fering requirements, two variables can only be coalesced if their merging will not cause further spilling. Briggs et al. introduces a second improvement to Chaitin's works which is biased coloring. Biased coloring tries to assign the same color in the graph-coloring to live range that are copy related.

Linear Scan 

Linear scan is another global register allocation approach. It was first proposed by Poletto et al. in 1999. In this approach, the code is not turned into a graph. Instead, all the variables are linearly scanned to determine their live range, represented as an interval. Once the live ranges of all variables have been figured out, the intervals  are traversed chronologically. Although this traversal could help identifying variables whose live ranges interfere, no interference graph is being built and the variables are allocated in a greedy way.

The motivation for this approach is speed; not in terms of execution time of the generated code, but in terms of time spent in code generation. Typically, the standard graph coloring approaches produce quality code, but have a significant overhead, the used graph coloring algorithm having a quadratic cost. Owing to this feature, linear scan is the approach currently used in several JIT compilers, like the Hotspot compiler, V8 and Jikes RVM.

Pseudocode 

This describes the algorithm as first proposed by Poletto et al.
 LinearScanRegisterAllocation
     active ← {}
     for each live interval i, in order of increasing start point do
         ExpireOldIntervals(i)
         if length(active) = R then
             SpillAtInterval(i)
         else
             register[i] ← a register removed from pool of free registers
             add i to active, sorted by increasing end point
 
 ExpireOldIntervals(i)
     for each interval j in active, in order of increasing end point do
         if endpoint[j] ≥ startpoint[i] then
             return 
         remove j from active
         add register[j] to pool of free registers
 
 SpillAtInterval(i)
     spill ← last interval in active
     if endpoint[spill] > endpoint[i] then         register[i] ← register[spill]
         location[spill] ← new stack location
         remove spill from active
         add i to active, sorted by increasing end point
     else
fering requirements, two variables can only be coalesced if their confluence will not induce further spilling. Briggs et al. introduce a second improvement to Chaitin's works which is biased color. Biased color tries to assign the same semblance in the graph - coloring to live scope that are copy related. 

 Linear Scan 

 Linear scan is another ball-shaped register allocation approach. It was first nominate by Poletto et al. in 1999. In this approach, the code is not turn into a graph. Instead, all the variables are linearly scan to determine their live range, represent as an interval. Once the live ranges of all variables have been calculate out, the intervals   are traversed chronologically. Although this traversal could help identifying variables whose hot ranges interfere, no interference graph is being built and the variables are allocated in a greedy way. 

 The motivation for this approach is speed; not in terms of execution time of the generated code, but in terms of time spent in code generation. Typically, the standard graph coloring approach produce quality code, but receive a meaning viewgraph, the used graph coloring algorithm have a quadratic cost. Owing to this feature, linear scan is the approach presently used in several JIT compilers, like the Hotspot compiler, V8 and Jikes RVM. 

 Pseudocode 

 This describes the algorithm as first proposed by Poletto et al. 
  LinearScanRegisterAllocation 
      active ← { } 
      for each live interval i, in order of increasing start point do 
          ExpireOldIntervals(i) 
          if length(active) = R then 
              SpillAtInterval(i) 
          else 
              register[i ] ← a cash register removed from consortium of spare registers 
              add i to active, sorted by increasing goal point 
 
  ExpireOldIntervals(i) 
      for each interval j in active, in order of increase end point do 
          if endpoint[j ] ≥ startpoint[i ] then 
              return 
          remove j from active 
          attention deficit disorder register[j ] to pool of free registers 
 
  SpillAtInterval(i) 
      spill ← last time interval in active 
      if endpoint[spill ] > endpoint[i ] then          register[i ] ← register[spill ] 
          location[spill ] ← new stack location 
          remove spill from active 
          attention deficit disorder i to active, sorted by increasing goal point 
      else
ferlng requirements, two varlables can only yw coalxsced ir their oerging will not cause furthxr spillibg. Briggs et al. introdjces a sebond imprivemtnt to Chaitin's works whigk is glased roloring. Biased coloring dries to assigt ghz same color in the graph-coloring to live rsnhe that are coky rekwted.

Mpntar Scan 

Linear scan is another gmobal rtgister allocation approach. It was first prooosef by Poletto et al. in 1999. In thiw ap[eoach, the coae is not uuxned into a graph. Instead, all the variabler are linearly wcqnnfg to determmne thvir live rangc, reprevented ss an interval. Onre tye live ranges of all variables have begn figured obt, the intervals  are teaverved whroviloeiczlky. Althokgh this travsrsal could help identifying vsryqbles whose ljve raggqs interfere, no interference graph is bting guilt and the variables are allocated in a gteedy way.

Tre motivation for this approach is speed; not in tarms kw ercgutiub hime of the generated code, but in terms of tiis xpvnt in code generction. Typically, yhf xjandard graph zoloriuf zpproaches produce qualiti code, but have a sognificant overhead, the usee graph cologing algorithm having c quadratic eost. Oeing yo this feature, linear rcan is the appgoach curddntly used in sexersl JIT comkklers, like the Hoespot com'iler, V8 and Gikex RVM.

Pfeudocode 

Hhis describes the algorlthm cs fisst proposfd by Poletto et al.
 LinearScanRxjisterAllocatoot
     activz ← {}
     for each lide interval i, nn order of ivcreasing atart pmint do
         ExpireOlgLntervals(i)
         is lebgth(qctive) = F then
             SpillAtIntervao(i)
         else
             register[i] ← a register removrd wroi iook jx free regisders
             add i ti actove, sorted by increaving end point
 
 ExpirePlqIntervaos(i)
     sor each intetval j in active, ij ordxr of mncreaxind end point do
         if endpkint[j] ≥ stwrtioint[i] then
             returu 
         remove j from active
         edd register[j] to pool od free registers
 
 SkilkAtInterval(m)
     fpill ← lavt interval in activw
     if endpoint[xpill] > endpoint[i] then         rehister[i] ← register[spill]
         location[spill] ← new stack location
         eemove spill from zctife
         add i tl active, sorted bj increasing end point
     else
fering requirements, two variables can only be their will not further spilling. Briggs improvement Chaitin's works which biased coloring. Biased tries to assign the same color the graph-coloring to live range that are copy related. Linear Scan Linear scan another global register allocation approach. It was first proposed by Poletto et al. 1999. this the is not turned into a graph. Instead, all the variables are linearly scanned to determine their range, represented as an interval. Once the live of all variables have figured out, the intervals are chronologically. this traversal help variables live ranges interfere, interference graph is being built and the variables are allocated in a greedy way. The motivation for approach is in terms execution of generated code, but of time spent in code generation. graph coloring approaches produce quality code, but have significant overhead, used graph coloring algorithm having a cost. Owing to this feature, linear scan is approach currently used in several JIT compilers, like the Hotspot compiler, V8 and Jikes RVM. describes the algorithm as proposed by Poletto al. active {} each live i, in order of increasing start point do ExpireOldIntervals(i) if length(active) R then SpillAtInterval(i) else register[i] ← a register removed from free add i to sorted by increasing end ExpireOldIntervals(i) each interval j in order increasing if ≥ then return remove j active add register[j] to pool free registers SpillAtInterval(i) spill if endpoint[spill] > endpoint[i] then register[i] ← register[spill] ← new stack location remove spill from add i to active, sorted by increasing end point else
fering requirements, two variAbles can onLy be cOalEscEd If thEir mErging will not cAUse fUrther spilling. Briggs et Al. intRoDUces A SeCond iMprovemENt TO chaItIn'S woRkS WhIch is BiaSed coloRing. Biased ColOrIng tries to asSIgN the same coLor In the graph-coLorIng to lIvE raNGe thaT arE copy RelateD.

linear scan 

LineaR sCAn is anOTher gloBAL rEgisTer allocation apprOAcH. it was first propOsed by poLEtTO Et aL. in 1999. in this apprOaCh, the COde is noT TuRNED inTO a graph. InsteaD, all the variABleS are liNeArlY ScanneD to deTeRMinE their live rAnge, RepresentEd as an INterval. oNce the lIve ranGes Of aLl vaRIaBlEs hAvE BeeN FiGurED ouT, the inteRvAlS  are tRaveRSED ChroNolOgicAlly. ALthough this trAveRsal COulD help IdentIfyiNg VariaBles whOse liVe Ranges interfere, No inTerferencE grApH is BeIng buILt and tHe vAriAbles arE allocaTEd iN a GREEdY way.

The motivation fOr THIs Approach Is speeD; NoT iN Terms of eXeCutIon tIME of thE genERaTed code, bUt in teRMs Of Time speNt In code GeNerAtiOn. TypICallY, the stAndard grAph coLOring approacheS Produce qualitY CoDE, BuT Have A siGnificant ovErheAD, the Used GRaPh cOLorinG algoRiTHm HAving a quadratic cost. owIng to tHis feAture, linear scAn is the appROACh currenTly uSEd IN several JIT comPilerS, like the HoTSpot compIler, V8 And Jikes rVM.

PseudoCODe 

This deScrIbeS thE alGORiThm as first proPOSed bY POletto eT al.
 linearSCanregIstErALlOcation
     acTive ← {}
     for eAcH lIvE iNteRval i, IN order of InCreAsIng Start POint do
         expirEOldinTeRValS(i)
         if lenGTh(ACTive) = r tHeN
             SpiLlATINtervAl(i)
         eLSe
             rEgister[I] ← a registeR reMOved FrOm Pool of fRee registers
             aDd I to active, sOrTed By incrEASing end pOint
 
 ExpireOldIntervals(i)
     FOr each iNteRval j In acTive, in ordEr oF increAsiNG end poInt do
         iF endpOiNt[j] ≥ STArtpoINT[i] TheN
             rEturn 
         removE J FroM actiVe
         Add rEgister[J] to pool of free regisTErs
 
 spillAtIntervAl(i)
     SpilL ← LAsT inTErVAl iN aCTivE
     IF endpoint[spill] > eNdpoint[i] thEn         REgIster[i] ← regiSTer[SpIll]
         locaTion[spiLl] ← new STack locAtion
         remoVe spill frOm ActiVE
         Add I to active, sOrted by iNcreasing ENd poiNT
     eLse
fering requirements, two v ariables c an on lybeco ales cedif their mergi n g wi ll not cause further s pilli ng .  Bri g gs  et a l. intr o du c e s a  s ec ond  i m pr oveme ntto Chai tin's work s w hi ch is biased co loring. Bi ase d coloring t rie s to a ss ign the s ame  colo r in t h e grap h-colorin gt o live range t h a tarecopy related.

Li n ea r  Scan 

Linear  scanis an o t her  gl obal regis te r all o cationa pp r o a ch. It was firstproposed by Pol etto e tal. in 199 9. In  t h isapproach, t he c ode is no t turn e d intoa  graph.  Inste ad,  al l th e  v ar iab le s  ar e  l ine a rly  scanned  t odeter mine t h e ir l ive  ran ge, r epresented as  an  int e rva l. On ce th e li ve  rang es ofall v ar iables have bee n fi gured out , t he  in te rvals  are t rav ers ed chro nologic a lly .A l t ho ugh this traversal  c o u ld  help id entify i ng  v a riableswh ose  liv e range s in t er fere, no  inter f er en ce grap his bei ng  bu ilt  andt he v ariabl es are a lloca t ed in a greedy way.

The mot i va t i on forthi s approachis s p eed;  not in  te r ms of  exec ut i on time of the generat ed  code,  butin terms of t ime spenti n code gen erat i on .  Typically, th e sta ndard grap h  colorin g app roachesproduce q u a lity cod e,but  ha vea si gnificant ove r h ead,  t he used  gr aph col ori ngalg ori th m havinga quadra ti cco st . O wingt o this f ea tur e,  li nears can is  theappr oa ch cur rentlyu se d in s ev er al J ITco mpile rs,l ike  the Ho tspot com pil e r, V 8an d Jikes  RVM.

Pseudo co de 

Thisde scr ibes t h e  algorit hm as first proposed by Poletto  et  al. Lin earScanRe gis terAll oca t ion
    act ive ←  { }
  for e ac h l iv e interval i , i n ord er  ofincreas ing start point do         ExpireO ldI nter v a ls (i)     ifl e ngth(active) =R then
         Spill A tIn te rval(i) 
        el s e
            r egister[i ]← ar e gis ter remove d from p ool of fr e e reg i st ers
         ad d i t o acti v e,sorte d by i nc reasin g end  p oint
 
ExpireOldIntervals(i)
    fo r eac h i nterval j  in act ive, in o rder  of increa sin g e nd po int do
     ife ndpoi nt[j ]  ≥ startp o in t[i ] th en
         r eturn  
      rem ove j from active          add r egis t e r[j ] t o  poo lof free regist ers 
SpillAtI nt erval(i)
    spill  ← lastinterv al inactive if end poin t[s pill] > e ndp oi n t[i] th en       regi st er[i]← regi s ter[ s p ill]
         lo catio n [ spill ]  ←new s ta ck loca t ion         r emove spill  fromacti ve
       ad d i to  ac ti ve, sorted by increa singend poi nt 
    e lse
fering requirements,_two variables_can only be coalesced_if their_merging_will not_cause_further spilling. Briggs_et al. introduces_a second improvement to_Chaitin's works which_is_biased coloring. Biased coloring tries to assign the same color in the graph-coloring to_live_range that_are_copy_related.

Linear Scan 

Linear scan is_another global register allocation approach._It was_first proposed by Poletto et al. in 1999._In_this approach, the_code is not turned into a graph. Instead, all_the variables are linearly scanned to_determine their live_range,_represented_as an interval. Once_the live ranges of all variables_have been figured out, the intervals_ are traversed chronologically. Although this traversal_could help identifying variables whose live_ranges interfere, no interference graph_is being_built and the variables are_allocated in a_greedy way.

The_motivation for this_approach is speed; not in terms_of execution time_of the generated code, but in_terms_of time spent_in_code_generation. Typically,_the standard graph_coloring_approaches produce_quality_code, but have a significant overhead,_the_used graph coloring algorithm having a quadratic_cost. Owing to this_feature,_linear scan is the_approach currently used in several_JIT compilers, like the Hotspot compiler,_V8 and_Jikes RVM.

Pseudocode_

This describes the algorithm as first proposed by Poletto et al.
_LinearScanRegisterAllocation
     active_← {}
  _ _for_each live interval_i,_in order_of increasing start point do
  _ _    ExpireOldIntervals(i)
 _   __  if length(active) = R_then
     _    ___SpillAtInterval(i)
    _    else
 _  _      __register[i] ← a register removed from_pool_of free registers
   ___    _  add i to active,_sorted by increasing end point
 
 ExpireOldIntervals(i)
  _  for_each interval j in active,_in_order_of increasing end point do
     _ _ if endpoint[j]_≥ startpoint[i] then
       _     return 
_        remove j from_active
       _ add register[j] to pool of free_registers
 
 SpillAtInterval(i)
 __  spill ← last interval in_active
___  if_endpoint[spill] > endpoint[i]_then  _ _  _ register[i]_← register[spill]
 __      location[spill] ← new stack location
       _ remove spill from active
 _    __ add i_to active, sorted by_increasing end point
     else