cmd/compile: handle OCONV[NOP] in samesafeexpr
cmd/compile: handle OCONV[NOP] in samesafeexpr

This increases the effectiveness of the
"integer-in-range" CL that follows.

Change-Id: I23b7b6809f0b2c25ed1d59dd2d5429c30f1db89c
Reviewed-on: https://go-review.googlesource.com/27651
Run-TryBot: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

Cofyc/go,goodlang/good,momchil-velikov/go,nawawi/go,polyverse-security/go,nawawi/go,momchil-velikov/go,CAFxX/go,ImJasonH/go,vsekhar/elastic-go,momchil-velikov/go,akutz/go,akutz/go,golang/go,derekmarcotte/go,goodlang/good,polyverse-security/go,akutz/go,goodlang/good,cloudflare/go,Cofyc/go,CAFxX/go,suncycheng/go,codestation/go,momchil-velikov/go,suncycheng/go,nawawi/go,golang/go,polyverse-security/go,suncycheng/go,josharian/go,linux-on-ibm-z/go,ImJasonH/go,derekmarcotte/go,nawawi/go,suncycheng/go,codestation/go,cloudflare/go,josharian/go,golang/go,suncycheng/go,codestation/go,josharian/go,ImJasonH/go,suncycheng/go,goodlang/good,polyverse-security/go,ImJasonH/go,goodlang/good,golang/go,akutz/go,ImJasonH/go,vsekhar/elastic-go,akutz/go,derekmarcotte/go,codestation/go,linux-on-ibm-z/go,vsekhar/elastic-go,akutz/go,CAFxX/go,cloudflare/go,momchil-velikov/go,linux-on-ibm-z/go,vsekhar/elastic-go,vsekhar/elastic-go,nawawi/go,nawawi/go,CAFxX/go,derekmarcotte/go,linux-on-ibm-z/go,cloudflare/go,CAFxX/go,golang/go,akutz/go,golang/go,Cofyc/go,vsekhar/elastic-go,linux-on-ibm-z/go,polyverse-security/go,derekmarcotte/go,akutz/go,momchil-velikov/go,ImJasonH/go,josharian/go,derekmarcotte/go,josharian/go,codestation/go,goodlang/good,polyverse-security/go,momchil-velikov/go,Cofyc/go,linux-on-ibm-z/go,polyverse-security/go,goodlang/good,CAFxX/go,Cofyc/go,Cofyc/go,cloudflare/go,derekmarcotte/go,momchil-velikov/go,cloudflare/go,vsekhar/elastic-go,cloudflare/go,josharian/go,Cofyc/go,linux-on-ibm-z/go,cloudflare/go,golang/go,CAFxX/go,polyverse-security/go,suncycheng/go,codestation/go,codestation/go,golang/go,CAFxX/go,nawawi/go,nawawi/go,josharian/go,ImJasonH/go,ImJasonH/go,josharian/go,codestation/go,derekmarcotte/go,Cofyc/go,christopher-henderson/Go,vsekhar/elastic-go,suncycheng/go,linux-on-ibm-z/go,goodlang/good