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
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