Codegen: inline constants

spec/compiler/codegen/const_spec.cr

@@ -380,4 +380,63 @@ describe "Codegen: const" do
       Foo.new.z
       )).to_i.should eq(42)
   end
+
+  it "inlines simple const" do
+    mod = codegen(%(
+      CONST = 1
+      CONST
+      ))
+
+    mod.to_s.should_not contain("CONST")
+  end
+
+  it "inlines enum value" do
+    mod = codegen(%(
+      enum Foo
+        CONST
+      end
+
+      Foo::CONST
+      ))
+
+    mod.to_s.should_not contain("CONST")
+  end
+
+  it "inlines const with math" do
+    mod = codegen(%(
+      CONST = (1 + 2) * 3
+      ))
+
+    mod.to_s.should_not contain("CONST")
+  end
+
+  it "inlines const referencing another const" do
+    mod = codegen(%(
+      OTHER = 1
+
+      CONST = OTHER
+      CONST
+      ))
+
+    mod.to_s.should_not contain("CONST")
+    mod.to_s.should_not contain("OTHER")
+  end
+
+  it "inlines bool const" do
+    mod = codegen(%(
+      CONST = true
+      CONST
+      ))
+
+    mod.to_s.should_not contain("CONST")
+  end
+
+  it "inlines char const" do
+    mod = codegen(%(
+      CONST = 'a'
+      CONST
+      ))
+
+    mod.to_s.should_not contain("CONST")
+  end
 end

src/compiler/crystal/codegen/codegen.cr

@@ -235,6 +235,8 @@ module Crystal
       @program.class_var_and_const_initializers.each do |initializer|
         case initializer
         when Const
+          # Simple constants are never initialized: they are always inlined
+          next if initializer.compile_time_value
           next unless initializer.simple?
 
           initialize_simple_const(initializer)
@@ -873,7 +875,7 @@ module Crystal
 
     def codegen_assign(target : Path, value, node)
       const = target.target_const.not_nil!
-      if const.used? && !const.simple?
+      if const.used? && !const.simple? && !const.compile_time_value
         initialize_const(const)
       end
       @last = llvm_nil

src/compiler/crystal/codegen/const.cr

@@ -154,12 +154,27 @@ class Crystal::CodeGenVisitor
   end
 
   def read_const(const)
-    @last = read_const_pointer(const)
-    @last = to_lhs @last, const.value.type
+    # We inline constants. Otherwise we use an LLVM const global.
+    @last =
+      case value = const.compile_time_value
+      when Bool   then int1(value ? 1 : 0)
+      when Char   then int32(value.ord)
+      when Int8   then int8(value)
+      when Int16  then int16(value)
+      when Int32  then int32(value)
+      when Int64  then int64(value)
+      when UInt8  then int8(value)
+      when UInt16 then int16(value)
+      when UInt32 then int32(value)
+      when UInt64 then int64(value)
+      else
+        last = read_const_pointer(const)
+        to_lhs last, const.value.type
+      end
   end
 
   def read_const_pointer(const)
-    if const == @program.argc || const == @program.argv
+    if const == @program.argc || const == @program.argv || const.initializer
       global_name = const.llvm_name
       global = declare_const(const)
 

src/compiler/crystal/codegen/types.cr

@@ -171,8 +171,36 @@ module Crystal
       "#{llvm_name}:init"
     end
 
+    # Returns `true` if this constant's value is a simple literal, like
+    # `nil`, a number, char, string or symbol literal.
     def simple?
       value.simple_literal?
     end
+
+    @compile_time_value : (Int16 | Int32 | Int64 | Int8 | UInt16 | UInt32 | UInt64 | UInt8 | Bool | Char | Nil)
+    @computed_compile_time_value = false
+
+    # Returns a value if this constant's value can be evaluated at
+    # compile time (things like `1 + 2` and such). Returns nil otherwise.
+    def compile_time_value
+      unless @computed_compile_time_value
+        @computed_compile_time_value = true
+
+        case value = self.value
+        when BoolLiteral
+          @compile_time_value = value.value
+        when CharLiteral
+          @compile_time_value = value.value
+        else
+          case type = value.type?
+          when IntegerType, EnumType
+            interpreter = MathInterpreter.new(namespace, visitor)
+            @compile_time_value = interpreter.interpret(value) rescue nil
+          end
+        end
+      end
+
+      @compile_time_value
+    end
   end
 end