From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Mon, 15 Mar 2021 23:15:23 +0000 (-0700)
Subject: runtime: incorporate hbits advancement in scanobject into loop
X-Git-Tag: go1.17beta1~659
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=72483de87a36969f0c4d6f01db19f769c8e16e82;p=gostls13.git

runtime: incorporate hbits advancement in scanobject into loop

This makes it clearer that i and hbits advance together.
As a bonus, it generates slightly better code.

Change-Id: I24d51102535c39f962a59c1a4a7c5c894339aa18
Reviewed-on: https://go-review.googlesource.com/c/go/+/309569
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
---

diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index 45ccc806bd..cb73caf3bb 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -1257,12 +1257,7 @@ func scanobject(b uintptr, gcw *gcWork) {
 	}
 
 	var i uintptr
-	for i = 0; i < n; i += sys.PtrSize {
-		// Find bits for this word.
-		if i != 0 {
-			// Avoid needless hbits.next() on last iteration.
-			hbits = hbits.next()
-		}
+	for i = 0; i < n; i, hbits = i+sys.PtrSize, hbits.next() {
 		// Load bits once. See CL 22712 and issue 16973 for discussion.
 		bits := hbits.bits()
 		if bits&bitScan == 0 {