Explain why we remove the underflow check.
Explain why we remove the underflow check.

Swift SVN r25825

Ivacker/swift,hooman/swift,tinysun212/swift-windows,xedin/swift,xedin/swift,slavapestov/swift,jopamer/swift,harlanhaskins/swift,tjw/swift,bitjammer/swift,alblue/swift,kperryua/swift,jopamer/swift,allevato/swift,devincoughlin/swift,CodaFi/swift,danielmartin/swift,ken0nek/swift,gottesmm/swift,brentdax/swift,natecook1000/swift,mightydeveloper/swift,danielmartin/swift,alblue/swift,IngmarStein/swift,emilstahl/swift,arvedviehweger/swift,CodaFi/swift,bitjammer/swift,karwa/swift,xedin/swift,SwiftAndroid/swift,amraboelela/swift,kentya6/swift,zisko/swift,atrick/swift,roambotics/swift,cbrentharris/swift,kusl/swift,gottesmm/swift,calebd/swift,airspeedswift/swift,shajrawi/swift,djwbrown/swift,JGiola/swift,jtbandes/swift,gottesmm/swift,nathawes/swift,huonw/swift,hooman/swift,adrfer/swift,brentdax/swift,danielmartin/swift,hughbe/swift,jtbandes/swift,ben-ng/swift,JaSpa/swift,kperryua/swift,parkera/swift,austinzheng/swift,practicalswift/swift,LeoShimonaka/swift,kperryua/swift,modocache/swift,return/swift,airspeedswift/swift,stephentyrone/swift,swiftix/swift,swiftix/swift.old,hooman/swift,johnno1962d/swift,kusl/swift,roambotics/swift,JGiola/swift,practicalswift/swift,therealbnut/swift,gribozavr/swift,arvedviehweger/swift,gregomni/swift,austinzheng/swift,OscarSwanros/swift,huonw/swift,modocache/swift,JGiola/swift,kstaring/swift,devincoughlin/swift,lorentey/swift,lorentey/swift,felix91gr/swift,arvedviehweger/swift,allevato/swift,SwiftAndroid/swift,russbishop/swift,natecook1000/swift,johnno1962d/swift,cbrentharris/swift,ahoppen/swift,frootloops/swift,jckarter/swift,slavapestov/swift,gmilos/swift,kstaring/swift,dduan/swift,SwiftAndroid/swift,rudkx/swift,codestergit/swift,swiftix/swift,aschwaighofer/swift,hughbe/swift,MukeshKumarS/Swift,dduan/swift,felix91gr/swift,zisko/swift,gottesmm/swift,tjw/swift,shahmishal/swift,russbishop/swift,rudkx/swift,arvedviehweger/swift,khizkhiz/swift,SwiftAndroid/swift,JaSpa/swift,tinysun212/swift-windows,swiftix/swift.old,sschiau/swift,devincoughlin/swift,karwa/swift,LeoShimonaka/swift,alblue/swift,khizkhiz/swift,frootloops/swift,airspeedswift/swift,bitjammer/swift,brentdax/swift,slavapestov/swift,gmilos/swift,calebd/swift,nathawes/swift,kperryua/swift,manavgabhawala/swift,airspeedswift/swift,alblue/swift,kstaring/swift,OscarSwanros/swift,airspeedswift/swift,tardieu/swift,codestergit/swift,cbrentharris/swift,lorentey/swift,djwbrown/swift,calebd/swift,brentdax/swift,hughbe/swift,milseman/swift,kperryua/swift,kentya6/swift,CodaFi/swift,milseman/swift,swiftix/swift.old,kentya6/swift,deyton/swift,manavgabhawala/swift,KrishMunot/swift,shahmishal/swift,kusl/swift,swiftix/swift,emilstahl/swift,aschwaighofer/swift,arvedviehweger/swift,gribozavr/swift,gottesmm/swift,sschiau/swift,shajrawi/swift,nathawes/swift,xwu/swift,Ivacker/swift,therealbnut/swift,cbrentharris/swift,benlangmuir/swift,bitjammer/swift,swiftix/swift.old,OscarSwanros/swift,dduan/swift,ben-ng/swift,kstaring/swift,emilstahl/swift,gottesmm/swift,jmgc/swift,dduan/swift,Ivacker/swift,return/swift,brentdax/swift,jckarter/swift,allevato/swift,therealbnut/swift,hughbe/swift,IngmarStein/swift,zisko/swift,allevato/swift,djwbrown/swift,natecook1000/swift,shahmishal/swift,shajrawi/swift,glessard/swift,mightydeveloper/swift,kusl/swift,karwa/swift,aschwaighofer/swift,amraboelela/swift,ahoppen/swift,therealbnut/swift,KrishMunot/swift,Ivacker/swift,gregomni/swift,MukeshKumarS/Swift,benlangmuir/swift,kentya6/swift,tkremenek/swift,harlanhaskins/swift,KrishMunot/swift,djwbrown/swift,djwbrown/swift,swiftix/swift.old,JGiola/swift,shahmishal/swift,milseman/swift,gmilos/swift,hooman/swift,dduan/swift,lorentey/swift,benlangmuir/swift,kentya6/swift,devincoughlin/swift,karwa/swift,modocache/swift,modocache/swift,JaSpa/swift,practicalswift/swift,apple/swift,devincoughlin/swift,apple/swift,alblue/swift,tardieu/swift,jckarter/swift,slavapestov/swift,calebd/swift,shahmishal/swift,jtbandes/swift,swiftix/swift.old,milseman/swift,huonw/swift,rudkx/swift,tkremenek/swift,tkremenek/swift,tardieu/swift,parkera/swift,amraboelela/swift,jopamer/swift,ben-ng/swift,huonw/swift,adrfer/swift,OscarSwanros/swift,gribozavr/swift,kentya6/swift,gmilos/swift,djwbrown/swift,austinzheng/swift,nathawes/swift,johnno1962d/swift,jmgc/swift,alblue/swift,glessard/swift,swiftix/swift,stephentyrone/swift,tardieu/swift,LeoShimonaka/swift,glessard/swift,return/swift,danielmartin/swift,tjw/swift,stephentyrone/swift,Jnosh/swift,frootloops/swift,adrfer/swift,deyton/swift,kperryua/swift,sschiau/swift,nathawes/swift,LeoShimonaka/swift,practicalswift/swift,dreamsxin/swift,mightydeveloper/swift,ken0nek/swift,practicalswift/swift,harlanhaskins/swift,frootloops/swift,jtbandes/swift,cbrentharris/swift,manavgabhawala/swift,xwu/swift,khizkhiz/swift,xedin/swift,atrick/swift,parkera/swift,ben-ng/swift,jmgc/swift,codestergit/swift,xedin/swift,sschiau/swift,allevato/swift,uasys/swift,adrfer/swift,arvedviehweger/swift,kstaring/swift,karwa/swift,khizkhiz/swift,SwiftAndroid/swift,tkremenek/swift,roambotics/swift,codestergit/swift,bitjammer/swift,natecook1000/swift,mightydeveloper/swift,huonw/swift,ken0nek/swift,JaSpa/swift,xwu/swift,LeoShimonaka/swift,IngmarStein/swift,khizkhiz/swift,uasys/swift,brentdax/swift,jmgc/swift,russbishop/swift,therealbnut/swift,tardieu/swift,emilstahl/swift,atrick/swift,adrfer/swift,hughbe/swift,lorentey/swift,ahoppen/swift,kusl/swift,swiftix/swift,slavapestov/swift,devincoughlin/swift,khizkhiz/swift,xwu/swift,MukeshKumarS/Swift,milseman/swift,roambotics/swift,kusl/swift,allevato/swift,stephentyrone/swift,hooman/swift,deyton/swift,danielmartin/swift,Ivacker/swift,jtbandes/swift,tkremenek/swift,stephentyrone/swift,JaSpa/swift,harlanhaskins/swift,deyton/swift,xedin/swift,modocache/swift,swiftix/swift,sdulal/swift,slavapestov/swift,zisko/swift,codestergit/swift,dreamsxin/swift,emilstahl/swift,aschwaighofer/swift,kusl/swift,shajrawi/swift,russbishop/swift,tjw/swift,JaSpa/swift,djwbrown/swift,parkera/swift,IngmarStein/swift,amraboelela/swift,xwu/swift,alblue/swift,bitjammer/swift,tjw/swift,arvedviehweger/swift,atrick/swift,benlangmuir/swift,practicalswift/swift,ahoppen/swift,sdulal/swift,kentya6/swift,harlanhaskins/swift,felix91gr/swift,brentdax/swift,therealbnut/swift,sdulal/swift,slavapestov/swift,parkera/swift,kstaring/swift,kusl/swift,KrishMunot/swift,austinzheng/swift,codestergit/swift,amraboelela/swift,hooman/swift,huonw/swift,swiftix/swift.old,ahoppen/swift,apple/swift,gmilos/swift,johnno1962d/swift,frootloops/swift,jtbandes/swift,jckarter/swift,gregomni/swift,gribozavr/swift,shajrawi/swift,karwa/swift,apple/swift,gregomni/swift,khizkhiz/swift,tkremenek/swift,tinysun212/swift-windows,tinysun212/swift-windows,ahoppen/swift,Ivacker/swift,mightydeveloper/swift,modocache/swift,ken0nek/swift,practicalswift/swift,felix91gr/swift,lorentey/swift,MukeshKumarS/Swift,MukeshKumarS/Swift,ken0nek/swift,rudkx/swift,allevato/swift,benlangmuir/swift,jmgc/swift,austinzheng/swift,harlanhaskins/swift,xedin/swift,swiftix/swift.old,jtbandes/swift,gribozavr/swift,Jnosh/swift,calebd/swift,gregomni/swift,tjw/swift,manavgabhawala/swift,kentya6/swift,JGiola/swift,LeoShimonaka/swift,LeoShimonaka/swift,xedin/swift,aschwaighofer/swift,bitjammer/swift,Ivacker/swift,karwa/swift,frootloops/swift,jopamer/swift,danielmartin/swift,uasys/swift,atrick/swift,tjw/swift,parkera/swift,deyton/swift,mightydeveloper/swift,codestergit/swift,practicalswift/swift,jckarter/swift,johnno1962d/swift,felix91gr/swift,SwiftAndroid/swift,deyton/swift,sschiau/swift,mightydeveloper/swift,gmilos/swift,stephentyrone/swift,Jnosh/swift,nathawes/swift,emilstahl/swift,ken0nek/swift,Jnosh/swift,calebd/swift,gribozavr/swift,CodaFi/swift,uasys/swift,ben-ng/swift,natecook1000/swift,IngmarStein/swift,jmgc/swift,gregomni/swift,jopamer/swift,deyton/swift,CodaFi/swift,devincoughlin/swift,huonw/swift,harlanhaskins/swift,shahmishal/swift,xwu/swift,shajrawi/swift,return/swift,sschiau/swift,amraboelela/swift,manavgabhawala/swift,ken0nek/swift,austinzheng/swift,cbrentharris/swift,OscarSwanros/swift,shajrawi/swift,glessard/swift,uasys/swift,danielmartin/swift,rudkx/swift,natecook1000/swift,gribozavr/swift,atrick/swift,sschiau/swift,CodaFi/swift,jopamer/swift,Jnosh/swift,sdulal/swift,uasys/swift,roambotics/swift,tkremenek/swift,felix91gr/swift,hooman/swift,swiftix/swift,emilstahl/swift,sdulal/swift,IngmarStein/swift,mightydeveloper/swift,zisko/swift,airspeedswift/swift,lorentey/swift,lorentey/swift,cbrentharris/swift,MukeshKumarS/Swift,tinysun212/swift-windows,shahmishal/swift,KrishMunot/swift,sdulal/swift,return/swift,milseman/swift,airspeedswift/swift,MukeshKumarS/Swift,milseman/swift,KrishMunot/swift,tardieu/swift,apple/swift,emilstahl/swift,jckarter/swift,russbishop/swift,therealbnut/swift,karwa/swift,KrishMunot/swift,parkera/swift,JaSpa/swift,IngmarStein/swift,aschwaighofer/swift,dduan/swift,LeoShimonaka/swift,natecook1000/swift,CodaFi/swift,kstaring/swift,gottesmm/swift,roambotics/swift,jopamer/swift,zisko/swift,adrfer/swift,zisko/swift,ben-ng/swift,Jnosh/swift,calebd/swift,russbishop/swift,shajrawi/swift,return/swift,stephentyrone/swift,benlangmuir/swift,manavgabhawala/swift,tinysun212/swift-windows,xwu/swift,tardieu/swift,johnno1962d/swift,devincoughlin/swift,jckarter/swift,JGiola/swift,johnno1962d/swift,SwiftAndroid/swift,adrfer/swift,glessard/swift,glessard/swift,cbrentharris/swift,OscarSwanros/swift,sschiau/swift,sdulal/swift,shahmishal/swift,gribozavr/swift,ben-ng/swift,parkera/swift,frootloops/swift,felix91gr/swift,tinysun212/swift-windows,russbishop/swift,sdulal/swift,hughbe/swift,dduan/swift,OscarSwanros/swift,return/swift,rudkx/swift,kperryua/swift,modocache/swift,amraboelela/swift,gmilos/swift,Ivacker/swift,manavgabhawala/swift,aschwaighofer/swift,nathawes/swift,jmgc/swift,hughbe/swift,Jnosh/swift,uasys/swift,apple/swift,austinzheng/swift