From: Qing Zhao <qing.zhao@oracle.com>
To: Richard Biener <rguenther@suse.de>
Cc: Martin Jambor <mjambor@suse.cz>, Jakub Jelinek <jakub@redhat.com>,
Kees Cook <keescook@chromium.org>,
Nick Alcock via Gcc-patches <gcc-patches@gcc.gnu.org>,
Richard Biener <richard.guenther@gmail.com>
Subject: Re: [patch][version 6] add -ftrivial-auto-var-init and variable attribute "uninitialized" to gcc
Date: Thu, 12 Aug 2021 19:24:18 +0000 [thread overview]
Message-ID: <517EA40B-9500-4090-8F03-B4A9CECC62F8@oracle.com> (raw)
In-Reply-To: <nycvar.YFH.7.76.2108091529330.11781@zhemvz.fhfr.qr>
Hi, Richard,
For RTL expansion of call to .DEFERRED_INIT, I changed my code per your suggestions like following:
======================
#define INIT_PATTERN_VALUE 0xFE
static void
expand_DEFERRED_INIT (internal_fn, gcall *stmt)
{
tree lhs = gimple_call_lhs (stmt);
tree var_size = gimple_call_arg (stmt, 0);
enum auto_init_type init_type
= (enum auto_init_type) TREE_INT_CST_LOW (gimple_call_arg (stmt, 1));
bool is_vla = (bool) TREE_INT_CST_LOW (gimple_call_arg (stmt, 2));
tree var_type = TREE_TYPE (lhs);
gcc_assert (init_type > AUTO_INIT_UNINITIALIZED);
if (is_vla || (!can_native_interpret_type_p (var_type)))
{
/* If this is a VLA or the type of the variable cannot be natively
interpreted, expand to a memset to initialize it. */
if (TREE_CODE (lhs) == SSA_NAME)
lhs = SSA_NAME_VAR (lhs);
tree var_addr = NULL_TREE;
if (is_vla)
var_addr = TREE_OPERAND (lhs, 0);
else
{
TREE_ADDRESSABLE (lhs) = 1;
var_addr = build_fold_addr_expr (lhs);
}
tree value = (init_type == AUTO_INIT_PATTERN) ?
build_int_cst (unsigned_char_type_node,
INIT_PATTERN_VALUE) :
build_zero_cst (unsigned_char_type_node);
tree m_call = build_call_expr (builtin_decl_implicit (BUILT_IN_MEMSET),
3, var_addr, value, var_size);
/* Expand this memset call. */
expand_builtin_memset (m_call, NULL_RTX, TYPE_MODE (var_type));
}
else
{
/* If this is not a VLA and the type of the variable can be natively
interpreted, expand to assignment to generate better code. */
tree pattern = NULL_TREE;
unsigned HOST_WIDE_INT total_bytes
= tree_to_uhwi (TYPE_SIZE_UNIT (var_type));
if (init_type == AUTO_INIT_PATTERN)
{
unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
memset (buf, INIT_PATTERN_VALUE, total_bytes);
pattern = native_interpret_expr (var_type, buf, total_bytes);
gcc_assert (pattern);
}
tree init = (init_type == AUTO_INIT_PATTERN) ?
pattern :
build_zero_cst (var_type);
expand_assignment (lhs, init, false);
}
}
===========================
Now, I used “can_native_interpret_type_p (var_type)” instead of “use_register_for_decl (lhs)” to decide
whether to use “memset” or use “assign” to expand this function.
However, this exposed an bug that is very hard to be addressed:
*******For the testing case: test suite/gcc.dg/uninit-I.c:
/* { dg-do compile } */
/* { dg-options "-O2 -Wuninitialized" } */
int sys_msgctl (void)
{
struct { int mode; } setbuf;
return setbuf.mode; /* { dg-warning "'setbuf\.mode' is used" } */
==
******the above auto var “setbuf” has “struct” type, which “can_native_interpret_type_p(var_type)” is false, therefore,
Expanding this .DEFERRED_INIT call went down the “memset” expansion route.
However, this structure type can be fitted into a register, therefore cannot be taken address anymore at this stage, even though I tried:
TREE_ADDRESSABLE (lhs) = 1;
var_addr = build_fold_addr_expr (lhs);
To create an address variable for it, the expansion still failed at expr.c: line 8412:
during RTL pass: expand
/home/opc/Work/GCC/latest-gcc/gcc/testsuite/gcc.dg/auto-init-uninit-I.c:6:24: internal compiler error: in expand_expr_addr_expr_1, at expr.c:8412
0xd04104 expand_expr_addr_expr_1
../../latest-gcc/gcc/expr.c:8412
0xd04a95 expand_expr_addr_expr
../../latest-gcc/gcc/expr.c:8525
0xd13592 expand_expr_real_1(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
../../latest-gcc/gcc/expr.c:11741
0xd05142 expand_expr_real(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
../../latest-gcc/gcc/expr.c:8713
0xaed1d3 expand_expr
../../latest-gcc/gcc/expr.h:301
0xaf0d89 get_memory_rtx
../../latest-gcc/gcc/builtins.c:1370
0xafb4fb expand_builtin_memset_args
../../latest-gcc/gcc/builtins.c:4102
0xafacde expand_builtin_memset(tree_node*, rtx_def*, machine_mode)
../../latest-gcc/gcc/builtins.c:3886
0xe97fb3 expand_DEFERRED_INIT
******That’s the major reason why I chose “use_register_for_decl(lhs)” to decide “memset” expansion or “assign” expansion, “memset” expansion
needs to take address of the variable, if the variable has been decided to fit into a register, then its address cannot taken anymore at this stage.
******using “can_native_interpret_type_p” did make the “pattern” generation part much cleaner and simpler, however, looks like it didn’t work correctly.
Based on this, I’d like to keep my previous implementation by using “use_register_for_decl” to decide whether to take “memset” expansion or “assign” expansion.
Therefore, I might still need to keep the “UGLY” implementation of generatting “pattern” constant for different types?
Let me know your opinion on this.
Thanks a lot for the help.
Qing
> On Aug 9, 2021, at 9:09 AM, Richard Biener <rguenther@suse.de> wrote:
>
> On Tue, 27 Jul 2021, Qing Zhao wrote:
>
> + created during gimplification phase. Refer to gimplify_vla_decl
> + for details. */
> + tree var_decl = (TREE_CODE (var) == SSA_NAME) ?
> + SSA_NAME_VAR (var) : var;
> + gcc_assert (DECL_HAS_VALUE_EXPR_P (var_decl));
> + gcc_assert (TREE_CODE (DECL_VALUE_EXPR (var_decl)) ==
> INDIRECT_REF);
> + /* Get the address of this vla variable. */
> + vlaaddr = TREE_OPERAND (DECL_VALUE_EXPR (var_decl), 0);
>
> err - isn't the address of the decl represented by the LHS
> regardless whether this is a VLA or not? Looking at DECL_VALUE_EXPR
> looks quite fragile since that's not sth data dependence honors.
> It looks you only partly gimplify the build init here? All
> DECL_VALUE_EXPRs should have been resolved.
>
> + if (is_vla || (!use_register_for_decl (var)))
> ...
> + else
> + {
> + /* If this variable is in a register, use expand_assignment might
> + generate better code. */
>
> you compute the patter initializer even when not needing it,
> that's wasteful. It's also quite ugly, IMHO you should
> use can_native_interpret_type_p (var_type) and native_interpret
> a char [] array initialized to the pattern and if
> !can_native_interpret_type_p () go the memset route.
next prev parent reply other threads:[~2021-08-12 19:24 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-27 3:26 Qing Zhao
2021-07-28 20:21 ` Kees Cook
2021-07-28 21:53 ` Qing Zhao
2021-08-09 14:09 ` Richard Biener
2021-08-09 16:38 ` Qing Zhao
2021-08-09 17:14 ` Richard Biener
2021-08-10 7:36 ` Richard Biener
2021-08-10 13:39 ` Qing Zhao
2021-08-10 14:16 ` Richard Biener
2021-08-10 15:02 ` Qing Zhao
2021-08-10 15:22 ` Richard Biener
2021-08-10 15:55 ` Qing Zhao
2021-08-10 20:16 ` Qing Zhao
2021-08-10 22:26 ` Qing Zhao
2021-08-11 7:02 ` Richard Biener
2021-08-11 13:33 ` Qing Zhao
2021-08-11 13:37 ` Richard Biener
2021-08-11 13:54 ` Qing Zhao
2021-08-11 13:58 ` Richard Biener
2021-08-11 14:00 ` Qing Zhao
2021-08-11 15:30 ` Qing Zhao
2021-08-11 15:53 ` Richard Biener
2021-08-11 16:22 ` Qing Zhao
2021-08-11 16:55 ` Richard Biener
2021-08-11 16:57 ` Qing Zhao
2021-08-11 20:30 ` Qing Zhao
2021-08-11 22:03 ` Qing Zhao
2021-08-16 7:12 ` Richard Biener
2021-08-16 14:48 ` Qing Zhao
2021-08-16 15:08 ` Richard Biener
2021-08-16 15:39 ` Qing Zhao
2021-08-16 7:11 ` Richard Biener
2021-08-16 16:48 ` Qing Zhao
2021-08-17 15:04 ` Qing Zhao
2021-08-17 20:40 ` Qing Zhao
2021-08-18 7:19 ` Richard Biener
2021-08-18 14:39 ` Qing Zhao
2021-08-11 9:02 ` Richard Sandiford
2021-08-11 13:44 ` Qing Zhao
2021-08-11 16:15 ` Richard Sandiford
2021-08-11 16:29 ` Qing Zhao
2021-08-12 19:24 ` Qing Zhao [this message]
2021-08-12 22:45 ` Qing Zhao
2021-08-16 7:40 ` Richard Biener
2021-08-16 15:45 ` Qing Zhao
2021-08-17 8:29 ` Richard Biener
2021-08-17 14:50 ` Qing Zhao
2021-08-17 16:08 ` Qing Zhao
2021-08-18 7:15 ` Richard Biener
2021-08-18 16:02 ` Qing Zhao
2021-08-19 9:00 ` Richard Biener
2021-08-19 13:54 ` Qing Zhao
2021-08-20 14:52 ` Qing Zhao
2021-08-23 13:55 ` Richard Biener
2021-09-02 17:24 ` Qing Zhao
2021-08-16 19:49 ` Qing Zhao
2021-08-17 8:43 ` Richard Biener
2021-08-17 14:03 ` Qing Zhao
2021-08-17 14:45 ` Richard Biener
2021-08-17 14:53 ` Qing Zhao
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