[dev.ssa] cmd/compile/ssa: handle loops that don't loop
[dev.ssa] cmd/compile/ssa: handle loops that don't loop

Loops such as

func f(c chan int) int {
	for x := range c {
		return x
	}
	return 0
}

don't loop. Remove the assumption that they must.

Partly fixes the build.

Change-Id: I766cebeec8e36d14512bea26f54c06c8eaf95e23
Reviewed-on: https://go-review.googlesource.com/11876
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

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