Minor: RedundantCoercionToUnit -> PopBackwardPropagation

It is actually more meaningful than just "coercion to unit elision":
it removes instructions without side effects with results that are
unused (popped from the stack).

compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/OptimizationMethodVisitor.kt

@@ -18,7 +18,7 @@ package org.jetbrains.kotlin.codegen.optimization
 
 import org.jetbrains.kotlin.codegen.TransformationMethodVisitor
 import org.jetbrains.kotlin.codegen.optimization.boxing.RedundantBoxingMethodTransformer
-import org.jetbrains.kotlin.codegen.optimization.boxing.RedundantCoercionToUnitTransformer
+import org.jetbrains.kotlin.codegen.optimization.boxing.PopBackwardPropagationTransformer
 import org.jetbrains.kotlin.codegen.optimization.common.prepareForEmitting
 import org.jetbrains.kotlin.codegen.optimization.nullCheck.RedundantNullCheckMethodTransformer
 import org.jetbrains.kotlin.codegen.optimization.transformer.CompositeMethodTransformer
@@ -54,7 +54,7 @@ class OptimizationMethodVisitor(
                 RedundantCheckCastEliminationMethodTransformer(),
                 ConstantConditionEliminationMethodTransformer(),
                 RedundantBoxingMethodTransformer(),
-                RedundantCoercionToUnitTransformer(),
+                PopBackwardPropagationTransformer(),
                 DeadCodeEliminationMethodTransformer(),
                 RedundantGotoMethodTransformer(),
                 RedundantNopsCleanupMethodTransformer()

compiler/backend/src/org/jetbrains/kotlin/codegen/optimization/boxing/PopBackwardPropagationTransformer.kt

@@ -30,7 +30,7 @@ import org.jetbrains.org.objectweb.asm.tree.analysis.SourceInterpreter
 import org.jetbrains.org.objectweb.asm.tree.analysis.SourceValue
 import java.util.*
 
-class RedundantCoercionToUnitTransformer : MethodTransformer() {
+class PopBackwardPropagationTransformer : MethodTransformer() {
     override fun transform(internalClassName: String, methodNode: MethodNode) {
         Transformer(methodNode).transform()
     }