From ba4f73bca19c586a1cb338b92bcd31573dbe9159 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 21 Jun 2019 00:51:29 +0900
Subject: [PATCH 1/2] bpo-37348: optimize PyUnicode_FromString for ASCII

---
 Objects/unicodeobject.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 4f8362590595cd..735ddfd6970421 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -2163,12 +2163,27 @@ PyUnicode_FromStringAndSize(const char *u, Py_ssize_t size)
 PyObject *
 PyUnicode_FromString(const char *u)
 {
-    size_t size = strlen(u);
-    if (size > PY_SSIZE_T_MAX) {
-        PyErr_SetString(PyExc_OverflowError, "input too long");
-        return NULL;
+    /* Most calls of PyUnicode_FromString is for short ASCII string.
+     * So we optimize this function for them.
+     */
+    size_t len = 0;
+    int is_ascii = 1;
+
+    while (u[len] != '\0') {
+        if (u[len] > 127) {
+            is_ascii = 0;
+        }
+        len++;
+        if (len > PY_SSIZE_T_MAX) {
+            PyErr_SetString(PyExc_OverflowError, "input too long");
+            return NULL;
+        }
     }
-    return PyUnicode_DecodeUTF8Stateful(u, (Py_ssize_t)size, NULL, NULL);
+
+    if (is_ascii) {
+        return _PyUnicode_FromASCII(u, (Py_ssize_t)len);
+    }
+    return PyUnicode_DecodeUTF8Stateful(u, (Py_ssize_t)len, NULL, NULL);
 }
 
 PyObject *
@@ -15303,8 +15318,9 @@ PyObject *
 PyUnicode_InternFromString(const char *cp)
 {
     PyObject *s = PyUnicode_FromString(cp);
-    if (s == NULL)
+    if (s == NULL) {
         return NULL;
+    }
     PyUnicode_InternInPlace(&s);
     return s;
 }

From 240310c62e927137fec734736c02ecd96eca2f04 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 21 Jun 2019 00:59:00 +0900
Subject: [PATCH 2/2] add news fragment

---
 .../Core and Builtins/2019-06-21-00-58-57.bpo-37348.PfJkWc.rst   | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2019-06-21-00-58-57.bpo-37348.PfJkWc.rst

diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-06-21-00-58-57.bpo-37348.PfJkWc.rst b/Misc/NEWS.d/next/Core and Builtins/2019-06-21-00-58-57.bpo-37348.PfJkWc.rst
new file mode 100644
index 00000000000000..3ed874d8a4c22d
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-06-21-00-58-57.bpo-37348.PfJkWc.rst	
@@ -0,0 +1 @@
+Optimized ``PyUnicode_GetString`` for short ASCII strings.