diff options
Diffstat (limited to 'src/cmd/compile/internal/ssa/writebarrier.go')
| -rw-r--r-- | src/cmd/compile/internal/ssa/writebarrier.go | 35 |
1 files changed, 9 insertions, 26 deletions
diff --git a/src/cmd/compile/internal/ssa/writebarrier.go b/src/cmd/compile/internal/ssa/writebarrier.go index 02f5649d59..d2e10cab62 100644 --- a/src/cmd/compile/internal/ssa/writebarrier.go +++ b/src/cmd/compile/internal/ssa/writebarrier.go @@ -197,8 +197,6 @@ func writebarrier(f *Func) { // order values in store order b.Values = storeOrder(b.Values, sset, storeNumber) - - firstSplit := true again: // find the start and end of the last contiguous WB store sequence. // a branch will be inserted there. values after it will be moved @@ -374,17 +372,19 @@ func writebarrier(f *Func) { } // merge memory - // Splice memory Phi into the last memory of the original sequence, - // which may be used in subsequent blocks. Other memories in the - // sequence must be dead after this block since there can be only - // one memory live. + mem = bEnd.NewValue2(pos, OpPhi, types.TypeMem, memThen, memElse) + // The last store becomes the WBend marker. This marker is used by the liveness + // pass to determine what parts of the code are preemption-unsafe. + // All subsequent memory operations use this memory, so we have to sacrifice the + // previous last memory op to become this new value. bEnd.Values = append(bEnd.Values, last) last.Block = bEnd - last.reset(OpPhi) + last.reset(OpWBend) last.Pos = last.Pos.WithNotStmt() last.Type = types.TypeMem - last.AddArg(memThen) - last.AddArg(memElse) + last.AddArg(mem) + + // Free all the old stores, except last which became the WBend marker. for _, w := range stores { if w != last { w.resetArgs() @@ -402,23 +402,6 @@ func writebarrier(f *Func) { w.Block = bEnd } - // Preemption is unsafe between loading the write - // barrier-enabled flag and performing the write - // because that would allow a GC phase transition, - // which would invalidate the flag. Remember the - // conditional block so liveness analysis can disable - // safe-points. This is somewhat subtle because we're - // splitting b bottom-up. - if firstSplit { - // Add b itself. - b.Func.WBLoads = append(b.Func.WBLoads, b) - firstSplit = false - } else { - // We've already split b, so we just pushed a - // write barrier test into bEnd. - b.Func.WBLoads = append(b.Func.WBLoads, bEnd) - } - // if we have more stores in this block, do this block again if nWBops > 0 { goto again |