Skip invalidation for trace_ insns

Merged: https://github.com/ruby/ruby/pull/7448

lib/ruby_vm/mjit/block.rb

@@ -4,6 +4,7 @@ class RubyVM::MJIT::Block < Struct.new(
   :start_addr,  # @param [Integer] Starting address of this block's JIT code
   :entry_exit,  # @param [Integer] Address of entry exit (optional)
   :incoming,    # @param [Array<RubyVM::MJIT::BranchStub>] Incoming branches
+  :invalidated, # @param [TrueClass,FalseClass] true if already invalidated
 )
-  def initialize(incoming: [], **) = super
+  def initialize(incoming: [], invalidated: false, **) = super
 end

lib/ruby_vm/mjit/compiler.rb

@@ -203,6 +203,12 @@ module RubyVM::MJIT
           break
         when CantCompile
           @exit_compiler.compile_side_exit(jit.pc, ctx, asm)
+
+          # If this is the first instruction, this block never needs to be invalidated.
+          if block.pc == iseq.body.iseq_encoded.to_i + index * C.VALUE.size
+            block.invalidated = true
+          end
+
           break
         else
           raise "compiling #{insn.name} returned unexpected status: #{status.inspect}"
@@ -224,12 +230,15 @@ module RubyVM::MJIT
       remove_block(iseq, block)
 
       # Invalidate the block with entry exit
+      unless block.invalidated
         @cb.with_write_addr(block.start_addr) do
           asm = Assembler.new
           asm.comment('invalidate_block')
           asm.jmp(block.entry_exit)
           @cb.write(asm)
         end
+        block.invalidated = true
+      end
 
       # Re-stub incoming branches
       block.incoming.each do |branch_stub|