* [PATCH] Fix PR55876 - Make generation of paradoxical subreg in widen_operand more robust
[not found] <50EA9FDD.6000803@mentor.com>
@ 2013-01-07 10:16 ` Tom de Vries
2013-01-07 17:48 ` Richard Henderson
0 siblings, 1 reply; 4+ messages in thread
From: Tom de Vries @ 2013-01-07 10:16 UTC (permalink / raw)
To: Richard Henderson; +Cc: Steve Ellcey, Andrew Pinski, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 6211 bytes --]
[with CC to gcc-patches]
-------- Original Message --------
Subject: [PATCH] Fix PR55876 - Make generation of paradoxical subreg in
widen_operand more robust
Date: Mon, 07 Jan 2013 11:13:49 +0100
From: Tom de Vries <Tom_deVries@mentor.com>
To: Richard Henderson <rth@redhat.com>
CC: Steve Ellcey <sellcey@mips.com>, Andrew Pinski <pinskia@gmail.com>
Richard,
Consider test-case test.c:
...
static inline unsigned char
bar (const char *b)
{
unsigned char used = 0;
int i;
for (i = 0; i < 4; ++i)
if (b[i] != 'F')
used = 1;
return used;
}
static char buffer[8];
unsigned char
foo (void)
{
return bar (buffer) ? 0 : 1;
}
...
When compiling test.c with a mips compiler, this ICE triggers:
...
$ ./install/bin/mips-linux-gnu-gcc -O3 test.c -S -mabi=64 -march=mips64
test.c: In function 'foo':
test.c:19:3: internal compiler error: in gen_rtx_SUBREG, at emit-rtl.c:776
return bar (buffer) ? 0 : 1;
...
The ICE is introduced by revision r193539 discussed at
http://gcc.gnu.org/ml/gcc-patches/2012-11/msg01148.html .
The representation of foo just before expand is this:
...
foo ()
{
unsigned charD.13 usedD.1407;
charD.2 _7;
unsigned charD.13 _13;
charD.2 _19;
charD.2 _28;
charD.2 _37;
;; basic block 2, loop depth 0
;; pred: ENTRY
# VUSE <.MEM_1(D)>
_19 = MEM[(const charD.2 *)&bufferD.1387];
used_20 = _19 != 70 ? 1 : 0;
# VUSE <.MEM_1(D)>
_28 = MEM[(const charD.2 *)&bufferD.1387 + 1B];
used_29 = _28 == 70 ? used_20 : 1;
# VUSE <.MEM_1(D)>
_37 = MEM[(const charD.2 *)&bufferD.1387 + 2B];
used_38 = _37 == 70 ? used_29 : 1;
# VUSE <.MEM_1(D)>
_7 = MEM[(const charD.2 *)&bufferD.1387 + 3B];
used_10 = _7 == 70 ? used_38 : 1;
_13 = used_10 ^ 1;
# VUSE <.MEM_1(D)>
return _13;
;; succ: EXIT
}
...
The used_10 operand is in a DImode reg because r193539 allows it to be promoted
while expanding
used_10 = _7 == 70 ? used_38 : 1
in expand_cond_expr_using_cmove.
The ICE happens during expansion of
_13 = used_10 ^ 1
when trying to widen the DIMode reg for use_10 from QImode to SImode:
...
#6 0x085d7da5 in widen_operand (op=0xf7cd2ec0, mode=SImode, oldmode=QImode,
unsignedp=1, no_extend=1) at
/home/vries/local/mips/upstream/src/gcc-mainline/gcc/optabs.c:333
333 return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
(gdb) call debug_rtx (op)
(reg:DI 222 [ used+-7 ])
...
And although the comment in widen_operand states that we're generating a
paradoxical subreg:
...
/* If MODE is no wider than a single word, we return a paradoxical
SUBREG. */
if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD)
return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
...
it's not because mode == SImode and GET_MODE (op) == DImode.
Then validate_subreg triggers the ICE in gen_rtx_SUBREG by returning false here:
...
/* For pseudo registers, we want most of the same checks. Namely:
If the register no larger than a word, the subreg must be lowpart.
If the register is larger than a word, the subreg must be the lowpart
of a subword. A subreg does *not* perform arbitrary bit extraction.
Given that we've already checked mode/offset alignment, we only have
to check subword subregs here. */
if (osize < UNITS_PER_WORD
&& ! (lra_in_progress && (FLOAT_MODE_P (imode) || FLOAT_MODE_P (omode))))
{
enum machine_mode wmode = isize > UNITS_PER_WORD ? word_mode : imode;
unsigned int low_off = subreg_lowpart_offset (omode, wmode);
if (offset % UNITS_PER_WORD != low_off)
return false;
}
...
For a valid pseudo subreg with outer mode SImode and inner mode DImode we need
the offset corresponding to the lowpart, which is 4 for -EB. But since we were
trying to generate a paradoxical subreg, the offset is 0. This explains why the
assert doesn't trigger with -EL.
Attached patch (build and tested for target mips-linux-gnu) prevents the ICE by
checking in widen_operand whether the result of the gen_rtx_SUBREG call would
indeed be a paradoxical subreg. As a consequence, it handles this case now here:
...
/* Otherwise, get an object of MODE, clobber it, and set the low-order
part to OP. */
result = gen_reg_rtx (mode);
emit_clobber (result);
emit_move_insn (gen_lowpart (GET_MODE (op), result), op);
return result;
...
So the generated code is this:
...
(insn 34 33 35 2 (clobber (reg:SI 228)) -1
(nil))
(insn 35 34 36 2 (set (subreg:DI (reg:SI 228) 0)
(reg:DI 222 [ usedD.1407+-7 ])) -1
(nil))
(insn 36 35 37 2 (set (reg:SI 229)
(xor:SI (reg:SI 228)
(const_int 1 [0x1]))) -1
...
which is correct.
I've just realized that this is probably a too conservative fix. Using this patch:
...
Index: gcc/optabs.c
===================================================================
--- gcc/optabs.c (revision 194898)
+++ gcc/optabs.c (working copy)
@@ -327,10 +327,15 @@ widen_operand (rtx op, enum machine_mode
&& SUBREG_PROMOTED_UNSIGNED_P (op) == unsignedp))
return convert_modes (mode, oldmode, op, unsignedp);
- /* If MODE is no wider than a single word, we return a paradoxical
- SUBREG. */
+ /* If MODE is no wider than a single word, we return a
+ lowpart or paradoxical SUBREG. */
if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD)
- return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
+ {
+ if (GET_MODE_SIZE (mode) < GET_MODE_SIZE (GET_MODE (op)))
+ return gen_lowpart_SUBREG (mode, op);
+ else
+ return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
+ }
/* Otherwise, get an object of MODE, clobber it, and set the low-order
part to OP. */
...
we generate this instead:
...
(insn 34 33 35 2 (set (reg:SI 228)
(xor:SI (subreg:SI (reg:DI 222 [ usedD.1407+-7 ]) 4)
(const_int 1 [0x1]))) -1
...
which is similar to what we generate with trunk for -EL.
So, is the attached patch ok for trunk?
Or should I test the more optimal patch listed above?
Or should this be fixed somewhere else?
Thanks,
- Tom
2013-01-07 Tom de Vries <tom@codesourcery.com>
PR target/55876
* optabs.c (optabs.c): Add condition to ensure that subreg will be
paradoxical.
[-- Attachment #2: widen_operand-paradoxical-subreg.patch --]
[-- Type: text/x-patch, Size: 609 bytes --]
Index: gcc/optabs.c
===================================================================
--- gcc/optabs.c (revision 194898)
+++ gcc/optabs.c (working copy)
@@ -329,7 +329,8 @@ widen_operand (rtx op, enum machine_mode
/* If MODE is no wider than a single word, we return a paradoxical
SUBREG. */
- if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD)
+ if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD
+ && GET_MODE_SIZE (mode) > GET_MODE_SIZE (GET_MODE (op)))
return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
/* Otherwise, get an object of MODE, clobber it, and set the low-order
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Fix PR55876 - Make generation of paradoxical subreg in widen_operand more robust
2013-01-07 10:16 ` [PATCH] Fix PR55876 - Make generation of paradoxical subreg in widen_operand more robust Tom de Vries
@ 2013-01-07 17:48 ` Richard Henderson
2013-01-14 14:44 ` Tom de Vries
0 siblings, 1 reply; 4+ messages in thread
From: Richard Henderson @ 2013-01-07 17:48 UTC (permalink / raw)
To: Tom de Vries; +Cc: Steve Ellcey, Andrew Pinski, gcc-patches
On 01/07/2013 02:16 AM, Tom de Vries wrote:
> - /* If MODE is no wider than a single word, we return a paradoxical
> - SUBREG. */
> + /* If MODE is no wider than a single word, we return a
> + lowpart or paradoxical SUBREG. */
> if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD)
> - return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
> + {
> + if (GET_MODE_SIZE (mode) < GET_MODE_SIZE (GET_MODE (op)))
> + return gen_lowpart_SUBREG (mode, op);
> + else
> + return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
> + }
Is there any good reason we're using gen_rtx_SUBREG directly here?
Seems like this sort of logic would be present in plain gen_lowpart,
generating the paradoxical subreg that we want.
r~
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Fix PR55876 - Make generation of paradoxical subreg in widen_operand more robust
2013-01-07 17:48 ` Richard Henderson
@ 2013-01-14 14:44 ` Tom de Vries
2013-01-15 17:12 ` Richard Henderson
0 siblings, 1 reply; 4+ messages in thread
From: Tom de Vries @ 2013-01-14 14:44 UTC (permalink / raw)
To: Richard Henderson; +Cc: Steve Ellcey, Andrew Pinski, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 1178 bytes --]
On 07/01/13 18:48, Richard Henderson wrote:
> On 01/07/2013 02:16 AM, Tom de Vries wrote:
>> - /* If MODE is no wider than a single word, we return a paradoxical
>> - SUBREG. */
>> + /* If MODE is no wider than a single word, we return a
>> + lowpart or paradoxical SUBREG. */
>> if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD)
>> - return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
>> + {
>> + if (GET_MODE_SIZE (mode) < GET_MODE_SIZE (GET_MODE (op)))
>> + return gen_lowpart_SUBREG (mode, op);
>> + else
>> + return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
>> + }
>
> Is there any good reason we're using gen_rtx_SUBREG directly here?
> Seems like this sort of logic would be present in plain gen_lowpart,
> generating the paradoxical subreg that we want.
>
Ah, didn't realize that. Attached patch uses gen_lowpart.
Bootstrapped and reg-tested on x86_64.
Build and reg-tested on mips64, -mabi=n32 and -mabi=64.
OK for trunk?
Thanks,
- Tom
2013-01-14 Tom de Vries <tom@codesourcery.com>
PR target/55876
* optabs.c (widen_operand): Use gen_lowpart instead of gen_rtx_SUBREG.
Update comment.
[-- Attachment #2: widen_operand-paradoxical-subreg.4.patch --]
[-- Type: text/x-patch, Size: 778 bytes --]
Index: gcc/optabs.c
===================================================================
--- gcc/optabs.c (revision 194898)
+++ gcc/optabs.c (working copy)
@@ -327,10 +327,10 @@ widen_operand (rtx op, enum machine_mode
&& SUBREG_PROMOTED_UNSIGNED_P (op) == unsignedp))
return convert_modes (mode, oldmode, op, unsignedp);
- /* If MODE is no wider than a single word, we return a paradoxical
+ /* If MODE is no wider than a single word, we return a lowpart or paradoxical
SUBREG. */
if (GET_MODE_SIZE (mode) <= UNITS_PER_WORD)
- return gen_rtx_SUBREG (mode, force_reg (GET_MODE (op), op), 0);
+ return gen_lowpart (mode, force_reg (GET_MODE (op), op));
/* Otherwise, get an object of MODE, clobber it, and set the low-order
part to OP. */
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Fix PR55876 - Make generation of paradoxical subreg in widen_operand more robust
2013-01-14 14:44 ` Tom de Vries
@ 2013-01-15 17:12 ` Richard Henderson
0 siblings, 0 replies; 4+ messages in thread
From: Richard Henderson @ 2013-01-15 17:12 UTC (permalink / raw)
To: Tom de Vries; +Cc: Steve Ellcey, Andrew Pinski, gcc-patches
On 01/14/2013 12:27 AM, Tom de Vries wrote:
> 2013-01-14 Tom de Vries<tom@codesourcery.com>
>
> PR target/55876
> * optabs.c (widen_operand): Use gen_lowpart instead of gen_rtx_SUBREG.
> Update comment.
Ok.
r~
^ permalink raw reply [flat|nested] 4+ messages in thread
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2013-01-07 10:16 ` [PATCH] Fix PR55876 - Make generation of paradoxical subreg in widen_operand more robust Tom de Vries
2013-01-07 17:48 ` Richard Henderson
2013-01-14 14:44 ` Tom de Vries
2013-01-15 17:12 ` Richard Henderson
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