[gcc r13-1586] [RFA] Improve initialization of objects when the initializer has trailing zeros.

[Jeff Law <law@gcc.gnu.org>]

https://gcc.gnu.org/g:46dc26fdfbf3e64f82188e21aa6a13ec23108e8e

commit r13-1586-g46dc26fdfbf3e64f82188e21aa6a13ec23108e8e
Author: Jeff Law <jeffreyalaw@gmail.com>
Date:   Sat Jul 9 11:11:00 2022 -0400

    [RFA] Improve initialization of objects when the initializer has trailing zeros.
    
    gcc/
    
            * 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:
---
 gcc/expr.cc | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/gcc/expr.cc b/gcc/expr.cc
index eb280e6cac3..f9753d48245 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -6088,6 +6088,17 @@ 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;