Optimize one byte string comparisons.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 31282)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -669,7 +669,7 @@
   M(UnaryMintOp)                                                               \
   M(CheckArrayBound)                                                           \
   M(Constraint)                                                                \
-  M(StringFromCharCode)                                                        \
+  M(StringCharCode)                                                            \
   M(StringInterpolate)                                                         \
   M(InvokeMathCFunction)                                                       \
   M(MergedMath)                                                                \
@@ -3664,20 +3664,41 @@
 };
 
 
-class StringFromCharCodeInstr : public TemplateDefinition<1> {
+// Either converts a char-code to a string or a string to a charcode (-1 if
+// string is not of length one).
+class StringCharCodeInstr : public TemplateDefinition<1> {

[Florian Schneider, 2013/12/20 09:29:12]

Why packing two different instructions into one? I'd rather have ToCharCode and
FromCharCode as separate instructions. They don't seem to share much code
anyway.

[srdjan, 2013/12/20 19:48:03]

Split it up in two instructions.

  public:
-  StringFromCharCodeInstr(Value* char_code, intptr_t cid) : cid_(cid) {
-    ASSERT(char_code != NULL);
-    ASSERT(char_code->definition()->IsLoadIndexed() &&
-           (char_code->definition()->AsLoadIndexed()->class_id() ==
-            kOneByteStringCid));
-    SetInputAt(0, char_code);
+  enum Kind {
+    kFromCharCode,
+    kToCharCode,
+  };
+  StringCharCodeInstr(Value* val,
+                      intptr_t cid,
+                      StringCharCodeInstr::Kind kind)
+      : cid_(cid), kind_(kind) {
+    ASSERT(val != NULL);
+    if (kind == kFromCharCode) {
+      ASSERT(val->definition()->IsLoadIndexed() &&
+             (val->definition()->AsLoadIndexed()->class_id() ==
+              kOneByteStringCid));
+    } else {
+      ASSERT(kind == kToCharCode);
+    }
+    SetInputAt(0, val);
   }
 
-  DECLARE_INSTRUCTION(StringFromCharCode)
+  DECLARE_INSTRUCTION(StringCharCode)
   virtual CompileType ComputeType() const;
 
-  Value* char_code() const { return inputs_[0]; }
+  Value* char_code() const {
+    ASSERT(kind_ == kFromCharCode);
+    return inputs_[0];
+  }
+  Value* str() const {
+    ASSERT(kind_ == kToCharCode);
+    return inputs_[0];
+  }
+  StringCharCodeInstr::Kind kind() const { return kind_; }
 
   virtual bool CanDeoptimize() const { return false; }
 
@@ -3685,15 +3706,19 @@
   virtual EffectSet Effects() const { return EffectSet::None(); }
   virtual EffectSet Dependencies() const { return EffectSet::None(); }
   virtual bool AttributesEqual(Instruction* other) const {
-    return other->AsStringFromCharCode()->cid_ == cid_;
+    return (other->AsStringCharCode()->cid_ == cid_) &&
+        (other->AsStringCharCode()->kind_ == kind_);
   }
 
   virtual bool MayThrow() const { return false; }
 
+  virtual void PrintTo(BufferFormatter* f) const;
+
  private:
   const intptr_t cid_;
+  const Kind kind_;
 
-  DISALLOW_COPY_AND_ASSIGN(StringFromCharCodeInstr);
+  DISALLOW_COPY_AND_ASSIGN(StringCharCodeInstr);
 };