YJIT: add stats to keep track of when branch direction is known (#7544)

This measures the impact of changes made by @jhawthorn last year.

yjit.rb

@@ -272,6 +272,10 @@ module RubyVM::YJIT
       $stderr.puts "block_next_count:      " + format_number(13, stats[:block_next_count])
       $stderr.puts "defer_count:           " + format_number(13, stats[:defer_count])
       $stderr.puts "defer_empty_count:     " + format_number(13, stats[:defer_empty_count])
+
+      $stderr.puts "branch_insn_count:     " + format_number(13, stats[:branch_insn_count])
+      $stderr.puts "branch_known_count:    " + format_number_pct(13, stats[:branch_known_count], stats[:branch_insn_count])
+
       $stderr.puts "freed_iseq_count:      " + format_number(13, stats[:freed_iseq_count])
       $stderr.puts "invalidation_count:    " + format_number(13, stats[:invalidation_count])
       $stderr.puts "constant_state_bumps:  " + format_number(13, stats[:constant_state_bumps])

yjit/src/codegen.rs

@@ -3577,9 +3577,12 @@ fn gen_branchif(
     let val_type = ctx.get_opnd_type(StackOpnd(0));
     let val_opnd = ctx.stack_pop(1);
 
+    incr_counter!(branch_insn_count);
+
     if let Some(result) = val_type.known_truthy() {
         let target = if result { jump_block } else { next_block };
         gen_direct_jump(jit, ctx, target, asm);
+        incr_counter!(branch_known_count);
     } else {
         asm.test(val_opnd, Opnd::Imm(!Qnil.as_i64()));
 
@@ -3628,9 +3631,12 @@ fn gen_branchunless(
     let val_type = ctx.get_opnd_type(StackOpnd(0));
     let val_opnd = ctx.stack_pop(1);
 
+    incr_counter!(branch_insn_count);
+
     if let Some(result) = val_type.known_truthy() {
         let target = if result { next_block } else { jump_block };
         gen_direct_jump(jit, ctx, target, asm);
+        incr_counter!(branch_known_count);
     } else {
         // Test if any bit (outside of the Qnil bit) is on
         // See RB_TEST()
@@ -3682,9 +3688,12 @@ fn gen_branchnil(
     let val_type = ctx.get_opnd_type(StackOpnd(0));
     let val_opnd = ctx.stack_pop(1);
 
+    incr_counter!(branch_insn_count);
+
     if let Some(result) = val_type.known_nil() {
         let target = if result { jump_block } else { next_block };
         gen_direct_jump(jit, ctx, target, asm);
+        incr_counter!(branch_known_count);
     } else {
         // Test if the value is Qnil
         asm.cmp(val_opnd, Opnd::UImm(Qnil.into()));

yjit/src/stats.rs

@@ -324,6 +324,9 @@ make_counters! {
     block_next_count,
     defer_count,
     defer_empty_count,
+    branch_insn_count,
+    branch_known_count,
+
     freed_iseq_count,
 
     exit_from_branch_stub,