On Mon, 12 Apr 2021, Jakub Jelinek wrote:
> Hi!
>
> Similarly to PR95450 done on GIMPLE, this patch punts if we try to
> simplify_{gen_,}subreg from some constant into the IBM double double
> IFmode (or sometimes TFmode) if the double double format wouldn't preserve
> the bits. Not all values are valid in IBM double double, e.g. the format
> requires that the upper double is the whole value rounded to double, and
> if in some cases such as in the pr71522.c testcase with -m32 -Os -mcpu=power7
> some non-floating data is copied through long double variable, we can
> simplify a subreg into something that has different value.
>
> Fixed by punting if the planned simplify_immed_subreg result doesn't
> encode to bitwise identical values compared to what we were decoding.
>
> As for the simplify_gen_subreg change, I think it would be desirable
> to just avoid creating SUBREGs of constants on all targets and for all
> constants, if simplify_immed_subreg simplified, fine, otherwise punt,
> but as we are late in GCC11 development, the patch instead guards this
> behavior on MODE_COMPOSITE_P (outermode) - i.e. only conversions to
> powerpc{,64,64le} double double long double - and only for the cases where
> simplify_immed_subreg was called.
>
> Bootstrapped/regtested on powerpc64{,le}-linux, on powerpc64-linux tested
> with -m32/-m64, ok for trunk?
OK.
Richard.
> 2021-04-12 Jakub Jelinek <ja...@redhat.com>
>
> PR target/99648
> * simplify-rtx.c (simplify_immed_subreg): For MODE_COMPOSITE_P
> outermode, return NULL if the result doesn't encode back to the
> original byte sequence.
> (simplify_gen_subreg): Don't create SUBREGs from constants to
> MODE_COMPOSITE_P outermode.
>
> --- gcc/simplify-rtx.c.jj 2021-04-10 12:45:22.189863341 +0200
> +++ gcc/simplify-rtx.c 2021-04-12 12:06:01.469088000 +0200
> @@ -7035,12 +7035,19 @@ simplify_immed_subreg (fixed_size_mode o
> while (buffer.length () < buffer_bytes)
> buffer.quick_push (filler);
> }
> - else
> + else if (!native_encode_rtx (innermode, x, buffer, first_byte,
> inner_bytes))
> + return NULL_RTX;
> + rtx ret = native_decode_rtx (outermode, buffer, 0);
> + if (ret && MODE_COMPOSITE_P (outermode))
> {
> - if (!native_encode_rtx (innermode, x, buffer, first_byte, inner_bytes))
> + auto_vec<target_unit, 128> buffer2 (buffer_bytes);
> + if (!native_encode_rtx (outermode, ret, buffer2, 0, buffer_bytes))
> return NULL_RTX;
> - }
> - return native_decode_rtx (outermode, buffer, 0);
> + for (unsigned int i = 0; i < buffer_bytes; ++i)
> + if (buffer[i] != buffer2[i])
> + return NULL_RTX;
> + }
> + return ret;
> }
>
> /* Simplify SUBREG:OUTERMODE(OP:INNERMODE, BYTE)
> @@ -7336,6 +7343,13 @@ simplify_context::simplify_gen_subreg (m
> || GET_MODE (op) == VOIDmode)
> return NULL_RTX;
>
> + if (MODE_COMPOSITE_P (outermode)
> + && (CONST_SCALAR_INT_P (op)
> + || CONST_DOUBLE_AS_FLOAT_P (op)
> + || CONST_FIXED_P (op)
> + || GET_CODE (op) == CONST_VECTOR))
> + return NULL_RTX;
> +
> if (validate_subreg (outermode, innermode, op, byte))
> return gen_rtx_SUBREG (outermode, op, byte);
>
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
