From 5f12875729948c2048a4b88678f5293fc7fc805f Mon Sep 17 00:00:00 2001
From: Jean Privat <jean@pryen.org>
Date: Mon, 27 Jul 2009 02:59:57 -0400
Subject: [PATCH] icode: discard unused pure ICode expressions

Up to now, only unused IMove expressions where discarded.
So we also distinguish pure ICode from non pure ICode.

Signed-off-by: Jean Privat <jean@pryen.org>
---
 src/compiling/compiling_icode.nit |    4 +++-
 src/icode/icode_base.nit          |   19 +++++++++++++++++++
 src/icode/icode_builder.nit       |    2 ++
 src/icode/icode_tools.nit         |    4 +++-
 4 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/compiling/compiling_icode.nit b/src/compiling/compiling_icode.nit
index 847280b..97514ac 100644
--- a/src/compiling/compiling_icode.nit
+++ b/src/compiling/compiling_icode.nit
@@ -358,7 +358,9 @@ redef class ICode
 		if r != null and r.slot_index != null then
 			assert s != null
 			v.add_assignment(v.register(r), s)
-		else if s != null and not self isa IMove then
+		else if s != null and not is_pure then
+			# ICode with side effects must be evaluated
+			# even if the result is not wanted
 			v.add_instr(s + ";")
 		end
 	end
diff --git a/src/icode/icode_base.nit b/src/icode/icode_base.nit
index f46ff5b..6a822e3 100644
--- a/src/icode/icode_base.nit
+++ b/src/icode/icode_base.nit
@@ -88,6 +88,9 @@ abstract class ICode
 
 	# The location of the icode (if any)
 	readable writable var _location: nullable Location = null
+
+	# Is the icode side effect free?
+	fun is_pure: Bool do return false
 end
 
 # An icode that uses no registers (no args)
@@ -274,6 +277,8 @@ special ICodeN
 		super(e)
 		_code = c
 	end
+
+	redef readable writable var _is_pure: Bool = false
 end
 
 # A register assigment
@@ -286,6 +291,8 @@ special ICode1
 		super(e)
 		_result = r
 	end
+
+	redef fun is_pure do return true
 end
 
 # An attribute read access
@@ -300,6 +307,8 @@ special ICode1
 		super(r)
 		_property = p
 	end
+
+	redef fun is_pure do return true
 end
 
 # An attribute assignment
@@ -329,6 +338,8 @@ special ICode1
 		super(r)
 		_property = p
 	end
+
+	redef fun is_pure do return true
 end
 
 # A type check
@@ -343,6 +354,8 @@ special ICode1
 		super(e)
 		_stype = t
 	end
+
+	redef fun is_pure do return true
 end
 
 # The 'is' operator
@@ -353,6 +366,8 @@ special ICode2
 	do
 		super
 	end
+
+	redef fun is_pure do return true
 end
 
 # The unary 'not' operation
@@ -363,6 +378,8 @@ special ICode1
 	do
 		super
 	end
+
+	redef fun is_pure do return true
 end
 
 # Evaluate body once them return the same value again and again
@@ -383,6 +400,8 @@ special ICode0
 	do
 		_closure_decl = c
 	end
+
+	redef fun is_pure do return true
 end
 
 #################################################
diff --git a/src/icode/icode_builder.nit b/src/icode/icode_builder.nit
index dbb26bd..88c3796 100644
--- a/src/icode/icode_builder.nit
+++ b/src/icode/icode_builder.nit
@@ -169,6 +169,7 @@ class ICodeBuilder
 	fun lit_true_reg: IRegister
 	do
 		var e = new INative("TAG_Bool(true)", null)
+		e.is_pure = true
 		return expr(e, module.type_bool)
 	end
 
@@ -176,6 +177,7 @@ class ICodeBuilder
 	fun lit_false_reg: IRegister
 	do
 		var e = new INative("TAG_Bool(false)", null)
+		e.is_pure = true
 		return expr(e, module.type_bool)
 	end
 
diff --git a/src/icode/icode_tools.nit b/src/icode/icode_tools.nit
index efdc0b7..5186233 100644
--- a/src/icode/icode_tools.nit
+++ b/src/icode/icode_tools.nit
@@ -258,7 +258,9 @@ end
 redef class INative
 	redef fun inner_dup_with(d)
 	do
-		return new INative(code, d.dup_iregs(exprs))
+		var c2 = new INative(code, d.dup_iregs(exprs))
+		c2.is_pure = is_pure
+		return c2
 	end
 end
 
-- 
1.7.9.5