simplification to HClampToUint8

* src/hydrogen-instructions.h (HClampToUint8): Don't mark as having
  flexible representation; instead the output is always an Integer32.
  There is no input representation restriction, so we can still perform
  input-specific truncation.

I tested by looking at the --print-code of

var a = PixelArray(1000000)
function fill(a,x) { for (var i=0; i<a.len; i++) a[i] = x; }

Seems to optimize fine both for double and integer inputs.  But perhaps
there is a better test, for which the original code does better, and
this is a bogus patch.

Review URL: http://codereview.chromium.org/7357003
Patch from Andy Wingo <wingo@igalia.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8650 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 46d5393..93a7073 100644 (file)
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -1123,40 +1123,19 @@ class HChange: public HUnaryOperation {
 class HClampToUint8: public HUnaryOperation {
  public:
   explicit HClampToUint8(HValue* value)
-      : HUnaryOperation(value),
-        input_rep_(Representation::None()) {
-    SetFlag(kFlexibleRepresentation);
-    set_representation(Representation::Tagged());
+      : HUnaryOperation(value) {
+    set_representation(Representation::Integer32());
     SetFlag(kUseGVN);
   }
 
   virtual Representation RequiredInputRepresentation(int index) const {
-    return input_rep_;
-  }
-
-  virtual Representation InferredRepresentation() {
-    // TODO(danno): Inference on input types should happen separately from
-    // return representation.
-    Representation new_rep = value()->representation();
-    if (input_rep_.IsNone()) {
-      if (!new_rep.IsNone()) {
-        input_rep_ = new_rep;
-        return Representation::Integer32();
-      } else {
-        return Representation::None();
-      }
-    } else {
-      return Representation::Integer32();
-    }
+    return Representation::None();
   }
 
   DECLARE_CONCRETE_INSTRUCTION(ClampToUint8)
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
-
- private:
-  Representation input_rep_;
 };