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, 5 insertions, 14 deletions

diff --git a/src/sksl/SkSLCFGGenerator.h b/src/sksl/SkSLCFGGenerator.h
index 337fdfac35..c37850112c 100644
--- a/src/sksl/SkSLCFGGenerator.h
+++ b/src/sksl/SkSLCFGGenerator.h
@@ -27,23 +27,14 @@ struct BasicBlock {
         };
 
         Kind fKind;
-        // if false, this node should not be subject to constant propagation. This happens with
-        // compound assignment (i.e. x *= 2), in which the value x is used as an rvalue for
-        // multiplication by 2 and then as an lvalue for assignment purposes. Since there is only
-        // one "x" node, replacing it with a constant would break the assignment and we suppress
-        // it. Down the road, we should handle this more elegantly by substituting a regular
-        // assignment if the target is constant (i.e. x = 1; x *= 2; should become x = 1; x = 1 * 2;
-        // and then collapse down to a simple x = 2;).
-        bool fConstantPropagation;
-        std::unique_ptr<Expression>* fExpression;
-        const Statement* fStatement;
+        const IRNode* fNode;
     };
-
+    
     std::vector<Node> fNodes;
     std::set<BlockId> fEntrances;
     std::set<BlockId> fExits;
     // variable definitions upon entering this basic block (null expression = undefined)
-    DefinitionMap fBefore;
+    std::unordered_map<const Variable*, const Expression*> fBefore;
 };
 
 struct CFG {
@@ -86,9 +77,9 @@ public:
 private:
     void addStatement(CFG& cfg, const Statement* s);
 
-    void addExpression(CFG& cfg, std::unique_ptr<Expression>* e, bool constantPropagate);
+    void addExpression(CFG& cfg, const Expression* e);
 
-    void addLValue(CFG& cfg, std::unique_ptr<Expression>* e);
+    void addLValue(CFG& cfg, const Expression* e);
 
     std::stack<BlockId> fLoopContinues;
     std::stack<BlockId> fLoopExits;