_TYPE (exp));
>        return convert_to_mode (mode, target, 0);
>      }
>