address partial review

Author: cocolato

Python/optimizer.c

@@ -599,8 +599,9 @@ add_to_trace(
 /* Branch penalty: 0 if fully biased, FITNESS_BRANCH_BALANCED if 50/50,
  * 2*FITNESS_BRANCH_BALANCED if fully against the traced direction. */
 static inline int
-compute_branch_penalty(uint16_t history, bool branch_taken)
+compute_branch_penalty(uint16_t history)
 {
+    bool branch_taken = history & 1;
     int taken_count = _Py_popcount32((uint32_t)history);
     int on_trace_count = branch_taken ? taken_count : 16 - taken_count;
     int off_trace = 16 - on_trace_count;
@@ -811,10 +812,8 @@ _PyJit_translate_single_bytecode_to_trace(
         goto done;
     }
 
-    // Snapshot the buffer before reserving tail slots. The later charge
-    // includes both emitted uops and capacity reserved for exits/deopts/errors.
+    // Snapshot the buffer position before emitting uops for this bytecode.
     _PyUOpInstruction *next_before = trace->next;
-    _PyUOpInstruction *end_before = trace->end;
 
     // One for possible _DEOPT, one because _CHECK_VALIDITY itself might _DEOPT
     trace->end -= 2;
@@ -864,7 +863,7 @@ _PyJit_translate_single_bytecode_to_trace(
             assert(jump_happened ? (next_instr == computed_jump_instr) : (next_instr == computed_next_instr));
             uint32_t uopcode = BRANCH_TO_GUARD[opcode - POP_JUMP_IF_FALSE][jump_happened];
             ADD_TO_TRACE(uopcode, 0, 0, INSTR_IP(jump_happened ? computed_next_instr : computed_jump_instr, old_code));
-            int bp = compute_branch_penalty(target_instr[1].cache, jump_happened);
+            int bp = compute_branch_penalty(target_instr[1].cache);
             tracer->translator_state.fitness -= bp;
             DPRINTF(3, "  branch penalty: -%d (history=0x%04x, taken=%d) -> fitness=%d\n",
                     bp, target_instr[1].cache, jump_happened,
@@ -1057,16 +1056,12 @@ _PyJit_translate_single_bytecode_to_trace(
         ADD_TO_TRACE(_JUMP_TO_TOP, 0, 0, 0);
         goto done;
     }
-    // Charge fitness by trace-buffer capacity consumed for this bytecode,
-    // including both emitted uops and tail reservations.
+    // Charge fitness by the number of uops actually emitted for this bytecode.
     {
-        int32_t slots_fwd = (int32_t)(trace->next - next_before);
-        int32_t slots_rev = (int32_t)(end_before - trace->end);
-        int32_t slots_used = slots_fwd + slots_rev;
+        int32_t slots_used = (int32_t)(trace->next - next_before);
         tracer->translator_state.fitness -= slots_used;
-        DPRINTF(3, "  per-insn cost: -%d (fwd=%d, rev=%d) -> fitness=%d\n",
-                slots_used, slots_fwd, slots_rev,
-                tracer->translator_state.fitness);
+        DPRINTF(3, "  per-insn cost: -%d -> fitness=%d\n",
+                slots_used, tracer->translator_state.fitness);
     }
     DPRINTF(2, "Trace continuing (fitness=%d)\n", tracer->translator_state.fitness);
     return 1;