cleaned up SkSL constant handling

Bug: skia:
Change-Id: I8131c4348f0f91bc2705e493918c4ca2d1f4867b
Reviewed-on: https://skia-review.googlesource.com/95920
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

src/sksl/SkSLIRGenerator.cpp

@@ -291,6 +291,7 @@ std::unique_ptr<VarDeclarations> IRGenerator::convertVarDeclarations(const ASTVa
             }
             value = this->coerce(std::move(value), *type);
             var->fWriteCount = 1;
+            var->fInitialValue = value.get();
         }
         if (storage == Variable::kGlobal_Storage && varDecl.fName == "sk_FragColor" &&
             (*fSymbolTable)[varDecl.fName]) {

src/sksl/ir/SkSLConstructor.h

@@ -146,15 +146,11 @@ struct Constructor : public Expression {
     }
 
     double getFVecComponent(int index) const {
-        const Expression& c = this->getVecComponent(index);
-        ASSERT(c.fKind == Expression::kFloatLiteral_Kind);
-        return ((FloatLiteral&) c).fValue;
+        return this->getVecComponent(index).getConstantFloat();
     }
 
     int64_t getIVecComponent(int index) const {
-        const Expression& c = this->getVecComponent(index);
-        ASSERT(c.fKind == Expression::kIntLiteral_Kind);
-        return ((IntLiteral&) c).fValue;
+        return this->getVecComponent(index).getConstantInt();
     }
 
     // null return should be interpreted as zero

src/sksl/ir/SkSLExpression.h

@@ -66,6 +66,22 @@ struct Expression : public IRNode {
         ABORT("cannot call compareConstant on this type");
     }
 
+    /**
+     * For an expression which evaluates to a constant int, returns the value. Otherwise calls
+     * ABORT.
+     */
+    virtual int64_t getConstantInt() const {
+        ABORT("not a constant int");
+    }
+
+    /**
+     * For an expression which evaluates to a constant float, returns the value. Otherwise calls
+     * ABORT.
+     */
+    virtual double getConstantFloat() const {
+        ABORT("not a constant float");
+    }
+
     /**
      * Returns true if evaluating the expression potentially has side effects. Expressions may never
      * return false if they actually have side effects, but it is legal (though suboptimal) to

src/sksl/ir/SkSLFloatLiteral.h

@@ -39,6 +39,10 @@ struct FloatLiteral : public Expression {
         return fValue == f.fValue;
     }
 
+    double getConstantFloat() const override {
+        return fValue;
+    }
+
     const double fValue;
 
     typedef Expression INHERITED;

src/sksl/ir/SkSLIntLiteral.h

@@ -47,6 +47,10 @@ struct IntLiteral : public Expression {
         return INHERITED::coercionCost(target);
     }
 
+    int64_t getConstantInt() const override {
+        return fValue;
+    }
+
     const int64_t fValue;
 
     typedef Expression INHERITED;