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Allow forcing traces #5738

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Merged
merged 2 commits into from
Mar 26, 2019
Merged

Allow forcing traces #5738

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83e6ad4
Allow forcing traces
abgruszecki Jan 14, 2019
9fb3521
Document `trace`/`trace.force`
abgruszecki Mar 12, 2019
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47 changes: 35 additions & 12 deletions compiler/src/dotty/tools/dotc/reporting/trace.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -7,34 +7,50 @@ import config.Config
import config.Printers
import core.Mode

object trace {
/** Exposes the {{{ trace("question") { op } }}} syntax.
*
* Traced operations will print indented messages if enabled.
* Tracing depends on [[Config.tracingEnabled]] and [[dotty.tools.dotc.config.ScalaSettings.Ylog]].
* Tracing can be forced by replacing [[trace]] with [[trace.force]] (see below).
*/
object trace extends TraceSyntax {
final val isForced = false

/** Forces a particular trace to be printed out regardless of tracing being enabled. */
object force extends TraceSyntax {
final val isForced = true
}
}

abstract class TraceSyntax {
val isForced: Boolean
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Use a field TraceSyntax(isForced: Boolean)? I would expect it is cheaper

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Could you be more clear on what it is you call a field? The goal here is to override isForced with a final val, which should be guaranteed to be inlined whenever referenced, which would then mean that we get rid of useless branches in the inlined logging methods. This is somewhat moot, since forceInline does not seem to inline nested methods properly ( see #5738 (comment) ), but I don't see how making isForced a constructor argument makes it any cheaper.

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Here the final val implements an abstract one. It will be compiled to a virtual method call, I don't think the compiler can inline in this case. If isForced is a constructor argument, it will be compiled to a field. A field access is much cheaper than a virtual method call.

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I see the reasoning, but all the methods that access isForced are @forceInline, so after the body is inlined the compiler should see that the member being accessed is a final val and therefore is inlineable, no? Anyway, this PR has no impact on performance and after we bootstrap we will probably rewrite all the methods in this class to inline, which will guarantee that they are inlined the way we want.

Side note: I am bookmarking this discussion to show the next person that tries to convince me it's a good idea to rely on the optimizer for inlining.


@forceInline
def onDebug[TD](question: => String)(op: => TD)(implicit ctx: Context): TD =
conditionally(ctx.settings.YdebugTrace.value, question, false)(op)

@forceInline
def conditionally[TC](cond: Boolean, question: => String, show: Boolean)(op: => TC)(implicit ctx: Context): TC =
if (Config.tracingEnabled) {
if (isForced || Config.tracingEnabled) {
def op1 = op
if (cond) apply[TC](question, Printers.default, show)(op1)
else op1
} else op

@forceInline
def apply[T](question: => String, printer: Printers.Printer, showOp: Any => String)(op: => T)(implicit ctx: Context): T =
if (Config.tracingEnabled) {
if (isForced || Config.tracingEnabled) {
def op1 = op
if (printer.eq(config.Printers.noPrinter)) op1
if (!isForced && printer.eq(config.Printers.noPrinter)) op1
else doTrace[T](question, printer, showOp)(op1)
}
else op

@forceInline
def apply[T](question: => String, printer: Printers.Printer, show: Boolean)(op: => T)(implicit ctx: Context): T =
if (Config.tracingEnabled) {
if (isForced || Config.tracingEnabled) {
def op1 = op
if (printer.eq(config.Printers.noPrinter)) op1
if (!isForced && printer.eq(config.Printers.noPrinter)) op1
else doTrace[T](question, printer, if (show) showShowable(_) else alwaysToString)(op1)
}
else op
Expand Down Expand Up @@ -68,20 +84,27 @@ object trace {
apply[T](s"==> $q?", (res: Any) => s"<== $q = ${showOp(res)}")(op)
}

def apply[T](leading: => String, trailing: Any => String)(op: => T)(implicit ctx: Context): T =
def apply[T](leading: => String, trailing: Any => String)(op: => T)(implicit ctx: Context): T = {
val log: String => Unit = if (isForced) Console.println else {
var logctx = ctx
while (logctx.reporter.isInstanceOf[StoreReporter]) logctx = logctx.outer
logctx.log(_)
}
doApply(leading, trailing, log)(op)
}

def doApply[T](leading: => String, trailing: Any => String, log: String => Unit)(op: => T)(implicit ctx: Context): T =
if (ctx.mode.is(Mode.Printing)) op
else {
var finalized = false
var logctx = ctx
while (logctx.reporter.isInstanceOf[StoreReporter]) logctx = logctx.outer
def finalize(result: Any, note: String) =
if (!finalized) {
ctx.base.indent -= 1
logctx.log(s"${ctx.base.indentTab * ctx.base.indent}${trailing(result)}$note")
log(s"${ctx.base.indentTab * ctx.base.indent}${trailing(result)}$note")
finalized = true
}
try {
logctx.log(s"${ctx.base.indentTab * ctx.base.indent}$leading")
log(s"${ctx.base.indentTab * ctx.base.indent}$leading")
ctx.base.indent += 1
val res = op
finalize(res, "")
Expand All @@ -92,4 +115,4 @@ object trace {
throw ex
}
}
}
}