diff mbox series

Preserve SUBREG_PROMOTED_VAR_P on (extend:HI (subreg/s:QI (reg:SI)))

Message ID 02d101d79ca9$eaa16210$bfe42630$@nextmovesoftware.com
State New
Headers show
Series Preserve SUBREG_PROMOTED_VAR_P on (extend:HI (subreg/s:QI (reg:SI))) | expand

Commit Message

Roger Sayle Aug. 29, 2021, 7:46 a.m. UTC 
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?


2021-08-29  Roger Sayle  <roger@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
--

Comments

Jeff Law Aug. 29, 2021, 8:59 p.m. UTC | #1 
On 8/29/2021 1:46 AM, 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?
>
>
> 2021-08-29  Roger Sayle  <roger@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.
OK
jeff
Christophe Lyon Aug. 31, 2021, 12:32 p.m. UTC | #2 
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  <roger@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
> --
>
Roger Sayle Aug. 31, 2021, 1:24 p.m. UTC | #3 
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.lyon@foss.st.com> 
Sent: 31 August 2021 13:32
To: Roger Sayle <roger@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  <roger@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);
Jeff Law Aug. 31, 2021, 3:30 p.m. UTC | #4 
On 8/31/2021 7:24 AM, Roger Sayle wrote:
> 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.lyon@foss.st.com>
> Sent: 31 August 2021 13:32
> To: Roger Sayle <roger@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  <roger@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
>> --
>>
>>
>> patch.txt
>>
>> diff --git a/gcc/expr.c b/gcc/expr.c
>> index 5dd98a9..17f2c2f 100644
>> --- a/gcc/expr.c
>> +++ b/gcc/expr.c
This seems to be fixing the failures spotted by my tester.  iq2000, 
fr30, cris, epiphany so far.  I suspect it'll fix the others as well.

jeff
Rainer Orth Aug. 31, 2021, 9 p.m. UTC | #5 
Hi Roger,

> 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.

after reverting the patch that caused PR middle-end/102133 and had
already broken 32-bit sparc bootstrap, sparc was affected again by this
one for a couple of files in 64-bit libgcc.

Fortunately, this patch fixes the build (only tried a minimal
non-bootstrap so far).

	Rainer
diff mbox series

Patch

diff --git a/gcc/expr.c b/gcc/expr.c
index 096c031..5dd98a9 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -688,7 +688,24 @@  convert_modes (machine_mode mode, machine_mode oldmode, rtx x, int unsignedp)
       && (GET_MODE_PRECISION (subreg_promoted_mode (x))
 	  >= GET_MODE_PRECISION (int_mode))
       && SUBREG_CHECK_PROMOTED_SIGN (x, unsignedp))
-    x = gen_lowpart (int_mode, SUBREG_REG (x));
+    {
+      scalar_int_mode int_orig_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))
+	{
+	  SUBREG_PROMOTED_VAR_P (x) = 1;
+	  SUBREG_PROMOTED_SET (x, unsignedp);
+	}
+    }
 
   if (GET_MODE (x) != VOIDmode)
     oldmode = GET_MODE (x);
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index c81e27e..a75f6b2 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -1511,12 +1511,28 @@  simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
 	 target mode is the same as the variable's promotion.  */
       if (GET_CODE (op) == SUBREG
 	  && SUBREG_PROMOTED_VAR_P (op)
-	  && SUBREG_PROMOTED_SIGNED_P (op)
-	  && !paradoxical_subreg_p (mode, GET_MODE (SUBREG_REG (op))))
+	  && SUBREG_PROMOTED_SIGNED_P (op))
 	{
-	  temp = rtl_hooks.gen_lowpart_no_emit (mode, SUBREG_REG (op));
-	  if (temp)
-	    return temp;
+	  rtx subreg = SUBREG_REG (op);
+	  machine_mode subreg_mode = GET_MODE (subreg);
+	  if (!paradoxical_subreg_p (mode, subreg_mode))
+	    {
+	      temp = rtl_hooks.gen_lowpart_no_emit (mode, subreg);
+	      if (temp)
+		{
+		  /* Preserve SUBREG_PROMOTED_VAR_P.  */
+		  if (partial_subreg_p (temp))
+		    {
+		      SUBREG_PROMOTED_VAR_P (temp) = 1;
+		      SUBREG_PROMOTED_SET (temp, 1);
+		    }
+		  return temp;
+		}
+	    }
+	  else
+	    /* Sign-extending a sign-extended subreg.  */
+	    return simplify_gen_unary (SIGN_EXTEND, mode,
+				       subreg, subreg_mode);
 	}
 
       /* (sign_extend:M (sign_extend:N <X>)) is (sign_extend:M <X>).
@@ -1630,12 +1646,28 @@  simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
 	 target mode is the same as the variable's promotion.  */
       if (GET_CODE (op) == SUBREG
 	  && SUBREG_PROMOTED_VAR_P (op)
-	  && SUBREG_PROMOTED_UNSIGNED_P (op)
-	  && !paradoxical_subreg_p (mode, GET_MODE (SUBREG_REG (op))))
+	  && SUBREG_PROMOTED_UNSIGNED_P (op))
 	{
-	  temp = rtl_hooks.gen_lowpart_no_emit (mode, SUBREG_REG (op));
-	  if (temp)
-	    return temp;
+	  rtx subreg = SUBREG_REG (op);
+	  machine_mode subreg_mode = GET_MODE (subreg);
+	  if (!paradoxical_subreg_p (mode, subreg_mode))
+	    {
+	      temp = rtl_hooks.gen_lowpart_no_emit (mode, subreg);
+	      if (temp)
+		{
+		  /* Preserve SUBREG_PROMOTED_VAR_P.  */
+		  if (partial_subreg_p (temp))
+		    {
+		      SUBREG_PROMOTED_VAR_P (temp) = 1;
+		      SUBREG_PROMOTED_SET (temp, 0);
+		    }
+		  return temp;
+		}
+	    }
+	  else
+	    /* Zero-extending a zero-extended subreg.  */
+	    return simplify_gen_unary (ZERO_EXTEND, mode,
+				       subreg, subreg_mode);
 	}
 
       /* Extending a widening multiplication should be canonicalized to