cmd/compile: finish GOEXPERIMENT=preemptibleloops repair

A newish check for branch-likely on single-successor blocks caught a case where the preemption-check inserter was setting "likely" on an unconditional branch. Fixed by checking for that case before setting likely. Also removed an overconservative restriction on parallel compilation for GOEXPERIMENT=preemptibleloops; it works fine, it is just another control-flow transformation. Change-Id: I8e786e6281e0631cac8d80cff67bfb6402b4d225 Reviewed-on: https://go-review.googlesource.com/102317 Run-TryBot: David Chase <drchase@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Austin Clements <austin@google.com>
golang · Mar 26, 2018 · f740497 · f740497
1 parent 8afa8a3
commit f740497
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diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
@@ -1223,7 +1223,7 @@ func concurrentBackendAllowed() bool {
 		return false
 	}
 	// TODO: Test and delete these conditions.
-	if objabi.Fieldtrack_enabled != 0 || objabi.Preemptibleloops_enabled != 0 || objabi.Clobberdead_enabled != 0 {
+	if objabi.Fieldtrack_enabled != 0 || objabi.Clobberdead_enabled != 0 {
 		return false
 	}
 	// TODO: fix races and enable the following flags

diff --git a/src/cmd/compile/internal/ssa/loopreschedchecks.go b/src/cmd/compile/internal/ssa/loopreschedchecks.go
@@ -179,7 +179,9 @@ func insertLoopReschedChecks(f *Func) {
 		if p.i != 0 {
 			likely = BranchUnlikely
 		}
-		bb.Likely = likely
+		if bb.Kind != BlockPlain { // backedges can be unconditional. e.g., if x { something; continue }
+			bb.Likely = likely
+		}
 
 		// rewrite edge to include reschedule check
 		// existing edges: