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, 3 insertions, 4 deletions

diff --git a/src/sksl/SkSLCompiler.h b/src/sksl/SkSLCompiler.h
index 0f893f7e64..fdca12d2cf 100644
--- a/src/sksl/SkSLCompiler.h
+++ b/src/sksl/SkSLCompiler.h
@@ -60,11 +60,10 @@ public:
     }
 
 private:
-    void addDefinition(const Expression* lvalue, const Expression* expr,
-                       std::unordered_map<const Variable*, const Expression*>* definitions);
+    void addDefinition(const Expression* lvalue, std::unique_ptr<Expression>* expr,
+                       DefinitionMap* definitions);
 
-    void addDefinitions(const BasicBlock::Node& node,
-                        std::unordered_map<const Variable*, const Expression*>* definitions);
+    void addDefinitions(const BasicBlock::Node& node, DefinitionMap* definitions);
 
     void scanCFG(CFG* cfg, BlockId block, std::set<BlockId>* workList);