From: Jeff Law <jeffreyalaw@gmail.com>
To: 'GCC Patches' <gcc-patches@gcc.gnu.org>
Subject: [RFA] Improve initialization of objects when the initializer has trailing zeros.
Date: Thu, 7 Jul 2022 08:46:16 -0600 [thread overview]
Message-ID: <446ea3de-5486-8756-47f1-7822d79c5d75@gmail.com> (raw)
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This is an update to a patch originally posted by Takayuki Suwa a few
months ago.
When we initialize an array from a STRING_CST we perform the
initialization in two steps. The first step copies the STRING_CST to
the destination. The second step uses clear_storage to initialize
storage in the array beyond TREE_STRING_LENGTH of the initializer.
Takayuki's patch added a special case when the STRING_CST itself was all
zeros which would avoid the copy from the STRING_CST and instead do all
the initialization via clear_storage which is clearly more runtime
efficient.
Richie had the suggestion that instead of special casing when the entire
STRING_CST was NULs to instead identify when the tail of the STRING_CST
was NULs. That's more general and handles Takayuki's case as well.
Bootstrapped and regression tested on x86_64-linux-gnu. Given I rewrote
Takayuki's patch I think it needs someone else to review rather than
self-approving.
OK for the trunk?
Jeff
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* expr.cc (store_expr): Identify trailing NULs in a STRING_CST
initializer and use clear_storage rather than copying the
NULs to the destination array.
diff --git a/gcc/expr.cc b/gcc/expr.cc
index 62297379ec9..f94d46b969c 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -6087,6 +6087,17 @@ store_expr (tree exp, rtx target, int call_param_p,
}
str_copy_len = TREE_STRING_LENGTH (str);
+
+ /* Trailing NUL bytes in EXP will be handled by the call to
+ clear_storage, which is more efficient than copying them from
+ the STRING_CST, so trim those from STR_COPY_LEN. */
+ while (str_copy_len)
+ {
+ if (TREE_STRING_POINTER (str)[str_copy_len - 1])
+ break;
+ str_copy_len--;
+ }
+
if ((STORE_MAX_PIECES & (STORE_MAX_PIECES - 1)) == 0)
{
str_copy_len += STORE_MAX_PIECES - 1;
next reply other threads:[~2022-07-07 14:46 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-07 14:46 Jeff Law [this message]
2022-07-08 0:06 ` Takayuki 'January June' Suwa
2022-07-08 7:11 ` Richard Biener
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