[dev.ssa] cmd/compile: implement OCHECKNIL
[dev.ssa] cmd/compile: implement OCHECKNIL

Change-Id: Ifb6b2ad6078ad084b73c0e785e748e92139684e2
Reviewed-on: https://go-review.googlesource.com/14338
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
Run-TryBot: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

4ad/go,Cofyc/go,miolini/go,miolini/go,ganboing/go-esx,golang/go,ImJasonH/go,derekmarcotte/go,nawawi/go,josharian/go,binarycrusader/go,4ad/go,ImJasonH/go,miolini/go,cloudflare/go,CAFxX/go,4ad/go,linux-on-ibm-z/go,vsekhar/elastic-go,vsekhar/elastic-go,golang/go,theif519/go,akutz/go,derekmarcotte/go,momchil-velikov/go,ganboing/go-esx,nawawi/go,CAFxX/go,vanloswang/go,derekmarcotte/go,vsekhar/elastic-go,Samurais/go,derekmarcotte/go,codestation/go,Cofyc/go,goodlang/good,polyverse-security/go,suncycheng/go,ImJasonH/go,suncycheng/go,polyverse-security/go,ImJasonH/go,codestation/go,CAFxX/go,4ad/go,theif519/go,cloudflare/go,theif519/go,golang/go,momchil-velikov/go,ganboing/go-esx,polyverse-security/go,Samurais/go,golang/go,Samurais/go,momchil-velikov/go,vsekhar/elastic-go,Cofyc/go,Cofyc/go,josharian/go,josharian/go,mwhudson/go,ganboing/go-esx,momchil-velikov/go,binarycrusader/go,miolini/go,miolini/go,linux-on-ibm-z/go,polyverse-security/go,nawawi/go,polyverse-security/go,golang/go,josharian/go,binarycrusader/go,4ad/go,mwhudson/go,ImJasonH/go,binarycrusader/go,nawawi/go,suncycheng/go,golang/go,vanloswang/go,ganboing/go-esx,vanloswang/go,ImJasonH/go,goodlang/good,miolini/go,Samurais/go,polyverse-security/go,mwhudson/go,ganboing/go-esx,suncycheng/go,Cofyc/go,4ad/go,ImJasonH/go,binarycrusader/go,theif519/go,theif519/go,vsekhar/elastic-go,suncycheng/go,goodlang/good,Samurais/go,akutz/go,4ad/go,cloudflare/go,vanloswang/go,cloudflare/go,codestation/go,linux-on-ibm-z/go,Cofyc/go,linux-on-ibm-z/go,mwhudson/go,Samurais/go,codestation/go,CAFxX/go,ImJasonH/go,CAFxX/go,derekmarcotte/go,codestation/go,Samurais/go,suncycheng/go,vsekhar/elastic-go,akutz/go,polyverse-security/go,miolini/go,nawawi/go,nawawi/go,momchil-velikov/go,momchil-velikov/go,linux-on-ibm-z/go,nawawi/go,suncycheng/go,Samurais/go,suncycheng/go,derekmarcotte/go,binarycrusader/go,linux-on-ibm-z/go,theif519/go,cloudflare/go,binarycrusader/go,josharian/go,linux-on-ibm-z/go,derekmarcotte/go,nawawi/go,cloudflare/go,goodlang/good,akutz/go,codestation/go,mwhudson/go,akutz/go,ganboing/go-esx,akutz/go,linux-on-ibm-z/go,vanloswang/go,codestation/go,mwhudson/go,CAFxX/go,josharian/go,mwhudson/go,josharian/go,momchil-velikov/go,miolini/go,4ad/go,christopher-henderson/Go,cloudflare/go,cloudflare/go,mwhudson/go,CAFxX/go,theif519/go,vanloswang/go,golang/go,derekmarcotte/go,akutz/go,goodlang/good,Cofyc/go,goodlang/good,Cofyc/go,vanloswang/go,akutz/go,goodlang/good,vsekhar/elastic-go,josharian/go,ganboing/go-esx,binarycrusader/go,golang/go,goodlang/good,theif519/go,vanloswang/go,polyverse-security/go,momchil-velikov/go,vsekhar/elastic-go,CAFxX/go,codestation/go