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, 4 insertions, 2 deletions

diff --git a/src/sksl/ir/SkSLProgram.h b/src/sksl/ir/SkSLProgram.h
index ac49d6dcc7..6a73be6983 100644
--- a/src/sksl/ir/SkSLProgram.h
+++ b/src/sksl/ir/SkSLProgram.h
@@ -59,8 +59,8 @@ struct Program {
     , fSettings(settings)
     , fDefaultPrecision(defaultPrecision)
     , fContext(context)
-    , fElements(std::move(elements))
     , fSymbols(symbols)
+    , fElements(std::move(elements))
     , fInputs(inputs) {}
 
     Kind fKind;
@@ -68,8 +68,10 @@ struct Program {
     // FIXME handle different types; currently it assumes this is for floats
     Modifiers::Flag fDefaultPrecision;
     Context* fContext;
-    std::vector<std::unique_ptr<ProgramElement>> fElements;
+    // it's important to keep fElements defined after (and thus destroyed before) fSymbols,
+    // because destroying elements can modify reference counts in symbols
     std::shared_ptr<SymbolTable> fSymbols;
+    std::vector<std::unique_ptr<ProgramElement>> fElements;
     Inputs fInputs;
 };