* [PATCH] stor-layout: Create DECL_BIT_FIELD_REPRESENTATIVE even for bitfields in unions [PR101062]
@ 2021-06-16 7:45 Jakub Jelinek
2021-06-16 9:54 ` Richard Biener
2021-06-18 8:30 ` [PATCH] stor-layout: Don't create DECL_BIT_FIELD_REPRESENTATIVE for QUAL_UNION_TYPE [PR101062] Jakub Jelinek
0 siblings, 2 replies; 4+ messages in thread
From: Jakub Jelinek @ 2021-06-16 7:45 UTC (permalink / raw)
To: Richard Biener; +Cc: gcc-patches
Hi!
The following testcase is miscompiled on x86_64-linux, the bitfield store
is implemented as a RMW 64-bit operation at d+24 when the d variable has
size of only 28 bytes and scheduling moves in between the R and W part
a store to a different variable that happens to be right after the d
variable.
The reason for this is that we weren't creating
DECL_BIT_FIELD_REPRESENTATIVEs for bitfields in unions.
The following patch does create them, but treats all such bitfields as if
they were in a structure where the particular bitfield is the only field.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2021-06-16 Jakub Jelinek <jakub@redhat.com>
PR middle-end/101062
* stor-layout.c (finish_bitfield_representative): For fields in unions
assume nextf is always NULL.
(finish_bitfield_layout): Compute bit field representatives also in
unions, but handle it as if each bitfield was the only field in the
aggregate.
* gcc.dg/pr101062.c: New test.
--- gcc/stor-layout.c.jj 2021-03-30 18:11:52.537092233 +0200
+++ gcc/stor-layout.c 2021-06-15 10:58:59.244353965 +0200
@@ -2072,9 +2072,14 @@ finish_bitfield_representative (tree rep
bitsize = (bitsize + BITS_PER_UNIT - 1) & ~(BITS_PER_UNIT - 1);
/* Now nothing tells us how to pad out bitsize ... */
- nextf = DECL_CHAIN (field);
- while (nextf && TREE_CODE (nextf) != FIELD_DECL)
- nextf = DECL_CHAIN (nextf);
+ if (TREE_CODE (DECL_CONTEXT (field)) == RECORD_TYPE)
+ {
+ nextf = DECL_CHAIN (field);
+ while (nextf && TREE_CODE (nextf) != FIELD_DECL)
+ nextf = DECL_CHAIN (nextf);
+ }
+ else
+ nextf = NULL_TREE;
if (nextf)
{
tree maxsize;
@@ -2167,13 +2172,6 @@ finish_bitfield_layout (tree t)
tree field, prev;
tree repr = NULL_TREE;
- /* Unions would be special, for the ease of type-punning optimizations
- we could use the underlying type as hint for the representative
- if the bitfield would fit and the representative would not exceed
- the union in size. */
- if (TREE_CODE (t) != RECORD_TYPE)
- return;
-
for (prev = NULL_TREE, field = TYPE_FIELDS (t);
field; field = DECL_CHAIN (field))
{
@@ -2233,7 +2231,13 @@ finish_bitfield_layout (tree t)
if (repr)
DECL_BIT_FIELD_REPRESENTATIVE (field) = repr;
- prev = field;
+ if (TREE_CODE (t) == RECORD_TYPE)
+ prev = field;
+ else if (repr)
+ {
+ finish_bitfield_representative (repr, field);
+ repr = NULL_TREE;
+ }
}
if (repr)
--- gcc/testsuite/gcc.dg/pr101062.c.jj 2021-06-15 10:42:58.642919880 +0200
+++ gcc/testsuite/gcc.dg/pr101062.c 2021-06-15 10:42:40.897171191 +0200
@@ -0,0 +1,29 @@
+/* PR middle-end/101062 */
+/* { dg-do run } */
+/* { dg-options "-O2 -fno-toplevel-reorder -frename-registers" } */
+
+union U { signed b : 5; };
+int c;
+volatile union U d[7] = { { 8 } };
+short e = 1;
+
+__attribute__((noipa)) void
+foo ()
+{
+ d[6].b = 0;
+ d[6].b = 0;
+ d[6].b = 0;
+ d[6].b = 0;
+ d[6].b = 0;
+ e = 0;
+ c = 0;
+}
+
+int
+main ()
+{
+ foo ();
+ if (e != 0)
+ __builtin_abort ();
+ return 0;
+}
Jakub
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] stor-layout: Create DECL_BIT_FIELD_REPRESENTATIVE even for bitfields in unions [PR101062]
2021-06-16 7:45 [PATCH] stor-layout: Create DECL_BIT_FIELD_REPRESENTATIVE even for bitfields in unions [PR101062] Jakub Jelinek
@ 2021-06-16 9:54 ` Richard Biener
2021-06-18 8:30 ` [PATCH] stor-layout: Don't create DECL_BIT_FIELD_REPRESENTATIVE for QUAL_UNION_TYPE [PR101062] Jakub Jelinek
1 sibling, 0 replies; 4+ messages in thread
From: Richard Biener @ 2021-06-16 9:54 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: gcc-patches
On Wed, 16 Jun 2021, Jakub Jelinek wrote:
> Hi!
>
> The following testcase is miscompiled on x86_64-linux, the bitfield store
> is implemented as a RMW 64-bit operation at d+24 when the d variable has
> size of only 28 bytes and scheduling moves in between the R and W part
> a store to a different variable that happens to be right after the d
> variable.
>
> The reason for this is that we weren't creating
> DECL_BIT_FIELD_REPRESENTATIVEs for bitfields in unions.
>
> The following patch does create them, but treats all such bitfields as if
> they were in a structure where the particular bitfield is the only field.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Thanks,
Richard.
> 2021-06-16 Jakub Jelinek <jakub@redhat.com>
>
> PR middle-end/101062
> * stor-layout.c (finish_bitfield_representative): For fields in unions
> assume nextf is always NULL.
> (finish_bitfield_layout): Compute bit field representatives also in
> unions, but handle it as if each bitfield was the only field in the
> aggregate.
>
> * gcc.dg/pr101062.c: New test.
>
> --- gcc/stor-layout.c.jj 2021-03-30 18:11:52.537092233 +0200
> +++ gcc/stor-layout.c 2021-06-15 10:58:59.244353965 +0200
> @@ -2072,9 +2072,14 @@ finish_bitfield_representative (tree rep
> bitsize = (bitsize + BITS_PER_UNIT - 1) & ~(BITS_PER_UNIT - 1);
>
> /* Now nothing tells us how to pad out bitsize ... */
> - nextf = DECL_CHAIN (field);
> - while (nextf && TREE_CODE (nextf) != FIELD_DECL)
> - nextf = DECL_CHAIN (nextf);
> + if (TREE_CODE (DECL_CONTEXT (field)) == RECORD_TYPE)
> + {
> + nextf = DECL_CHAIN (field);
> + while (nextf && TREE_CODE (nextf) != FIELD_DECL)
> + nextf = DECL_CHAIN (nextf);
> + }
> + else
> + nextf = NULL_TREE;
> if (nextf)
> {
> tree maxsize;
> @@ -2167,13 +2172,6 @@ finish_bitfield_layout (tree t)
> tree field, prev;
> tree repr = NULL_TREE;
>
> - /* Unions would be special, for the ease of type-punning optimizations
> - we could use the underlying type as hint for the representative
> - if the bitfield would fit and the representative would not exceed
> - the union in size. */
> - if (TREE_CODE (t) != RECORD_TYPE)
> - return;
> -
> for (prev = NULL_TREE, field = TYPE_FIELDS (t);
> field; field = DECL_CHAIN (field))
> {
> @@ -2233,7 +2231,13 @@ finish_bitfield_layout (tree t)
> if (repr)
> DECL_BIT_FIELD_REPRESENTATIVE (field) = repr;
>
> - prev = field;
> + if (TREE_CODE (t) == RECORD_TYPE)
> + prev = field;
> + else if (repr)
> + {
> + finish_bitfield_representative (repr, field);
> + repr = NULL_TREE;
> + }
> }
>
> if (repr)
> --- gcc/testsuite/gcc.dg/pr101062.c.jj 2021-06-15 10:42:58.642919880 +0200
> +++ gcc/testsuite/gcc.dg/pr101062.c 2021-06-15 10:42:40.897171191 +0200
> @@ -0,0 +1,29 @@
> +/* PR middle-end/101062 */
> +/* { dg-do run } */
> +/* { dg-options "-O2 -fno-toplevel-reorder -frename-registers" } */
> +
> +union U { signed b : 5; };
> +int c;
> +volatile union U d[7] = { { 8 } };
> +short e = 1;
> +
> +__attribute__((noipa)) void
> +foo ()
> +{
> + d[6].b = 0;
> + d[6].b = 0;
> + d[6].b = 0;
> + d[6].b = 0;
> + d[6].b = 0;
> + e = 0;
> + c = 0;
> +}
> +
> +int
> +main ()
> +{
> + foo ();
> + if (e != 0)
> + __builtin_abort ();
> + return 0;
> +}
>
> Jakub
>
>
--
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH] stor-layout: Don't create DECL_BIT_FIELD_REPRESENTATIVE for QUAL_UNION_TYPE [PR101062]
2021-06-16 7:45 [PATCH] stor-layout: Create DECL_BIT_FIELD_REPRESENTATIVE even for bitfields in unions [PR101062] Jakub Jelinek
2021-06-16 9:54 ` Richard Biener
@ 2021-06-18 8:30 ` Jakub Jelinek
2021-06-18 9:17 ` Richard Biener
1 sibling, 1 reply; 4+ messages in thread
From: Jakub Jelinek @ 2021-06-18 8:30 UTC (permalink / raw)
To: Richard Biener, Eric Botcazou; +Cc: gcc-patches
On Wed, Jun 16, 2021 at 09:45:17AM +0200, Jakub Jelinek via Gcc-patches wrote:
> The following patch does create them, but treats all such bitfields as if
> they were in a structure where the particular bitfield is the only field.
While the patch passed bootstrap/regtest on the trunk, when trying to
backport it to 11 branch the bootstrap failed with
atree.ads:3844:34: size for "Node_Record" too small
errors. Turns out the error is not about size being too small, but actually
about size being non-constant, and comes from:
/* In a FIELD_DECL of a RECORD_TYPE, this is a pointer to the storage
representative FIELD_DECL. */
#define DECL_BIT_FIELD_REPRESENTATIVE(NODE) \
(FIELD_DECL_CHECK (NODE)->field_decl.qualifier)
/* For a FIELD_DECL in a QUAL_UNION_TYPE, records the expression, which
if nonzero, indicates that the field occupies the type. */
#define DECL_QUALIFIER(NODE) (FIELD_DECL_CHECK (NODE)->field_decl.qualifier)
so by setting up DECL_BIT_FIELD_REPRESENTATIVE in QUAL_UNION_TYPE we
actually set or modify DECL_QUALIFIER and then construct size as COND_EXPRs
with those bit field representatives (e.g. with array type) as conditions
which doesn't fold into constant.
The following patch fixes it by not creating DECL_BIT_FIELD_REPRESENTATIVEs
for QUAL_UNION_TYPE as there is nowhere to store them,
Bootstrapped/regtested on x86_64-linux and i686-linux (both trunk and
11 branch - there on top of the earlier patch backport). Ok for trunk and
the backport?
Shall we change tree.h to document that DECL_BIT_FIELD_REPRESENTATIVE
is valid also on UNION_TYPE?
I see:
tree-ssa-alias.c- if (TREE_CODE (type1) == RECORD_TYPE
tree-ssa-alias.c: && DECL_BIT_FIELD_REPRESENTATIVE (field1))
tree-ssa-alias.c: field1 = DECL_BIT_FIELD_REPRESENTATIVE (field1);
tree-ssa-alias.c- if (TREE_CODE (type2) == RECORD_TYPE
tree-ssa-alias.c: && DECL_BIT_FIELD_REPRESENTATIVE (field2))
tree-ssa-alias.c: field2 = DECL_BIT_FIELD_REPRESENTATIVE (field2);
Shall we change that to || == UNION_TYPE or do we assume all fields
are overlapping in a UNION_TYPE already?
At other spots (asan, ubsan, expr.c) it is unclear what will happen
if they see a QUAL_UNION_TYPE with a DECL_QUALIFIER (or does the Ada FE
lower that somehow)?
2021-06-18 Jakub Jelinek <jakub@redhat.com>
PR middle-end/101062
* stor-layout.c (finish_bitfield_layout): Don't add bitfield
representatives in QUAL_UNION_TYPE.
--- gcc/stor-layout.c.jj 2021-06-16 12:17:49.254221954 +0200
+++ gcc/stor-layout.c 2021-06-17 11:36:13.011822974 +0200
@@ -2172,6 +2172,9 @@ finish_bitfield_layout (tree t)
tree field, prev;
tree repr = NULL_TREE;
+ if (TREE_CODE (t) == QUAL_UNION_TYPE)
+ return;
+
for (prev = NULL_TREE, field = TYPE_FIELDS (t);
field; field = DECL_CHAIN (field))
{
Jakub
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] stor-layout: Don't create DECL_BIT_FIELD_REPRESENTATIVE for QUAL_UNION_TYPE [PR101062]
2021-06-18 8:30 ` [PATCH] stor-layout: Don't create DECL_BIT_FIELD_REPRESENTATIVE for QUAL_UNION_TYPE [PR101062] Jakub Jelinek
@ 2021-06-18 9:17 ` Richard Biener
0 siblings, 0 replies; 4+ messages in thread
From: Richard Biener @ 2021-06-18 9:17 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: Eric Botcazou, gcc-patches
On Fri, 18 Jun 2021, Jakub Jelinek wrote:
> On Wed, Jun 16, 2021 at 09:45:17AM +0200, Jakub Jelinek via Gcc-patches wrote:
> > The following patch does create them, but treats all such bitfields as if
> > they were in a structure where the particular bitfield is the only field.
>
> While the patch passed bootstrap/regtest on the trunk, when trying to
> backport it to 11 branch the bootstrap failed with
> atree.ads:3844:34: size for "Node_Record" too small
> errors. Turns out the error is not about size being too small, but actually
> about size being non-constant, and comes from:
> /* In a FIELD_DECL of a RECORD_TYPE, this is a pointer to the storage
> representative FIELD_DECL. */
> #define DECL_BIT_FIELD_REPRESENTATIVE(NODE) \
> (FIELD_DECL_CHECK (NODE)->field_decl.qualifier)
>
> /* For a FIELD_DECL in a QUAL_UNION_TYPE, records the expression, which
> if nonzero, indicates that the field occupies the type. */
> #define DECL_QUALIFIER(NODE) (FIELD_DECL_CHECK (NODE)->field_decl.qualifier)
> so by setting up DECL_BIT_FIELD_REPRESENTATIVE in QUAL_UNION_TYPE we
> actually set or modify DECL_QUALIFIER and then construct size as COND_EXPRs
> with those bit field representatives (e.g. with array type) as conditions
> which doesn't fold into constant.
>
> The following patch fixes it by not creating DECL_BIT_FIELD_REPRESENTATIVEs
> for QUAL_UNION_TYPE as there is nowhere to store them,
>
> Bootstrapped/regtested on x86_64-linux and i686-linux (both trunk and
> 11 branch - there on top of the earlier patch backport). Ok for trunk and
> the backport?
>
> Shall we change tree.h to document that DECL_BIT_FIELD_REPRESENTATIVE
> is valid also on UNION_TYPE?
I think so.
> I see:
> tree-ssa-alias.c- if (TREE_CODE (type1) == RECORD_TYPE
> tree-ssa-alias.c: && DECL_BIT_FIELD_REPRESENTATIVE (field1))
> tree-ssa-alias.c: field1 = DECL_BIT_FIELD_REPRESENTATIVE (field1);
> tree-ssa-alias.c- if (TREE_CODE (type2) == RECORD_TYPE
> tree-ssa-alias.c: && DECL_BIT_FIELD_REPRESENTATIVE (field2))
> tree-ssa-alias.c: field2 = DECL_BIT_FIELD_REPRESENTATIVE (field2);
> Shall we change that to || == UNION_TYPE or do we assume all fields
> are overlapping in a UNION_TYPE already?
We don't assume that - for example the Fortran FE uses union types
to lay out equivalences which have multiple members at non-zero offsets,
eventually partly overlapping. IIRC at least.
But Fortran doesn't have bitfields (does it?). Still I guess updating
the checks would be prefered.
> At other spots (asan, ubsan, expr.c) it is unclear what will happen
> if they see a QUAL_UNION_TYPE with a DECL_QUALIFIER (or does the Ada FE
> lower that somehow)?
I don't think we see implicit uses of DECL_QUALIFIER, instead I think
that's reflected into DECL_FIELD_OFFSET.
OK.
Richard.
> 2021-06-18 Jakub Jelinek <jakub@redhat.com>
>
> PR middle-end/101062
> * stor-layout.c (finish_bitfield_layout): Don't add bitfield
> representatives in QUAL_UNION_TYPE.
>
> --- gcc/stor-layout.c.jj 2021-06-16 12:17:49.254221954 +0200
> +++ gcc/stor-layout.c 2021-06-17 11:36:13.011822974 +0200
> @@ -2172,6 +2172,9 @@ finish_bitfield_layout (tree t)
> tree field, prev;
> tree repr = NULL_TREE;
>
> + if (TREE_CODE (t) == QUAL_UNION_TYPE)
> + return;
> +
> for (prev = NULL_TREE, field = TYPE_FIELDS (t);
> field; field = DECL_CHAIN (field))
> {
>
>
> Jakub
>
>
--
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-06-16 7:45 [PATCH] stor-layout: Create DECL_BIT_FIELD_REPRESENTATIVE even for bitfields in unions [PR101062] Jakub Jelinek
2021-06-16 9:54 ` Richard Biener
2021-06-18 8:30 ` [PATCH] stor-layout: Don't create DECL_BIT_FIELD_REPRESENTATIVE for QUAL_UNION_TYPE [PR101062] Jakub Jelinek
2021-06-18 9:17 ` Richard Biener
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