Add more comments on how dead store elimination works.
Add more comments on how dead store elimination works.

Swift SVN r32538

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