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, 2 insertions, 69 deletions

diff --git a/src/sksl/ir/SkSLVariableReference.h b/src/sksl/ir/SkSLVariableReference.h
index fecb04e2e5..c6a2ea0511 100644
--- a/src/sksl/ir/SkSLVariableReference.h
+++ b/src/sksl/ir/SkSLVariableReference.h
@@ -20,83 +20,16 @@ namespace SkSL {
  * there is only one Variable 'x', but two VariableReferences to it.
  */
 struct VariableReference : public Expression {
-    enum RefKind {
-        kRead_RefKind,
-        kWrite_RefKind,
-        kReadWrite_RefKind
-    };
-
-    VariableReference(Position position, const Variable& variable, RefKind refKind = kRead_RefKind)
+    VariableReference(Position position, const Variable& variable)
     : INHERITED(position, kVariableReference_Kind, variable.fType)
-    , fVariable(variable)
-    , fRefKind(refKind) {
-        if (refKind != kRead_RefKind) {
-            fVariable.fWriteCount++;
-        }
-        if (refKind != kWrite_RefKind) {
-            fVariable.fReadCount++;
-        }
-    }
-
-    virtual ~VariableReference() override {
-        if (fRefKind != kWrite_RefKind) {
-            fVariable.fReadCount--;
-        }
-    }
-
-    RefKind refKind() {
-        return fRefKind;
-    }
-
-    void setRefKind(RefKind refKind) {
-        if (fRefKind != kRead_RefKind) {
-            fVariable.fWriteCount--;
-        }
-        if (fRefKind != kWrite_RefKind) {
-            fVariable.fReadCount--;
-        }
-        if (refKind != kRead_RefKind) {
-            fVariable.fWriteCount++;
-        }
-        if (refKind != kWrite_RefKind) {
-            fVariable.fReadCount++;
-        }
-        fRefKind = refKind;
-    }
+    , fVariable(variable) {}
 
     SkString description() const override {
         return fVariable.fName;
     }
 
-    virtual std::unique_ptr<Expression> constantPropagate(
-                                                        const IRGenerator& irGenerator,
-                                                        const DefinitionMap& definitions) override {
-        auto exprIter = definitions.find(&fVariable);
-        if (exprIter != definitions.end() && exprIter->second) {
-            const Expression* expr = exprIter->second->get();
-            switch (expr->fKind) {
-                case Expression::kIntLiteral_Kind:
-                    return std::unique_ptr<Expression>(new IntLiteral(
-                                                                     irGenerator.fContext,
-                                                                     Position(),
-                                                                     ((IntLiteral*) expr)->fValue));
-                case Expression::kFloatLiteral_Kind:
-                    return std::unique_ptr<Expression>(new FloatLiteral(
-                                                                   irGenerator.fContext,
-                                                                   Position(),
-                                                                   ((FloatLiteral*) expr)->fValue));
-                default:
-                    break;
-            }
-        }
-        return nullptr;
-    }
-
     const Variable& fVariable;
 
-private:
-    RefKind fRefKind;
-
     typedef Expression INHERITED;
 };