diff options
Diffstat (limited to 'src/compiler/scala/tools/nsc/backend/opt/ConstantOptimization.scala')
| -rw-r--r-- | src/compiler/scala/tools/nsc/backend/opt/ConstantOptimization.scala | 51 |
1 files changed, 25 insertions, 26 deletions
diff --git a/src/compiler/scala/tools/nsc/backend/opt/ConstantOptimization.scala b/src/compiler/scala/tools/nsc/backend/opt/ConstantOptimization.scala index ff93206ffd..8a85873e94 100644 --- a/src/compiler/scala/tools/nsc/backend/opt/ConstantOptimization.scala +++ b/src/compiler/scala/tools/nsc/backend/opt/ConstantOptimization.scala @@ -17,7 +17,7 @@ import scala.annotation.tailrec * null checks. * * With some more work it could be extended to - * - cache stable values (final fields, modules) in locals + * - cache stable values (final fields, modules) in locals * - replace the copy propagation in ClosureElilmination * - fold constants * - eliminate unnecessary stores and loads @@ -118,18 +118,18 @@ abstract class ConstantOptimization extends SubComponent { * * // left must be 1 or 2, right must be 2 or 3 then we must have a 1, 2 or 3 * Possible(xs) merge Possible(ys) => Possible(xs union ys) - * + * * // Left says can't be 2 or 3, right says can't be 3 or 4 * // then it's not 3 (it could be 2 from the right or 4 from the left) * Impossible(xs) merge Impossible(ys) => Impossible(xs intersect ys) - * + * * // Left says it can't be 2 or 3, right says it must be 3 or 4, then * // it can't be 2 (left rules out 4 and right says 3 is possible) * Impossible(xs) merge Possible(ys) => Impossible(xs -- ys) - * + * * Intuitively, Possible(empty) says that a location can't hold anything, * it's uninitialized. However, Possible(empty) never appears in the code. - * + * * Conversely, Impossible(empty) says nothing is impossible, it could be * anything. Impossible(empty) is given a synonym UNKNOWN and is used * for, e.g., the result of an arbitrary method call. @@ -155,7 +155,7 @@ abstract class ConstantOptimization extends SubComponent { def mightNotEqual(other: Contents): Boolean } private def SingleImpossible(x: Datum) = new Impossible(Set(x)) - + /** * The location is known to have one of a set of values. */ @@ -299,32 +299,32 @@ abstract class ConstantOptimization extends SubComponent { private def interpretInst(in: State, inst: Instruction): State = { // pop the consumed number of values off the `in` state's stack, producing a new state def dropConsumed: State = in drop inst.consumed - + inst match { case THIS(_) => in load THIS_LOCAL - + case CONSTANT(k) => // treat NaN as UNKNOWN because NaN must never equal NaN val const = if (k.isNaN) UNKNOWN else SinglePossible(Const(k)) in push const - + case LOAD_ARRAY_ITEM(_) | LOAD_FIELD(_, _) | CALL_PRIMITIVE(_) => dropConsumed push UNKNOWN case LOAD_LOCAL(local) => // TODO if a local is known to hold a constant then we can replace this instruction with a push of that constant in load local - + case STORE_LOCAL(local) => in store local - + case STORE_THIS(_) => // if a local is already known to have a constant and we're replacing with the same constant then we can // replace this with a drop in store THIS_LOCAL - + case CALL_METHOD(_, _) => // TODO we could special case implementations of equals that are known, e.g. String#equals // We could turn Possible(string constants).equals(Possible(string constants) into an eq check @@ -332,7 +332,7 @@ abstract class ConstantOptimization extends SubComponent { // and eliminate the null check that likely precedes this call val initial = dropConsumed (0 until inst.produced).foldLeft(initial) { case (know, _) => know push UNKNOWN } - + case BOX(_) => val value = in peek 0 // we simulate boxing by, um, boxing the possible/impossible contents @@ -345,7 +345,7 @@ abstract class ConstantOptimization extends SubComponent { case Impossible(values) => Impossible(values map Boxed) } dropConsumed push newValue - + case UNBOX(_) => val value = in peek 0 val newValue = value match { @@ -373,42 +373,42 @@ abstract class ConstantOptimization extends SubComponent { } } dropConsumed push newValue - + case LOAD_MODULE(_) | NEW(_) | LOAD_EXCEPTION(_) => in push NOT_NULL case CREATE_ARRAY(_, _) => dropConsumed push NOT_NULL - + case IS_INSTANCE(_) => // TODO IS_INSTANCE is going to be followed by a C(Z)JUMP // and if IS_INSTANCE/C(Z)JUMP the branch for "true" can // know that whatever was checked was not a null // see the TODO on CJUMP for more information about propagating null // information - // TODO if the top of stack is guaranteed null then we can eliminate this IS_INSTANCE check and + // TODO if the top of stack is guaranteed null then we can eliminate this IS_INSTANCE check and // replace with a constant false, but how often is a knowable null checked for instanceof? // TODO we could track type information and statically know to eliminate IS_INSTANCE // which might be a nice win under specialization dropConsumed push UNKNOWN // it's actually a Possible(true, false) but since the following instruction // will be a conditional jump comparing to true or false there // nothing to be gained by being more precise - + case CHECK_CAST(_) => // TODO we could track type information and statically know to eliminate CHECK_CAST // but that's probably not a huge win in - + case DUP(_) => val value = in peek 0 in push value - + case DROP(_) | MONITOR_ENTER() | MONITOR_EXIT() | STORE_ARRAY_ITEM(_) | STORE_FIELD(_, _) => dropConsumed case SCOPE_ENTER(_) | SCOPE_EXIT(_) => in - + case JUMP(_) | CJUMP(_, _, _, _) | CZJUMP(_, _, _, _) | RETURN(_) | THROW(_) | SWITCH(_, _) => dumpClassesAndAbort("Unexpected block ending instruction: " + inst) } @@ -468,7 +468,7 @@ abstract class ConstantOptimization extends SubComponent { val replacements = if (result.size == 1) List.fill(inst.consumed)(DROP(kind)) :+ JUMP(result.keySet.head) else inst :: Nil - + (result, replacements) } @@ -488,8 +488,7 @@ abstract class ConstantOptimization extends SubComponent { case SWITCH(tags, labels) => val in1 = in peek 0 - val newStuff = tags zip labels filter { case (tagSet, _) => canSwitch(in1, tagSet) } - val (reachableTags, reachableNormalLabels) = (tags zip labels filter { case (tagSet, _) => canSwitch(in1, tagSet) }).unzip + val reachableNormalLabels = tags zip labels collect { case (tagSet, label) if canSwitch(in1, tagSet) => label } val reachableLabels = if (labels.lengthCompare(tags.length) > 0) { // if we've got an extra label then it's the default val defaultLabel = labels.last @@ -533,7 +532,7 @@ abstract class ConstantOptimization extends SubComponent { // number of instructions excluding the last one val normalCount = block.size - 1 - var exceptionState = in.cleanStack + val exceptionState = in.cleanStack var normalExitState = in var idx = 0 while (idx < normalCount) { @@ -569,7 +568,7 @@ abstract class ConstantOptimization extends SubComponent { // worklist of basic blocks to process, initially the start block val worklist = MSet(m.startBlock) - // worklist of exception basic blocks. They're kept in a separate set so they can be + // worklist of exception basic blocks. They're kept in a separate set so they can be // processed after normal flow basic blocks. That's because exception basic blocks // are more likely to have multiple predecessors and queueing them for later // increases the chances that they'll only need to be interpreted once |