From: Russ Cox <rsc@golang.org>
Date: Fri, 4 Dec 2020 04:56:16 +0000 (-0500)
Subject: [dev.regabi] cmd/compile: avoid general traversal in deadcode
X-Git-Tag: go1.17beta1~1539^2~371
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=9ab3d854ad;p=gostls13.git

[dev.regabi] cmd/compile: avoid general traversal in deadcode

deadcode is trying to walk the statements it can find,
but it can sweep in other nodes too. Stop doing that:
only walk known statements containing statements.

Otherwise, if we put panics in expression accessors that
shouldn't be used anymore, deadcode can trip them.

deadcode would be a good candidate to rewrite using
EditChildren, but that would certainly cause toolstash
changes, since deadcode is so ad-hoc about exactly
which parts of the function it looks at. For now just
remove the general traversal and leave as is.

Passes buildall w/ toolstash -cmp.

Change-Id: I06481eb87350905597600203c4fa724d55645b46
Reviewed-on: https://go-review.googlesource.com/c/go/+/275377
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
---

diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index 65c5f2abce..2070297bc0 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -3860,9 +3860,24 @@ func deadcodeslice(nn *ir.Nodes) {
 		}
 
 		deadcodeslice(n.PtrInit())
-		deadcodeslice(n.PtrBody())
-		deadcodeslice(n.PtrList())
-		deadcodeslice(n.PtrRlist())
+		switch n.Op() {
+		case ir.OBLOCK:
+			deadcodeslice(n.PtrList())
+		case ir.OCASE:
+			deadcodeslice(n.PtrBody())
+		case ir.OFOR:
+			deadcodeslice(n.PtrBody())
+		case ir.OIF:
+			deadcodeslice(n.PtrBody())
+			deadcodeslice(n.PtrRlist())
+		case ir.ORANGE:
+			deadcodeslice(n.PtrBody())
+		case ir.OSELECT:
+			deadcodeslice(n.PtrList())
+		case ir.OSWITCH:
+			deadcodeslice(n.PtrList())
+		}
+
 		if cut {
 			nn.Set(nn.Slice()[:i+1])
 			break