llvm dev - May 2008 - [LLVMdev] Some positive feedback :)

I continue to be pleasantly surprised at how well LLVM works. Working 
with it is certainly a treat.

As an example, tonight I implemented structure types (i.e. aggregate 
types that are passed as values, not references) in my front end, and I 
wrote up this little unit test:

    struct Vector {
      var x:int;
      var y:int;
      var z:int;
     
      def Vector(x:int, y:int, z:int) {
        self.x = x;
        self.y = y;
        self.z = z;
      }

      def Vector() {
        self.x = 0;
        self.y = 0;
        self.z = 0;
      }
    }

    [EntryPoint]
    def main(args:String[]) {
      var v0:Vector = Vector();
      assert(v0.x == 0);
      assert(v0.y == 0);
      assert(v0.z == 0);

      let v1 = Vector(2, 3, 4);
      assert(v1.x == 2);
      assert(v1.y == 3);
      assert(v1.z == 4);

      v0 = v1;
      assert(v0.x == 2);
      assert(v0.y == 3);
      assert(v0.z == 4);
    }

After making a few tweaks to my code generator, it passed all of the 
tests...which was surprising enough. But then I turned on optimization 
-- and lo and behold, it converted every one of those asserts to 
"assert(1)", and completely eliminated everything else! If it had been
able to inline the asserts (which I am still working on), it would have 
eliminated the body of main entirely.

Now that's the kind of optimization I like to see :)

-- Talin

On Apr 30, 2008, at 9:42 PM, Talin wrote:
> I continue to be pleasantly surprised at how well LLVM works. Working
> with it is certainly a treat.
> After making a few tweaks to my code generator, it passed all of the
> tests...which was surprising enough. But then I turned on optimization
> -- and lo and behold, it converted every one of those asserts to  
> "assert(1)", and completely eliminated everything else! If it had
been
> able to inline the asserts (which I am still working on), it would  
> have
> eliminated the body of main entirely.
>
> Now that's the kind of optimization I like to see :)
Awesome!

-Chris

Chris Lattner wrote:
> On Apr 30, 2008, at 9:42 PM, Talin wrote:
>   
>> I continue to be pleasantly surprised at how well LLVM works. Working
>> with it is certainly a treat.
>>     
>
>   
>> After making a few tweaks to my code generator, it passed all of the
>> tests...which was surprising enough. But then I turned on optimization
>> -- and lo and behold, it converted every one of those asserts to  
>> "assert(1)", and completely eliminated everything else! If it
had been
>> able to inline the asserts (which I am still working on), it would  
>> have
>> eliminated the body of main entirely.
>>
>> Now that's the kind of optimization I like to see :)
>>     
>
> Awesome!
>   
Here's another code sample that boils down to "assert(true)" when 
optimization is turned on:

    struct CountIterator(Iterator<int>) {
      private var count:int;
      def CountIterator(count:int) { self.count = count; }
      def atEnd:bool { get { return count <= 0; } }
      def current:int { get { return count; } }
      def next() { --count; }
    }

    def testSimpleIterator() {
      var sum = 0;
      for i in CountIterator(5) {
        sum = sum + i;
      }
     
      assert(sum == 15);
    }

-- Talin