Re: [RFA] Improve initialization of objects when the initializer has trailing zeros.
On Thu, Jul 7, 2022 at 4:46 PM Jeff Law via Gcc-patches wrote: > > 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? OK. Thanks, Richard. > Jeff >
Re: [RFA] Improve initialization of objects when the initializer has trailing zeros.
On 2022/07/07 23:46, Jeff Law wrote: > 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. Thank you for understanding what I mean... > 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. and offering good explanation. > 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. LGTM and of course it resolves the beginning of the first place (https://gcc.gnu.org/pipermail/gcc-patches/2022-May/595685.html). > > OK for the trunk? > > Jeff >
[RFA] Improve initialization of objects when the initializer has trailing zeros.
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
* 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;
