Hi Christophe,
I'm testing the attached patch, but without an aarch64, it'll take a while to
figure
out the toolchain to reproduce the failure. Neither of the platforms I tested
were
affected, but I can see it's unsafe to reuse the subreg_promoted_reg idiom from
just a few lines earlier. Any help testing the attached patch on an affected
target
would be much appreciated.
Sorry for the inconvenience.
Roger
--
-----Original Message-----
From: Christophe LYON <christophe.l...@foss.st.com>
Sent: 31 August 2021 13:32
To: Roger Sayle <ro...@nextmovesoftware.com>; 'GCC Patches'
<gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Preserve SUBREG_PROMOTED_VAR_P on (extend:HI (subreg/s:QI
(reg:SI)))
On 29/08/2021 09:46, Roger Sayle wrote:
> SUBREG_PROMOTED_VAR_P is a mechanism for tracking that a partial
> subreg is correctly zero-extended or sign-extended in the parent
> register. For example, the RTL (subreg/s/v:QI (reg/v:SI 23 [ x ]) 0)
> indicates that the byte x is zero extended in reg:SI 23, which is useful for
> optimization.
> An example is that zero extending the above QImode value to HImode can
> simply use a wider subreg, i.e. (subreg:HI (reg/v:SI 23 [ x ]) 0).
>
> This patch addresses the oversight/missed optimization opportunity
> that the new HImode subreg above should retain its
> SUBREG_PROMOTED_VAR_P annotation as its value is guaranteed to be
> correctly extended in the SImode parent. The code below to preserve
> SUBREG_PROMOTED_VAR_P is already present in the middle-end (e.g.
> simplify-rtx.c:7232-7242) but missing from one or two (precisely three)
> places that (accidentally) strip it.
>
> Whilst there I also added another optimization. If we need to extend
> the above QImode value beyond the SImode register holding it, say to
> DImode, we can eliminate the SUBREG and simply extend from the SImode
> register to DImode.
>
> This patch has been tested on x86_64-pc-linux-gnu with "make bootstrap"
> and "make -k check" with no new failures, and on a cross-compiler to
> nvptx-none, where the function "long foo(char x) { return x; }" now
> requires one less instruction.
>
> OK for mainline?
Hi,
This patch causes an ICE when building an aarch64 toolchain:
during RTL pass: expand
In file included from
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libgcc/soft-fp/soft-fp.h:318,
from
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libgcc/soft-fp/floatditf.c:32:
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libgcc/soft-fp/floatditf.c:
In function '__floatditf':
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libgcc/soft-fp/op-2.h:249:37:
internal compiler error: in subreg_promoted_mode, at rtl.h:3132
249 | _FP_PACK_RAW_2_flo.bits.exp = X##_e; \
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libgcc/soft-fp/quad.h:229:33:
note: in expansion of macro '_FP_PACK_RAW_2'
229 | # define FP_PACK_RAW_Q(val, X) _FP_PACK_RAW_2 (Q, (val), X)
| ^~~~~~~~~~~~~~
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/libgcc/soft-fp/floatditf.c:42:3:
note: in expansion of macro 'FP_PACK_RAW_Q'
42 | FP_PACK_RAW_Q (a, A);
| ^~~~~~~~~~~~~
0xa0b53a subreg_promoted_mode
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/rtl.h:3132
0xa0b53a convert_modes(machine_mode, machine_mode, rtx_def*, int)
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:699
0xa003bc expand_expr_real_2(separate_ops*, rtx_def*, machine_mode,
expand_modifier)
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:9091
0xa0765c expand_expr_real_1(tree_node*, rtx_def*, machine_mode,
expand_modifier, rtx_def**, bool)
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:10497
0x9fcef6 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode,
expand_modifier)
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:9798
0xa0765c expand_expr_real_1(tree_node*, rtx_def*, machine_mode,
expand_modifier, rtx_def**, bool)
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:10497
0xa1099e expand_expr
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.h:301
0xa1099e expand_operands(tree_node*, tree_node*, rtx_def*, rtx_def**,
rtx_def**, expand_modifier)
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:8308
0x9fcdff expand_expr_real_2(separate_ops*, rtx_def*, machine_mode,
expand_modifier)
/tmp/5987050_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/expr.c:10288
Can you check?
Thanks,
Christophe
>
> 2021-08-29 Roger Sayle <ro...@nextmovesoftware.com>
>
> gcc/ChangeLog
> * expr.c (convert_modes): Preserve SUBREG_PROMOTED_VAR_P when
> creating a (wider) partial subreg from a SUBREG_PROMOTED_VAR_P
> subreg.
> * simplify-rtx.c (simplify_unary_operation_1) [SIGN_EXTEND]:
> Likewise, preserve SUBREG_PROMOTED_VAR_P when creating a (wider)
> partial subreg from a SUBREG_PROMOTED_VAR_P subreg. Generate
> SIGN_EXTEND of the SUBREG_REG when a subreg would be paradoxical.
> [ZERO_EXTEND]: Likewise, preserve SUBREG_PROMOTED_VAR_P when
> creating a (wider) partial subreg from a SUBREG_PROMOTED_VAR_P
> subreg. Generate ZERO_EXTEND of the SUBREG_REG when a subreg
> would be paradoxical.
>
> Roger
> --
>
diff --git a/gcc/expr.c b/gcc/expr.c
index 5dd98a9..17f2c2f 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -690,17 +690,20 @@ convert_modes (machine_mode mode, machine_mode oldmode,
rtx x, int unsignedp)
&& SUBREG_CHECK_PROMOTED_SIGN (x, unsignedp))
{
scalar_int_mode int_orig_mode;
+ scalar_int_mode int_inner_mode;
machine_mode orig_mode = GET_MODE (x);
x = gen_lowpart (int_mode, SUBREG_REG (x));
/* Preserve SUBREG_PROMOTED_VAR_P if the new mode is wider than
the original mode, but narrower than the inner mode. */
if (GET_CODE (x) == SUBREG
- && GET_MODE_PRECISION (subreg_promoted_mode (x))
- > GET_MODE_PRECISION (int_mode)
&& is_a <scalar_int_mode> (orig_mode, &int_orig_mode)
&& GET_MODE_PRECISION (int_mode)
- > GET_MODE_PRECISION (int_orig_mode))
+ > GET_MODE_PRECISION (int_orig_mode)
+ && is_a <scalar_int_mode> (GET_MODE (SUBREG_REG (x)),
+ &int_inner_mode)
+ && GET_MODE_PRECISION (int_inner_mode)
+ > GET_MODE_PRECISION (int_mode))
{
SUBREG_PROMOTED_VAR_P (x) = 1;
SUBREG_PROMOTED_SET (x, unsignedp);
