* [PATCH] expr.cc: Optimize if char array initialization consists of all zeros
@ 2022-05-31 3:35 Takayuki 'January June' Suwa
2022-06-01 8:57 ` Richard Biener
2022-06-26 19:34 ` Jeff Law
0 siblings, 2 replies; 3+ messages in thread
From: Takayuki 'January June' Suwa @ 2022-05-31 3:35 UTC (permalink / raw)
To: GCC Patches
Hi all,
In some targets, initialization code for char array may be split into two
parts even if the initialization consists of all zeros:
/* example */
extern void foo(char*);
void test(void) {
char a[256] = { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
foo(a);
}
;; Xtensa (xtensa-lx106)
.LC0:
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.zero 246
test:
movi a9, 0x110
sub sp, sp, a9
l32r a3, .LC1
movi.n a4, 0xa
mov.n a2, sp
s32i a0, sp, 268
call0 memcpy
movi a4, 0xf6
movi.n a3, 0
addi.n a2, sp, 10
call0 memset
mov.n a2, sp
call0 foo
l32i a0, sp, 268
movi a9, 0x110
add.n sp, sp, a9
ret.n
;; H8/300 (-mh -mint32)
.LC0:
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.string ""
.zero 246
_test:
sub.l #256,er7
sub.l er2,er2
add.b #10,r2l
mov.l #.LC0,er1
mov.l er7,er0
jsr @_memcpy
sub.l er2,er2
add.b #246,r2l
sub.l er1,er1
sub.l er0,er0
add.b #10,r0l
add.l er7,er0
jsr @_memset
mov.l er7,er0
jsr @_foo
add.l #256,er7
rts
i386 target (both 32 and 64bit) does not show such behavior.
gcc/ChangeLog:
* expr.cc (store_expr): Add check if the initialization content
consists of all zeros.
---
gcc/expr.cc | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/gcc/expr.cc b/gcc/expr.cc
index 7197996cec7..f94310dc7b9 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -6015,6 +6015,7 @@ store_expr (tree exp, rtx target, int call_param_p,
rtx dest_mem;
tree str = TREE_CODE (exp) == STRING_CST
? exp : TREE_OPERAND (TREE_OPERAND (exp, 0), 0);
+ char ch;
exp_len = int_expr_size (exp);
if (exp_len <= 0)
@@ -6032,6 +6033,12 @@ store_expr (tree exp, rtx target, int call_param_p,
}
str_copy_len = TREE_STRING_LENGTH (str);
+ /* If str contains only zeroes, no need to store to target. */
+ ch = 0;
+ for (HOST_WIDE_INT i = 0; i < str_copy_len; ++i)
+ ch |= TREE_STRING_POINTER (str)[i];
+ if (ch == 0)
+ str_copy_len = 0;
if ((STORE_MAX_PIECES & (STORE_MAX_PIECES - 1)) == 0)
{
str_copy_len += STORE_MAX_PIECES - 1;
--
2.20.1
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] expr.cc: Optimize if char array initialization consists of all zeros
2022-05-31 3:35 [PATCH] expr.cc: Optimize if char array initialization consists of all zeros Takayuki 'January June' Suwa
@ 2022-06-01 8:57 ` Richard Biener
2022-06-26 19:34 ` Jeff Law
1 sibling, 0 replies; 3+ messages in thread
From: Richard Biener @ 2022-06-01 8:57 UTC (permalink / raw)
To: Takayuki 'January June' Suwa; +Cc: GCC Patches
On Tue, May 31, 2022 at 5:37 AM Takayuki 'January June' Suwa via
Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>
> Hi all,
>
> In some targets, initialization code for char array may be split into two
> parts even if the initialization consists of all zeros:
>
> /* example */
> extern void foo(char*);
> void test(void) {
> char a[256] = { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
> foo(a);
> }
>
> ;; Xtensa (xtensa-lx106)
> .LC0:
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .zero 246
> test:
> movi a9, 0x110
> sub sp, sp, a9
> l32r a3, .LC1
> movi.n a4, 0xa
> mov.n a2, sp
> s32i a0, sp, 268
> call0 memcpy
> movi a4, 0xf6
> movi.n a3, 0
> addi.n a2, sp, 10
> call0 memset
> mov.n a2, sp
> call0 foo
> l32i a0, sp, 268
> movi a9, 0x110
> add.n sp, sp, a9
> ret.n
>
> ;; H8/300 (-mh -mint32)
> .LC0:
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .zero 246
> _test:
> sub.l #256,er7
> sub.l er2,er2
> add.b #10,r2l
> mov.l #.LC0,er1
> mov.l er7,er0
> jsr @_memcpy
> sub.l er2,er2
> add.b #246,r2l
> sub.l er1,er1
> sub.l er0,er0
> add.b #10,r0l
> add.l er7,er0
> jsr @_memset
> mov.l er7,er0
> jsr @_foo
> add.l #256,er7
> rts
>
> i386 target (both 32 and 64bit) does not show such behavior.
>
> gcc/ChangeLog:
>
> * expr.cc (store_expr): Add check if the initialization content
> consists of all zeros.
> ---
> gcc/expr.cc | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/gcc/expr.cc b/gcc/expr.cc
> index 7197996cec7..f94310dc7b9 100644
> --- a/gcc/expr.cc
> +++ b/gcc/expr.cc
> @@ -6015,6 +6015,7 @@ store_expr (tree exp, rtx target, int call_param_p,
> rtx dest_mem;
> tree str = TREE_CODE (exp) == STRING_CST
> ? exp : TREE_OPERAND (TREE_OPERAND (exp, 0), 0);
> + char ch;
>
> exp_len = int_expr_size (exp);
> if (exp_len <= 0)
> @@ -6032,6 +6033,12 @@ store_expr (tree exp, rtx target, int call_param_p,
> }
>
> str_copy_len = TREE_STRING_LENGTH (str);
> + /* If str contains only zeroes, no need to store to target. */
> + ch = 0;
> + for (HOST_WIDE_INT i = 0; i < str_copy_len; ++i)
> + ch |= TREE_STRING_POINTER (str)[i];
> + if (ch == 0)
> + str_copy_len = 0;
Not sure if I decipher the current code correctly but maybe we instead
want to prune str_copy_len from the end for trailing \0 bytes instead of
just special-casing all-zero initializers?
> if ((STORE_MAX_PIECES & (STORE_MAX_PIECES - 1)) == 0)
> {
> str_copy_len += STORE_MAX_PIECES - 1;
> --
> 2.20.1
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] expr.cc: Optimize if char array initialization consists of all zeros
2022-05-31 3:35 [PATCH] expr.cc: Optimize if char array initialization consists of all zeros Takayuki 'January June' Suwa
2022-06-01 8:57 ` Richard Biener
@ 2022-06-26 19:34 ` Jeff Law
1 sibling, 0 replies; 3+ messages in thread
From: Jeff Law @ 2022-06-26 19:34 UTC (permalink / raw)
To: gcc-patches
On 5/30/2022 9:35 PM, Takayuki 'January June' Suwa via Gcc-patches wrote:
> Hi all,
>
> In some targets, initialization code for char array may be split into two
> parts even if the initialization consists of all zeros:
>
> /* example */
> extern void foo(char*);
> void test(void) {
> char a[256] = { 0, 0, 0, 0, 0, 0, 0, 0, 0 };
> foo(a);
> }
>
> ;; Xtensa (xtensa-lx106)
> .LC0:
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .zero 246
> test:
> movi a9, 0x110
> sub sp, sp, a9
> l32r a3, .LC1
> movi.n a4, 0xa
> mov.n a2, sp
> s32i a0, sp, 268
> call0 memcpy
> movi a4, 0xf6
> movi.n a3, 0
> addi.n a2, sp, 10
> call0 memset
> mov.n a2, sp
> call0 foo
> l32i a0, sp, 268
> movi a9, 0x110
> add.n sp, sp, a9
> ret.n
>
> ;; H8/300 (-mh -mint32)
> .LC0:
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .string ""
> .zero 246
> _test:
> sub.l #256,er7
> sub.l er2,er2
> add.b #10,r2l
> mov.l #.LC0,er1
> mov.l er7,er0
> jsr @_memcpy
> sub.l er2,er2
> add.b #246,r2l
> sub.l er1,er1
> sub.l er0,er0
> add.b #10,r0l
> add.l er7,er0
> jsr @_memset
> mov.l er7,er0
> jsr @_foo
> add.l #256,er7
> rts
>
> i386 target (both 32 and 64bit) does not show such behavior.
>
> gcc/ChangeLog:
>
> * expr.cc (store_expr): Add check if the initialization content
> consists of all zeros.
It's not entirely clear what you're trying to accomplish. Is it the
.zero which allocates space in the .rodata you're trying to remove? If
so, it looks like that is already addressed on the trunk to me (I
checked H8 with and without optimization).
jeff
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-05-31 3:35 [PATCH] expr.cc: Optimize if char array initialization consists of all zeros Takayuki 'January June' Suwa
2022-06-01 8:57 ` Richard Biener
2022-06-26 19:34 ` Jeff Law
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