cmd/compile: optimize noding of long summation expressions
cmd/compile: optimize noding of long summation expressions

Fixes #16394.

Change-Id: I7108c9e8e67d86678bdb6015f0862e5c92bcf911
Reviewed-on: https://go-review.googlesource.com/76450
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

golang/go,akutz/go,cloudflare/go,nawawi/go,CAFxX/go,nawawi/go,josharian/go,golang/go,golang/go,Cofyc/go,josharian/go,golang/go,Cofyc/go,josharian/go,nawawi/go,codestation/go,codestation/go,Cofyc/go,Cofyc/go,Cofyc/go,CAFxX/go,nawawi/go,cloudflare/go,CAFxX/go,cloudflare/go,codestation/go,CAFxX/go,Cofyc/go,CAFxX/go,golang/go,CAFxX/go,codestation/go,golang/go,akutz/go,akutz/go,codestation/go,nawawi/go,CAFxX/go,josharian/go,cloudflare/go,akutz/go,golang/go,nawawi/go,cloudflare/go,christopher-henderson/Go,codestation/go,akutz/go,golang/go,codestation/go,cloudflare/go,CAFxX/go,akutz/go,cloudflare/go,josharian/go,cloudflare/go,akutz/go,codestation/go,Cofyc/go,akutz/go,josharian/go,nawawi/go,Cofyc/go,josharian/go,nawawi/go,josharian/go