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cmd/compile: only clobber dead slots at call sites 

We now have safepoints at nearly all the instructions. When
GOEXPERIMENT=clobberdead is on, it inserts clobbers nearly at
every instruction. Currently this doesn't work. (Maybe the stack
maps at non-call safepoints are still imprecise. I haven't
investigated.) For now, only use call-based safepoints if the
experiment is on.

Updates #27326.

Change-Id: I72cda9b422d9637cc5738e681502035af7a5c02d
Reviewed-on: https://go-review.googlesource.com/131956
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Cherry Zhang 2018-08-29 11:55:55 -04:00
parent c99687f87a
commit c8545722a1
1 changed files with 2 additions and 2 deletions
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4
src/cmd/compile/internal/gc/plive.go
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@ -671,7 +671,7 @@ func (lv *Liveness) pointerMap(liveout bvec, vars []*Node, args, locals bvec) {
// markUnsafePoints finds unsafe points and computes lv.unsafePoints. // markUnsafePoints finds unsafe points and computes lv.unsafePoints.
func (lv *Liveness) markUnsafePoints() { func (lv *Liveness) markUnsafePoints() {
if compiling_runtime || lv.f.NoSplit { if compiling_runtime || lv.f.NoSplit || objabi.Clobberdead_enabled != 0 {
// No complex analysis necessary. Do this on the fly // No complex analysis necessary. Do this on the fly
// in issafepoint. // in issafepoint.
return return
@ -830,7 +830,7 @@ func (lv *Liveness) issafepoint(v *ssa.Value) bool {
// go:nosplit functions are similar. Since safe points used to // go:nosplit functions are similar. Since safe points used to
// be coupled with stack checks, go:nosplit often actually // be coupled with stack checks, go:nosplit often actually
// means "no safe points in this function". // means "no safe points in this function".
if compiling_runtime || lv.f.NoSplit { if compiling_runtime || lv.f.NoSplit || objabi.Clobberdead_enabled != 0 {
return v.Op.IsCall() return v.Op.IsCall()
} }
switch v.Op { switch v.Op {