gh-145629: Expand block inlining to enable LOAD_FAST_BORROW optimization for return ternary expressions

Lib/test/test_peepholer.py

@@ -1129,6 +1129,14 @@ def f(self):
             print(ExecError)
         self.assertInBytecode(f, "LOAD_FAST_BORROW", "self")
 
+    def test_ternary_expression_uses_load_fast_borrow(self):
+        def f(a, b):
+            return a if a < b else b
+
+        self.assertNotInBytecode(f, "LOAD_FAST")
+        self.assertInBytecode(f, "LOAD_FAST_BORROW", "a")
+        self.assertInBytecode(f, "LOAD_FAST_BORROW", "b")
+
 class DirectCfgOptimizerTests(CfgOptimizationTestCase):
 
     def cfg_optimization_test(self, insts, expected_insts,

Misc/NEWS.d/next/Core_and_Builtins/2026-03-27-04-16-08.gh-issue-145629.eLFhwn.rst

@@ -0,0 +1 @@
+Fix missed ``LOAD_FAST_BORROW`` optimization for ternary expressions by improving basic block inlining during the compiler's control flow graph optimization phase.

Python/flowgraph.c

@@ -1218,6 +1218,7 @@ basicblock_has_no_lineno(basicblock *b) {
 /* If this block ends with an unconditional jump to a small exit block or
  * a block that has no line numbers (and no fallthrough), then
  * remove the jump and extend this block with the target.
+ * Also handles the case where a block falls through to a small exit block.
  * Returns 1 if extended, 0 if no change, and -1 on error.
  */
 static int
@@ -1227,6 +1228,15 @@ basicblock_inline_small_or_no_lineno_blocks(basicblock *bb) {
         return 0;
     }
     if (!IS_UNCONDITIONAL_JUMP_OPCODE(last->i_opcode)) {
+        // If the block ends with a fallthrough to a small exit block, inline it.
+        if (BB_HAS_FALLTHROUGH(bb) && bb->b_next != NULL && !is_jump(last)) {
+            basicblock *next = bb->b_next;
+            if (basicblock_exits_scope(next) && next->b_iused <= MAX_COPY_SIZE) {
+                RETURN_IF_ERROR(basicblock_append_instructions(bb, next));
+                next->b_predecessors--;
+                return 1;
+            }
+        }
         return 0;
     }
     basicblock *target = last->i_target;