[dev.ssa] cmd/compile: remove redundant compare ops
[dev.ssa] cmd/compile: remove redundant compare ops

Flagalloc was recalculating flags is some situations
when it didn't need to.  Fixed by using the same name
for the original flag calculation instruction throughout.

Change-Id: Ic0bf58f728a8d87748434dd25a67b0708755e1f8
Reviewed-on: https://go-review.googlesource.com/19237
Run-TryBot: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
Reviewed-by: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>

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