From f3ee11fca513a8015a8984520c8749fb599703a3 Mon Sep 17 00:00:00 2001
From: Torsten Ruger <torsten@villataika.fi>
Date: Sun, 21 Jun 2015 17:25:27 +0300
Subject: [PATCH] simple set optimisation

the price of having simple code (generation) is that
it is sometimes stupid code that gets generated
Filter some of the really daft stuff out
---
 lib/virtual/passes/set_optimisation.rb | 19 +++++++++++++++++++
 test/virtual/test_hello.rb             |  2 +-
 2 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 lib/virtual/passes/set_optimisation.rb

diff --git a/lib/virtual/passes/set_optimisation.rb b/lib/virtual/passes/set_optimisation.rb
new file mode 100644
index 00000000..1fcfe34d
--- /dev/null
+++ b/lib/virtual/passes/set_optimisation.rb
@@ -0,0 +1,19 @@
+module Virtual
+
+  class SetOptimisation
+    def run block
+      block.codes.dup.each_with_index do |code , i|
+        next unless code.is_a? Virtual::Set
+        next_code = block.codes[i+1]
+        next unless next_code.is_a? Virtual::Set
+        next unless code.to == next_code.from
+        # TODO: a correct implementation would have to check that the code.to
+        #       is not used in further blocks, before being assigned to
+        new_code = Virtual::Set.new(code.from , next_code.to )
+        block.replace(code , [new_code] )
+        block.replace(next_code , [] )
+      end
+    end
+  end
+  Virtual.machine.add_pass "Virtual::SetOptimisation"
+end
diff --git a/test/virtual/test_hello.rb b/test/virtual/test_hello.rb
index 6deccc63..db7e5bc0 100644
--- a/test/virtual/test_hello.rb
+++ b/test/virtual/test_hello.rb
@@ -6,7 +6,7 @@ class HelloTest < MiniTest::Test
   def check
     machine = Virtual::Machine.boot
     expressions = machine.compile_main @string_input
-    output_at = Virtual::Machine::FIRST_PASS
+    output_at = "Virtual::SetOptimisation"
     #{}"Register::CallImplementation"
     machine.run_before output_at
     puts Sof.write(machine.space)