From 4f290ee246457aec1d7f6d0246fcf8895d23b9ff Mon Sep 17 00:00:00 2001
From: Torsten <torsten@rubydesign.fi>
Date: Wed, 18 Mar 2020 17:50:22 +0200
Subject: [PATCH] basic liveliness for allocator

---
 lib/risc/standard_allocator.rb        | 23 +++++++++++++++++++++++
 test/risc/test_standard_allocator.rb  |  7 +++++++
 test/risc/test_standard_allocator1.rb | 22 ++++++++++++++++++++++
 test/support/compiling.rb             |  2 +-
 4 files changed, 53 insertions(+), 1 deletion(-)
 create mode 100644 test/risc/test_standard_allocator1.rb

diff --git a/lib/risc/standard_allocator.rb b/lib/risc/standard_allocator.rb
index 01f4f218..ff38a331 100644
--- a/lib/risc/standard_allocator.rb
+++ b/lib/risc/standard_allocator.rb
@@ -13,6 +13,7 @@ module Risc
       @compiler = compiler
       @platform = platform
       @used_regs = {}
+      @release_points = Hash.new( [] )
       @reg_names = (0 ... platform.num_registers).collect{|i| "r#{i-1}".to_sym }
     end
     attr_reader :used_regs , :compiler , :platform , :reg_names
@@ -23,7 +24,29 @@ module Risc
     # Ie on arm register names are r0 .. . r15 , so it keeps a list of unused
     # regs and frees regs according to live ranges
     def allocate_regs
+      determine_liveness
+    end
 
+    # determines when registers can be freed
+    #
+    # this is done by walking the instructions backwards and saving the first
+    # occurence of a register name. (The last, as we walk backwards)
+    def determine_liveness
+      walk_and_mark(@compiler.risc_instructions)
+    end
+
+    # First walk down, and on the way up mark register occurences, unless they
+    # have been marked already
+    def walk_and_mark(instruction)
+      released = []
+      released = walk_and_mark(instruction.next) if instruction.next
+      #puts instruction.class.name
+      instruction.register_names.each do |name|
+        next if released.include?(name)
+        @release_points[instruction] << name
+        released << name
+      end
+      released
     end
 
     def used_regs_empty?
diff --git a/test/risc/test_standard_allocator.rb b/test/risc/test_standard_allocator.rb
index 76dd5906..16fbb5af 100644
--- a/test/risc/test_standard_allocator.rb
+++ b/test/risc/test_standard_allocator.rb
@@ -26,6 +26,13 @@ module Risc
     def test_platform
       assert_equal Arm::ArmPlatform , @allocator.platform.class
     end
+    def test_allocate_runs
+      assert @allocator.allocate_regs
+    end
+    def test_live
+      live = @allocator.determine_liveness
+      assert_equal 0 , live.length
+    end
     def test_add_ok
       assert_equal RegisterValue, @allocator.use_reg(tmp_reg).class
     end
diff --git a/test/risc/test_standard_allocator1.rb b/test/risc/test_standard_allocator1.rb
new file mode 100644
index 00000000..c34d8293
--- /dev/null
+++ b/test/risc/test_standard_allocator1.rb
@@ -0,0 +1,22 @@
+require_relative "../helper"
+
+module Risc
+  class TestStandardAllocator1 < MiniTest::Test
+    include SlotMachineCompile
+    def setup
+      coll = compile_slot( "class Space ; def main(); main{return 'Ho'};return 'Hi'; end; end;")
+      @compiler = coll.to_risc.method_compilers
+      @allocator = Platform.for(:arm).allocator(@compiler)
+    end
+    def test_main
+      assert_equal :main , @compiler.callable.name
+    end
+    def test_allocate_runs
+      assert @allocator.allocate_regs
+    end
+    def test_live_length
+      live = @allocator.determine_liveness
+      assert_equal 10 , live.length
+    end
+  end
+end
diff --git a/test/support/compiling.rb b/test/support/compiling.rb
index a4c8ba9f..483de819 100644
--- a/test/support/compiling.rb
+++ b/test/support/compiling.rb
@@ -4,7 +4,7 @@ module ScopeHelper
 
   def compiler_with_main(options = {})
     compiler = RubyX::RubyXCompiler.new(RubyX.default_test_options.merge(options))
-    compiler.ruby_to_sol( in_Space( as_main("return")) )
+    compiler.ruby_to_sol( as_main("return 5") )
     compiler
   end
   def in_Test(statements)