ssa perf 4
ssa perf 4

Summary: Rather than keeping parallel `value_ref` and `havoc` environments, why not "zip" them?

Reviewed By: samwgoldman

Differential Revision: D5948924

fbshipit-source-id: ed1812f4fbd9e4f579b3a705e4048128c7ba7062

popham/flow,samwgoldman/flow,mroch/flow,gabelevi/flow,nmote/flow,mroch/flow,jamesgpearce/flow,claudiopro/flow,claudiopro/flow,nmote/flow,JonathanUsername/flow,popham/flow,MichaelDeBoey/flow,nmote/flow,ylu1317/flow,facebook/flow,mroch/flow,MichaelDeBoey/flow,popham/flow,gabelevi/flow,jamesgpearce/flow,popham/flow,samwgoldman/flow,mroch/flow,facebook/flow,popham/flow,gabelevi/flow,samwgoldman/flow,claudiopro/flow,JonathanUsername/flow,AgentME/flow,JonathanUsername/flow,gabelevi/flow,samwgoldman/flow,AgentME/flow,nmote/flow,gabelevi/flow,mroch/flow,facebook/flow,ylu1317/flow,samwgoldman/flow,ylu1317/flow,jamesgpearce/flow,mroch/flow,facebook/flow,TiddoLangerak/flow,JonathanUsername/flow,ylu1317/flow,TiddoLangerak/flow,mroch/flow,JonathanUsername/flow,facebook/flow,TiddoLangerak/flow,popham/flow,nmote/flow,gabelevi/flow,popham/flow,nmote/flow,claudiopro/flow,samwgoldman/flow,TiddoLangerak/flow,facebook/flow,jamesgpearce/flow,nmote/flow,MichaelDeBoey/flow,claudiopro/flow,jamesgpearce/flow,samwgoldman/flow,AgentME/flow,gabelevi/flow,facebook/flow,jamesgpearce/flow,JonathanUsername/flow,MichaelDeBoey/flow,MichaelDeBoey/flow,AgentME/flow,TiddoLangerak/flow,jamesgpearce/flow,AgentME/flow,JonathanUsername/flow,ylu1317/flow