Runtime performance: avoid llvm::RoundUpToAlignment(size, mask + 1)
Runtime performance: avoid llvm::RoundUpToAlignment(size, mask + 1)

If we have a power-of-two mask, we don't need to bother with arbitrary
size alignment and the integer division fallout.

Swift SVN r14097

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