gh-138946: Make binarysort adaptative

Misc/NEWS.d/next/Core_and_Builtins/2025-09-25-23-26-15.gh-issue-138946.uN03eR.rst

@@ -0,0 +1 @@
+Make binarysort adaptative. This improve sorting() performance by reducing the amount of comparisons of already sorted intervals.

Objects/listobject.c

@@ -1829,6 +1829,7 @@ binarysort(MergeState *ms, const sortslice *ss, Py_ssize_t n, Py_ssize_t ok)
     }
 #else // binary insertion sort
     Py_ssize_t L, R;
+    M = ok - 1;  // Start with the element close to the pivot
     for (; ok < n; ++ok) {
         /* set L to where a[ok] belongs */
         L = 0;
@@ -1841,14 +1842,14 @@ binarysort(MergeState *ms, const sortslice *ss, Py_ssize_t n, Py_ssize_t ok)
          */
         assert(L < R);
         do {
-            /* don't do silly ;-) things to prevent overflow when finding
-               the midpoint; L and R are very far from filling a Py_ssize_t */
-            M = (L + R) >> 1;
 #if 1 // straightforward, but highly unpredictable branch on random data
             IFLT(pivot, a[M])
                 R = M;
             else
                 L = M + 1;
+            /* don't do silly ;-) things to prevent overflow when finding
+               the midpoint; L and R are very far from filling a Py_ssize_t */
+            M = (L + R) >> 1;
 #else
             /* Try to get compiler to generate conditional move instructions
                instead. Works fine, but leaving it disabled for now because