Mimimize the conditionals and the numer of ops inside the

mpaolini · mpaolini · commit fa52a8372571 · 2019-07-13T21:10:24.000+01:00
json.loads hot path.

This partially reverts the previous commit as we found out
the culprit wasn't the MOV but the strictness checks
diff --git a/Modules/_json.c b/Modules/_json.c
@@ -434,19 +434,20 @@ scanstring_unicode(PyObject *pystr, Py_ssize_t end, int strict, Py_ssize_t *next
     while (1) {
         /* Find the end of the string or the next escape */
         Py_UCS4 c = 0;
-        next = end;
-        /* This is a tight loop in a hot path so we try to avoid
-           MOV from the register variable into memory. See bpo-37587 */
-        for (Py_UCS4 c_in = 0; next < len; next++) {
-            c_in = PyUnicode_READ(kind, buf, next);
-            if (c_in == '"' || c_in == '\\') {
-                c = c_in;
+        Py_ssize_t invalid = -1;
+        for (next = end; next < len; next++) {
+            c = PyUnicode_READ(kind, buf, next);
+            if (c == '"' || c == '\\') {
                 break;
             }
-            else if (c_in <= 0x1f && strict) {
-                raise_errmsg("Invalid control character at", pystr, next);
-                goto bail;
-            }
+            /* Defer the strict error until outside this (hot) loop. */
+            /* See bpo-37587 */
+            if (c <= 0x1f && invalid < 0)
+              invalid = next;
+        }
+        if (strict && invalid >= 0) {
+            raise_errmsg("Invalid control character at", pystr, invalid);
+            goto bail;
         }
         if (!(c == '"' || c == '\\')) {
             raise_errmsg("Unterminated string starting at", pystr, begin);
