From: David Chase <drchase@google.com>
Date: Mon, 30 Sep 2019 15:10:36 +0000 (-0400)
Subject: cmd/compile: make nilcheck more careful about statement relocations
X-Git-Tag: go1.14beta1~875
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=08a87938bb95ae8859600be20a998fbb4b904915;p=gostls13.git

cmd/compile: make nilcheck more careful about statement relocations

The earlier code was picking nodes that were "poor choices" and
thus sometimes losing statements altogether.

Change-Id: Ibe5ed800ffbd3c926c0ab1bc10c77d72d3042e45
Reviewed-on: https://go-review.googlesource.com/c/go/+/198478
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
---

diff --git a/src/cmd/compile/internal/ssa/nilcheck.go b/src/cmd/compile/internal/ssa/nilcheck.go
index 009c68afa1..9516d58a6e 100644
--- a/src/cmd/compile/internal/ssa/nilcheck.go
+++ b/src/cmd/compile/internal/ssa/nilcheck.go
@@ -153,12 +153,20 @@ func nilcheckelim(f *Func) {
 					work = append(work, bp{op: ClearPtr, ptr: ptr})
 					fallthrough // a non-eliminated nil check might be a good place for a statement boundary.
 				default:
-					if pendingLines.contains(v.Pos) && v.Pos.IsStmt() != src.PosNotStmt {
+					if v.Pos.IsStmt() != src.PosNotStmt && !isPoorStatementOp(v.Op) && pendingLines.contains(v.Pos) {
 						v.Pos = v.Pos.WithIsStmt()
 						pendingLines.remove(v.Pos)
 					}
 				}
 			}
+			// This reduces the lost statement count in "go" by 5 (out of 500 total).
+			for j := 0; j < i; j++ { // is this an ordering problem?
+				v := b.Values[j]
+				if v.Pos.IsStmt() != src.PosNotStmt && !isPoorStatementOp(v.Op) && pendingLines.contains(v.Pos) {
+					v.Pos = v.Pos.WithIsStmt()
+					pendingLines.remove(v.Pos)
+				}
+			}
 			if pendingLines.contains(b.Pos) {
 				b.Pos = b.Pos.WithIsStmt()
 				pendingLines.remove(b.Pos)