From 85b2940f5c82e00ccc7f60ba2816cea0d418a950 Mon Sep 17 00:00:00 2001 From: Josh Bleecher Snyder Date: Wed, 17 May 2017 06:28:03 -0700 Subject: [PATCH] cmd/compile: search for remaining WB ops from end to beginning MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The writebarrier pass processes WB ops from beginning to end, replacing them by other values. But it also checks whether there are more ops to process by walking from beginning to end. This is quadratic, so walk from end to beginning instead. This speeds up compiling the code in issue 13554: name old time/op new time/op delta Pkg 11.9s ± 2% 8.3s ± 3% -29.88% (p=0.000 n=18+17) Updates #13554 Passes toolstash-check. Change-Id: I5f8a872ddc4b783540220d89ea2ee188a6d2b2ff Reviewed-on: https://go-review.googlesource.com/43571 Run-TryBot: Josh Bleecher Snyder TryBot-Result: Gobot Gobot Reviewed-by: Cherry Zhang --- src/cmd/compile/internal/ssa/writebarrier.go | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/src/cmd/compile/internal/ssa/writebarrier.go b/src/cmd/compile/internal/ssa/writebarrier.go index 3443c6464f..cf22724a86 100644 --- a/src/cmd/compile/internal/ssa/writebarrier.go +++ b/src/cmd/compile/internal/ssa/writebarrier.go @@ -261,8 +261,11 @@ func writebarrier(f *Func) { } // if we have more stores in this block, do this block again - for _, w := range b.Values { - if w.Op == OpStoreWB || w.Op == OpMoveWB || w.Op == OpZeroWB { + // check from end to beginning, to avoid quadratic behavior; issue 13554 + // TODO: track the final value to avoid any looping here at all + for i := len(b.Values) - 1; i >= 0; i-- { + switch b.Values[i].Op { + case OpStoreWB, OpMoveWB, OpZeroWB: goto again } } -- 2.50.0