Revert "Added constant propagation and better variable liveness tracking to"

This reverts commit f54b07121f81a56145fb118a2e18841fc135717d.

Reason for revert: ASAN failure

Original change's description:
> 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>
> 

TBR=egdaniel@google.com,ethannicholas@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Change-Id: Id2e26bce96b27df73948f8b32d3dff2e358ae0d6
Reviewed-on: https://skia-review.googlesource.com/7274
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>

1 files changed, 3 insertions, 22 deletions

diff --git a/src/sksl/ir/SkSLExpression.h b/src/sksl/ir/SkSLExpression.h
index f87d810fc0..b4ed37c09a 100644
--- a/src/sksl/ir/SkSLExpression.h
+++ b/src/sksl/ir/SkSLExpression.h
@@ -4,24 +4,17 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
-
+ 
 #ifndef SKSL_EXPRESSION
 #define SKSL_EXPRESSION
 
+#include "SkSLIRNode.h"
 #include "SkSLType.h"
-#include "SkSLVariable.h"
-
-#include <unordered_map>
 
 namespace SkSL {
 
-struct Expression;
-class IRGenerator;
-
-typedef std::unordered_map<const Variable*, std::unique_ptr<Expression>*> DefinitionMap;
-
 /**
- * Abstract supertype of all expressions.
+ * Abstract supertype of all expressions. 
  */
 struct Expression : public IRNode {
     enum Kind {
@@ -52,18 +45,6 @@ struct Expression : public IRNode {
         return false;
     }
 
-    /**
-     * Given a map of known constant variable values, substitute them in for references to those
-     * variables occurring in this expression and its subexpressions.  Similar simplifications, such
-     * as folding a constant binary expression down to a single value, may also be performed.
-     * Returns a new expression which replaces this expression, or null if no replacements were
-     * made. If a new expression is returned, this expression is no longer valid.
-     */
-    virtual std::unique_ptr<Expression> constantPropagate(const IRGenerator& irGenerator,
-                                                          const DefinitionMap& definitions) {
-        return nullptr;
-    }
-
     const Kind fKind;
     const Type& fType;