Added constant propagation and better variable liveness tracking to skslc.

This allows skslc to track the values of variables with constant
values across multiple statements and replace variable references with
constant values where appropriate.

The improved liveness tracking allows skslc to realize that a
variable is no longer alive if all references to it have been
replaced. It is not yet doing much with this information; better
dead code elimination is coming in a followup change.

BUG=skia:

Change-Id: I068c5d2e9a362e75299b1de1f4575339f5ddc3bb
Reviewed-on: https://skia-review.googlesource.com/7302
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

1 files changed, 14 insertions, 4 deletions

diff --git a/src/sksl/ir/SkSLBinaryExpression.h b/src/sksl/ir/SkSLBinaryExpression.h
index 132513e7f7..de85e4812b 100644
--- a/src/sksl/ir/SkSLBinaryExpression.h
+++ b/src/sksl/ir/SkSLBinaryExpression.h
@@ -4,17 +4,19 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
- 
+
 #ifndef SKSL_BINARYEXPRESSION
 #define SKSL_BINARYEXPRESSION
 
 #include "SkSLExpression.h"
+#include "SkSLExpression.h"
+#include "../SkSLIRGenerator.h"
 #include "../SkSLToken.h"
 
 namespace SkSL {
 
 /**
- * A binary operation. 
+ * A binary operation.
  */
 struct BinaryExpression : public Expression {
     BinaryExpression(Position position, std::unique_ptr<Expression> left, Token::Kind op,
@@ -24,14 +26,22 @@ struct BinaryExpression : public Expression {
     , fOperator(op)
     , fRight(std::move(right)) {}
 
+    virtual std::unique_ptr<Expression> constantPropagate(
+                                                        const IRGenerator& irGenerator,
+                                                        const DefinitionMap& definitions) override {
+        return irGenerator.constantFold(*fLeft,
+                                        fOperator,
+                                        *fRight);
+    }
+
     virtual SkString description() const override {
         return "(" + fLeft->description() + " " + Token::OperatorName(fOperator) + " " +
                fRight->description() + ")";
     }
 
-    const std::unique_ptr<Expression> fLeft;
+    std::unique_ptr<Expression> fLeft;
     const Token::Kind fOperator;
-    const std::unique_ptr<Expression> fRight;
+    std::unique_ptr<Expression> fRight;
 
     typedef Expression INHERITED;
 };