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* [Bug middle-end/113395] New: RTL expansion drops MEM_EXPR
@ 2024-01-15 10:49 rguenth at gcc dot gnu.org
2024-01-15 11:54 ` [Bug middle-end/113395] " rguenth at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-01-15 10:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113395
Bug ID: 113395
Summary: RTL expansion drops MEM_EXPR
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
struct S {
signed m : 7;
signed e : 2;
} g;
void
k()
{
g.e ^= 1;
}
expands as
(insn 8 7 0 (parallel [
(set (mem/j/c:HI (reg/f:DI 100) [0 +0 S2 A32])
(xor:HI (mem/j/c:HI (reg/f:DI 100) [0 +0 S2 A32])
(reg:HI 101)))
(clobber (reg:CC 17 flags))
]) "t.c":9:7 -1
(nil))
similar g.e = 1;
(insn 9 8 10 (set (reg:HI 102)
(mem/j/c:HI (reg/f:DI 101) [0 +0 S2 A32])) "t.c":9:7 -1
(nil))
...
(insn 12 11 0 (set (mem/j/c:HI (reg/f:DI 101) [0 +0 S2 A32])
(reg:HI 104)) "t.c":9:7 -1
(nil))
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/113395] RTL expansion drops MEM_EXPR
2024-01-15 10:49 [Bug middle-end/113395] New: RTL expansion drops MEM_EXPR rguenth at gcc dot gnu.org
@ 2024-01-15 11:54 ` rguenth at gcc dot gnu.org
2024-01-15 11:57 ` [Bug middle-end/113395] RTL expansion of bitfield accesses " rguenth at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-01-15 11:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113395
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Because of
#0 adjust_address_1 (memref=0x7ffff71e8db0, mode=E_HImode, offset=...,
validate=1, adjust_address=1, adjust_object=1, size=...)
at /space/rguenther/src/gcc/gcc/emit-rtl.cc:2409
#1 0x00000000011459af in narrow_bit_field_mem (mem=0x7ffff71e8db0,
mode=HImode, bitsize=2, bitnum=7, new_bitnum=0x7fffffffc8c0)
at /space/rguenther/src/gcc/gcc/expmed.cc:453
#2 0x0000000001145d1c in adjust_bit_field_mem_for_reg (pattern=EP_insv,
op0=0x7ffff71e8db0, bitsize=2, bitnum=7, bitregion_start=...,
bitregion_end=..., fieldmode=E_VOIDmode, new_bitnum=0x7fffffffc8c0)
at /space/rguenther/src/gcc/gcc/expmed.cc:511
#3 0x00000000011483bb in store_integral_bit_field (op0=0x7ffff71e8db0,
op0_mode=SImode, bitsize=2, bitnum=7, bitregion_start=...,
bitregion_end=..., fieldmode=E_VOIDmode, value=0x7ffff70124a0,
reverse=false, fallback_p=true)
at /space/rguenther/src/gcc/gcc/expmed.cc:1086
#4 0x00000000011476a0 in store_bit_field_1 (str_rtx=0x7ffff71e8db0,
bitsize=..., bitnum=..., bitregion_start=..., bitregion_end=...,
fieldmode=E_VOIDmode, value=0x7ffff70124a0, reverse=false,
fallback_p=true, undefined_p=false)
at /space/rguenther/src/gcc/gcc/expmed.cc:887
#5 0x0000000001148c31 in store_bit_field (str_rtx=0x7ffff71e8db0,
bitsize=..., bitnum=..., bitregion_start=..., bitregion_end=...,
fieldmode=E_VOIDmode, value=0x7ffff70124a0, reverse=false,
--Type <RET> for more, q to quit, c to continue without paging--
) at /space/rguenther/src/gcc/gcc/expmed.cc:1194
#6 0x000000000117dde0 in store_field (target=0x7ffff71e8db0, bitsize=...,
bitpos=..., bitregion_start=..., bitregion_end=..., mode=E_VOIDmode,
exp=<integer_cst 0x7ffff71c4ca8>, alias_set=1, nontemporal=false,
reverse=false) at /space/rguenther/src/gcc/gcc/expr.cc:8245
#7 0x0000000001174b21 in expand_assignment (
to=<component_ref 0x7ffff71e07b0>, from=<integer_cst 0x7ffff71c4ca8>,
nontemporal=false) at /space/rguenther/src/gcc/gcc/expr.cc:6303
and we run into
if (maybe_ne (size, 0))
{
/* Drop the object if the new right end is not within its bounds. */
if (adjust_object && maybe_gt (offset + size, attrs.size))
{
attrs.expr = NULL_TREE;
attrs.alias = 0;
}
as attrs.size is originally 1 and we are creating a two byte HImode access.
IMHO it's the fault of how we set up the initial memory attributes which
come via expand_assignment doing
tem = get_inner_reference (to, &bitsize, &bitpos, &offset, &mode1,
&unsignedp, &reversep, &volatilep);
..
if (TREE_CODE (to) == COMPONENT_REF
&& DECL_BIT_FIELD_TYPE (TREE_OPERAND (to, 1)))
get_bit_range (&bitregion_start, &bitregion_end, to, &bitpos, &offset);
..
to_rtx = expand_expr (tem, NULL_RTX, VOIDmode, EXPAND_WRITE);
..
if (MEM_P (to_rtx))
{
/* If the field is at offset zero, we could have been given the
DECL_RTX of the parent struct. Don't munge it. */
to_rtx = shallow_copy_rtx (to_rtx);
set_mem_attributes_minus_bitpos (to_rtx, to, 0, bitpos);
if (volatilep)
MEM_VOLATILE_P (to_rtx) = 1;
that's an unfortunate setup to eventually widen the setup.
RTL alias analysis then has to rely on find_base_term to perform it's
bogus optimistic points-to analysis.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/113395] RTL expansion of bitfield accesses drops MEM_EXPR
2024-01-15 10:49 [Bug middle-end/113395] New: RTL expansion drops MEM_EXPR rguenth at gcc dot gnu.org
2024-01-15 11:54 ` [Bug middle-end/113395] " rguenth at gcc dot gnu.org
@ 2024-01-15 11:57 ` rguenth at gcc dot gnu.org
2024-01-15 22:55 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-01-15 11:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113395
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|RTL expansion drops |RTL expansion of bitfield
|MEM_EXPR |accesses drops MEM_EXPR
Blocks| |113255
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
gcc.dg/tree-ssa/pr94969.c for example misses RTL PRE when we dumb down
find_base_term to be conservatively correct. GIMPLE invariant motion
doesn't handle the involved aggregate copy which on RTL maps to SImode.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113255
[Bug 113255] [11/12/13/14 Regression] wrong code with -O2 -mtune=k8
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/113395] RTL expansion of bitfield accesses drops MEM_EXPR
2024-01-15 10:49 [Bug middle-end/113395] New: RTL expansion drops MEM_EXPR rguenth at gcc dot gnu.org
2024-01-15 11:54 ` [Bug middle-end/113395] " rguenth at gcc dot gnu.org
2024-01-15 11:57 ` [Bug middle-end/113395] RTL expansion of bitfield accesses " rguenth at gcc dot gnu.org
@ 2024-01-15 22:55 ` pinskia at gcc dot gnu.org
2024-01-15 22:58 ` pinskia at gcc dot gnu.org
2024-01-16 9:27 ` rguenth at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-01-15 22:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113395
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Last reconfirmed| |2024-01-15
Status|UNCONFIRMED |NEW
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I am almost positive there is a dup of this bug somewhere ...
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/113395] RTL expansion of bitfield accesses drops MEM_EXPR
2024-01-15 10:49 [Bug middle-end/113395] New: RTL expansion drops MEM_EXPR rguenth at gcc dot gnu.org
` (2 preceding siblings ...)
2024-01-15 22:55 ` pinskia at gcc dot gnu.org
@ 2024-01-15 22:58 ` pinskia at gcc dot gnu.org
2024-01-16 9:27 ` rguenth at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-01-15 22:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113395
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Depends on| |45274
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #3)
> I am almost positive there is a dup of this bug somewhere ...
Yes PR 45274 where the aliasing set is 0 ...
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45274
[Bug 45274] __restrict__ type qualifier does not work on pointers to bitfields
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/113395] RTL expansion of bitfield accesses drops MEM_EXPR
2024-01-15 10:49 [Bug middle-end/113395] New: RTL expansion drops MEM_EXPR rguenth at gcc dot gnu.org
` (3 preceding siblings ...)
2024-01-15 22:58 ` pinskia at gcc dot gnu.org
@ 2024-01-16 9:27 ` rguenth at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-01-16 9:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113395
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Without fully lowering this on GIMPLE we could substitute the representative
for the bitfield member in the MEM_EXPR and adjust adjust_address_1 to
instead of using attrs.size to constrain the extent of the object designated
by MEM_EXPR re-discover it. (I wonder if MEM_SIZE needs to be exact
in a must-def way - ao_ref_from_mem certainly treats it that way instead
of getting the size from the mode for non-BLKmode accesses)
That said, lowering on GIMPLE is the way to go. Even iff only right before
RTL expansion ...
^ permalink raw reply [flat|nested] 6+ messages in thread
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2024-01-15 10:49 [Bug middle-end/113395] New: RTL expansion drops MEM_EXPR rguenth at gcc dot gnu.org
2024-01-15 11:54 ` [Bug middle-end/113395] " rguenth at gcc dot gnu.org
2024-01-15 11:57 ` [Bug middle-end/113395] RTL expansion of bitfield accesses " rguenth at gcc dot gnu.org
2024-01-15 22:55 ` pinskia at gcc dot gnu.org
2024-01-15 22:58 ` pinskia at gcc dot gnu.org
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