Be less confident about jumps always/never taken

gvanrossum · Feb 20, 2024 · 2537f75 · 2537f75
1 parent c1583b1
commit 2537f75
Showing 1 changed file with 6 additions and 2 deletions.
diff --git a/Python/optimizer.c b/Python/optimizer.c
@@ -593,11 +593,15 @@ translate_bytecode_to_trace(
                 int counter = instr[1].cache;
                 int bitcount = _Py_popcount32(counter);
                 int jump_likely = bitcount > 8;
+                /* If bitcount is 8 (half the jumps were taken), adjust confidence by 50%.
+                   If it's 16 or 0 (all or none were taken), adjust by 10%
+                   (since the future is still somewhat uncertain).
+                   For values in between, adjust proportionally. */
                 if (jump_likely) {
-                    confidence = confidence * bitcount / 16;
+                    confidence = confidence * (bitcount + 2) / 20;
                 }
                 else {
-                    confidence = confidence * (16 - bitcount) / 16;
+                    confidence = confidence * (18 - bitcount) / 20;
                 }
                 uint32_t uopcode = BRANCH_TO_GUARD[opcode - POP_JUMP_IF_FALSE][jump_likely];
                 DPRINTF(2, "%s(%d): counter=%x, bitcount=%d, likely=%d, confidence=%d, uopcode=%s\n",