| Message ID | 446ea3de-5486-8756-47f1-7822d79c5d75@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | [RFA] Improve initialization of objects when the initializer has trailing zeros. | expand |
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 >
On Thu, Jul 7, 2022 at 4:46 PM Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org> 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 >
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;