[patch][version5]add -ftrivial-auto-var-init and variable attribute "uninitialized" to gcc
Qing Zhao
qing.zhao@oracle.com
Mon Jul 26 15:55:22 GMT 2021
Martin,
The following is the patch to fix the issues you raised in the previous email, let me know if I still miss anything:
Thanks a lot.
Qing
=====
From 14524a228b4b41b4eaaa2497455725e075126c2c Mon Sep 17 00:00:00 2001
From: Qing Zhao <qing.zhao@oracle.com>
Date: Mon, 26 Jul 2021 15:46:59 +0000
Subject: [PATCH] Fix tree-sra.c issue raised by Martin Jambor
---
gcc/testsuite/gcc.dg/auto-init-sra-1.c | 24 ++++++++++++++++++++++++
gcc/testsuite/gcc.dg/auto-init-sra-2.c | 24 ++++++++++++++++++++++++
gcc/tree-sra.c | 8 ++++++--
3 files changed, 53 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/auto-init-sra-1.c
create mode 100644 gcc/testsuite/gcc.dg/auto-init-sra-2.c
diff --git a/gcc/testsuite/gcc.dg/auto-init-sra-1.c b/gcc/testsuite/gcc.dg/auto-init-sra-1.c
new file mode 100644
index 000000000000..88fd66678f29
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/auto-init-sra-1.c
@@ -0,0 +1,24 @@
+/* Verify that SRA total scalarization will not be confused by padding
+ and also not confused by auto initialization. */
+/* { dg-do compile } */
+/* { dg-options "-O1 --param sra-max-scalarization-size-Ospeed=16 -fdump-tree-release_ssa -ftrivial-auto-var-init=zero" } */
+
+struct S
+{
+ int i;
+ unsigned short f1;
+ char f2;
+ unsigned short f3, f4;
+};
+
+
+int foo (struct S *p)
+{
+ struct S l;
+
+ l = *p;
+ l.i++;
+ *p = l;
+}
+
+/* { dg-final { scan-tree-dump-times "l;" 0 "release_ssa" } } */
diff --git a/gcc/testsuite/gcc.dg/auto-init-sra-2.c b/gcc/testsuite/gcc.dg/auto-init-sra-2.c
new file mode 100644
index 000000000000..d260f5ae934e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/auto-init-sra-2.c
@@ -0,0 +1,24 @@
+/* Verify that SRA total scalarization will not be confused by padding
+ and also not confused by auto initialization. */
+/* { dg-do compile } */
+/* { dg-options "-O1 --param sra-max-scalarization-size-Ospeed=16 -fdump-tree-release_ssa -ftrivial-auto-var-init=pattern" } */
+
+struct S
+{
+ int i;
+ unsigned short f1;
+ char f2;
+ unsigned short f3, f4;
+};
+
+
+int foo (struct S *p)
+{
+ struct S l;
+
+ l = *p;
+ l.i++;
+ *p = l;
+}
+
+/* { dg-final { scan-tree-dump-times "l;" 0 "release_ssa" } } */
diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index d1280e5f8848..bebba4deaf94 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -1195,8 +1195,10 @@ build_access_from_expr (tree expr, gimple *stmt, bool write)
{
/* This means the aggregate is accesses as a whole in a way other than an
assign statement and thus cannot be removed even if we had a scalar
- replacement for everything. */
- if (cannot_scalarize_away_bitmap)
+ replacement for everything. However, when the STMT is a call to
+ DEFERRED_INIT, we should not set this bit. */
+ if (cannot_scalarize_away_bitmap
+ && !gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
bitmap_set_bit (cannot_scalarize_away_bitmap, DECL_UID (access->base));
return true;
}
@@ -4167,6 +4169,8 @@ sra_modify_deferred_init (gimple *stmt, gimple_stmt_iterator *gsi)
tree arg0_repl = TYPE_SIZE_UNIT (TREE_TYPE (lhs_repl));
gimple_call_set_arg (stmt, 0, arg0_repl);
sra_stats.deferred_init++;
+ gcc_assert (!lhs_access->first_child);
+ return SRA_AM_MODIFIED;
}
if (lhs_access->first_child)
--
2.27.0
> On Jul 26, 2021, at 10:25 AM, Qing Zhao via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>
> HI, Martin,
>
> Thank you for the comments and suggestions on tree-sra.c changes.
>
>>> ******Compare with the 4th version, the following are the major changes:
>>>
>>> 1. delete the code for handling "grp_to_be_debug_replaced" since they are not needed per Martin Jambor's suggestion.
>>
>> sorry if I did not make myself clear in my last email, but the deferred
>> init calls should not result into setting any bits in
>> cannot_scalarize_away_bitmap in the SRA pass, otherwise you'll get
>> different optimization with and without -ftrivial-auto-var-init.
>
> It’s my bad that I missed this part of your comments…
>
>>
>> So you either need to change build_access_from_expr like I described in
>> my email
>
> Is the following the change you suggested previously:
>
> [opc@qinzhao-ol8u3-x86 gcc]$ git diff tree-sra.c
> diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
> index d1280e5f8848..c2597b705169 100644
> --- a/gcc/tree-sra.c
> +++ b/gcc/tree-sra.c
> @@ -1195,8 +1195,10 @@ build_access_from_expr (tree expr, gimple *stmt, bool write)
> {
> /* This means the aggregate is accesses as a whole in a way other than an
> assign statement and thus cannot be removed even if we had a scalar
> - replacement for everything. */
> - if (cannot_scalarize_away_bitmap)
> + replacement for everything. However, when the STMT is a call to
> + DEFERRED_INIT, we should not set this bit. */
> + if (cannot_scalarize_away_bitmap
> + && !gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
> bitmap_set_bit (cannot_scalarize_away_bitmap, DECL_UID (access->base));
> return true;
> }
>
>
>> or add the following to your patch, which is probably slightly
>> mor efficient (but it has been only very mildly tested).
>>
>>
>> diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
>> index d1280e5f884..602b0fb3a2d 100644
>> --- a/gcc/tree-sra.c
>> +++ b/gcc/tree-sra.c
>> @@ -1395,7 +1395,12 @@ scan_function (void)
>>
>> t = gimple_call_lhs (stmt);
>> if (t && !disqualify_if_bad_bb_terminating_stmt (stmt, t, NULL))
>> - ret |= build_access_from_expr (t, stmt, true);
>> + {
>> + if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
>> + ret |= !!build_access_from_expr_1 (t, stmt, true);
>> + else
>> + ret |= build_access_from_expr (t, stmt, true);
>> + }
>> break;
>
> Thanks for the patch, but I don’t quite understand the above change:
>
> When the call is IFN_DEFERRED_INIT, you used build_access_from_expr_1 instead of build_access_from_expr to avoid setting “cannot_scalarize_away_bitmap” bit.
> But why adding “!” To this call?
>
>
>>
>> case GIMPLE_ASM:
>>
>>
>>
>> And unfortunately I just spotted another potential problem in:
>>
>>> +static enum assignment_mod_result
>>> +sra_modify_deferred_init (gimple *stmt, gimple_stmt_iterator *gsi)
>>> +{
>>> + tree lhs = gimple_call_lhs (stmt);
>>> + tree init_type = gimple_call_arg (stmt, 1);
>>> + tree is_vla = gimple_call_arg (stmt, 2);
>>> +
>>> + struct access *lhs_access = get_access_for_expr (lhs);
>>> + if (!lhs_access)
>>> + return SRA_AM_NONE;
>>> +
>>> + location_t loc = gimple_location (stmt);
>>> +
>>> + if (lhs_access->grp_to_be_replaced)
>>> + {
>>> + tree lhs_repl = get_access_replacement (lhs_access);
>>> + gimple_call_set_lhs (stmt, lhs_repl);
>>> + tree arg0_repl = TYPE_SIZE_UNIT (TREE_TYPE (lhs_repl));
>>> + gimple_call_set_arg (stmt, 0, arg0_repl);
>>> + sra_stats.deferred_init++;
>>
>> I think you want to add:
>>
>> gcc_assert (!lhs_access->first_child);
>> return SRA_AM_MODIFIED;
>
> Okay.
>>
>> here, otherwise you risk that (in a case of a single-field structure)
>> the call you have just modified here...
>>
>>> + }
>>> +
>>> + if (lhs_access->first_child)
>>> + generate_subtree_deferred_init (lhs_access->first_child,
>>> + init_type, is_vla, gsi, loc);
>>> + if (lhs_access->grp_covered)
>>> + {
>>> + unlink_stmt_vdef (stmt);
>>> + gsi_remove (gsi, true);
>>
>> ...will be deleted here.
>
> I see. Thanks a lot for spotting this issue.
>>
>>> + release_defs (stmt);
>>> + return SRA_AM_REMOVED;
>>> + }
>>> +
>>> + return SRA_AM_MODIFIED;
>>> +}
>>
>> Sorry again for spotting this late and perhaps mis-communicating about
>> the cannot_scalarize_away_bitmap issue earlier. Apart from these two
>> things, I believe the tree-sra.c bits are fin.
>
> Thank you for the detailed review.
>
> Qing
>>
>> Martin
>>
>>
>>
>>
>>> 2. for Pattern init, call __builtin_clear_padding after the call to .DEFERRED_INIT to initialize the paddings to zeroes;
>>> 3. for partially or fully initialized auto variables, call __builtin_clear_padding before the real initialization to initialize
>>> the paddings to zeroes.
>>> 4. Update the documentation with padding initialization to zeroes.
>>> 5. in order to reuse __builtin_clear_padding for auto init purpose, add one more dummy argument to indiciate whether it's for auto init or not,
>>> if for auto init, do not emit error messages to avoid confusing users.
>>> 6. Add new testing cases to verify padding initializations.
>>> 7. rename some of the old testing cases to make the file name reflecting the testing purpose per Kees Cook's suggestions.
>>>
>>> ******Please see version 4 at:
>>> https://gcc.gnu.org/pipermail/gcc-patches/2021-July/574642.html
>>>
>>> ******ChangeLog is:
>>> gcc/ChangeLog:
>>>
>>> 2021-07-23 qing zhao <qing.zhao@oracle.com>
>>>
>>> * builtins.c (expand_builtin_memset): Make external visible.
>>> * builtins.h (expand_builtin_memset): Declare extern.
>>> * common.opt (ftrivial-auto-var-init=): New option.
>>> * doc/extend.texi: Document the uninitialized attribute.
>>> * doc/invoke.texi: Document -ftrivial-auto-var-init.
>>> * flag-types.h (enum auto_init_type): New enumerated type
>>> auto_init_type.
>>> * gimple-fold.c (clear_padding_type): Add one new parameter.
>>> (clear_padding_union): Likewise.
>>> (clear_padding_emit_loop): Likewise.
>>> (clear_type_padding_in_mask): Likewise.
>>> (gimple_fold_builtin_clear_padding): Handle this new parameter.
>>> * gimplify.c (gimple_add_init_for_auto_var): New function.
>>> (maybe_with_size_expr): Forword declaration.
>>> (build_deferred_init): New function.
>>> (gimple_add_padding_init_for_auto_var): New function.
>>> (gimplify_decl_expr): Add initialization to automatic variables per
>>> users' requests.
>>> (gimplify_call_expr): Add one new parameter for call to
>>> __builtin_clear_padding.
>>> (gimplify_modify_expr_rhs): Add padding initialization before
>>> gimplify_init_constructor.
>>> * internal-fn.c (INIT_PATTERN_VALUE): New macro.
>>> (expand_DEFERRED_INIT): New function.
>>> * internal-fn.def (DEFERRED_INIT): New internal function.
>>> * tree-cfg.c (verify_gimple_call): Verify calls to .DEFERRED_INIT.
>>> * tree-sra.c (generate_subtree_deferred_init): New function.
>>> (sra_modify_deferred_init): Likewise.
>>> (sra_modify_function_body): Handle calls to DEFERRED_INIT specially.
>>> * tree-ssa-structalias.c (find_func_aliases_for_call): Likewise.
>>> * tree-ssa-uninit.c (warn_uninit): Handle calls to DEFERRED_INIT
>>> specially.
>>> (check_defs): Likewise.
>>> (warn_uninitialized_vars): Likewise.
>>> * tree-ssa.c (ssa_undefined_value_p): Likewise.
>>>
>>> gcc/c-family/ChangeLog:
>>>
>>> 2021-07-23 qing zhao <qing.zhao@oracle.com>
>>>
>>> * c-attribs.c (handle_uninitialized_attribute): New function.
>>> (c_common_attribute_table): Add "uninitialized" attribute.
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