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: I6bf267d478b769caf0063ac3597dc16bbe618cb4
Reviewed-on: https://skia-review.googlesource.com/7033
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/sksl/ir/SkSLForStatement.h b/src/sksl/ir/SkSLForStatement.h
index ff03d0d7f9..6f03e2bb36 100644
--- a/src/sksl/ir/SkSLForStatement.h
+++ b/src/sksl/ir/SkSLForStatement.h
@@ -46,8 +46,8 @@ struct ForStatement : public Statement {
     }
 
     const std::unique_ptr<Statement> fInitializer;
-    const std::unique_ptr<Expression> fTest;
-    const std::unique_ptr<Expression> fNext;
+    std::unique_ptr<Expression> fTest;
+    std::unique_ptr<Expression> fNext;
     const std::unique_ptr<Statement> fStatement;
     const std::shared_ptr<SymbolTable> fSymbols;