Outline. Tiling, formally. Expression tile as rule. Statement tiles as rules. Function calls. CS 412 Introduction to Compilers

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1 CS 412 Introduction to Compilers Andrew Myers Cornell University Lectur8 Finishing genertion 9 Mr 01 Outline Tiling s syntx-directed trnsltion Implementing function clls Implementing functions Optimizing wy the pointer Dynmiclly-llocted structures strings nd rrys Register lloction the esy wy 2 Tiling, formlly Ech tile is relly n inference rule! Write e c (reg t) for c is vlid for IR expression e tht puts result into t Write s c for c is vlid for IR sttement s Trnsltion is not function of e/s mny possible trnsltions (unlike 6 e, 5 e, etc.) trnsltion reltion generlizes trnsltion function cn pply to erlier trnsltions too but less pyoff 3 Expression tile s rule t f ADD t 1 t 2 mov t f, t 1 dd t f, t 2 c 1 (reg t 1 ) e 2 c 2 (reg t 2 ) ADD(, e 2 ) c 1 ; c 2 ; mov t f, t 1 ; dd t f, t 2 (reg t f ) 4 Sttement tiles s rules c 1 (reg t 1 ) e 2 c 2 (reg t 2 ) (( ), e 2 ) c 1 ; c 2 ; mov [t 1 ], t 2 Function clls How to generte for function clls? Two kinds of IR sttements in cnonicl form t 1 t 2, e 2 op 1 (r/m32) + (, e 2 + CONST(k)) dd op 1, k CONST(k) r/m32 dest f EXP f Inference rules rot syntx-directed need heuristic or dynmic progrmming to choose 5 6 1

2 old Stck lyout current old current new dest f non-risc push push dd e, 4*n Two trnsltions RISC bp old ebp sub e, 4*n mov [e + 4],... mov [e + 4*n], dd e, 4*n 7 8? f Tiling cll push push dd e, 4*n Approch 1 don t fold e i into tile Downside genertes lot of extr temporries Approch 2 try to mtch e i ginst r/m32, tile e i seprtely if filure f push t n push t 1 dd e, 4*n Compiling function bodies How we compiled function body 5Z f () T = e [ = SEQ((RV, -Z e [), LABEL(epilogue)) 5Z f () = e [ = SEQ(EXP(-Z e [), LABEL(epilogue)) Vribles -Z v [ = TEMP(t v ) for -Z v [ = (TEMP(FP) + (4*i+4)) for rg. i -Z v [ = (NAME(v)) for globls Try it out f(x int, yint) = x + y 9 10 Abstrct ssembly for f f(x int, yint) = x + y RV FP 8 FP 12 Wht s missing here? 11 prev Stck setup Need to set up on entry prev. push ebp mov ebp,e sub e, 4*l mov e, ebp 12 new new prev prev. prev. new prev. new l 2

3 Function f push ebp mov ebp,e function prologue sub e, 4*l f_epilogue mov e, ebp function epilogue The Glory of CISC f push ebp mov ebp,e sub e, 4*l f_epilogue mov e, ebp enter 4*l, 0 f_epilogue leve Clling conventions Hve described stndrd C clling convention rguments pushed on, in reverse order cller clens up rguments stdcll cllee clens up. MIPS/Alph first 4/6 rguments pssed in registers Choice of cller- vs. cllee-sve cller-sve cller must sve registers if needed fter cll; usble freely (e[cd]x) cllee-sve function not llowed to chnge; to use, must be sved (e[sd]i, e[sb]p, ebx) 15 Optimizing wy ebp No need for pointer register! Ide mintin constnt offset k between pointer nd pointer Use RISC-style rgument pssing rther thn pushing rguments on All references to (FP+n) trnslted to opernd [e+(n+k)] insted of to [ebp+n] Advntge get whole extr register to use when llocting registers (7!) 16 prev. prev. prev Stck setup sub e, 4*l dd e, 4*l + 4*l prev prev. 17 prev new mx rg ce new (size 4*l) Cvets Get even fster (nd RISC-core) prologue nd epilogue thn with enter/leve but To void breking cllers, must sve ebp register if we wnt to use it (cllee-sve) Doesn t work if is truly vrible-sized lloc(n) cll in C lloctes n bytes on the compiler cnnot predict not problem in Iot rrys -llocted, hs constnt size 18 3

4 Dynmic structures Modern progrmming lnguges llow dynmiclly llocted dt structures strings, rrys, objects C chr *x = (chr *)mlloc(strlen(s) + 1); C++ Foo *f = new Foo(); Jv Foo f = new Foo(); String s = s1 + s2; Iot x rry[int] = new int[5] (0); String s = s1 + s2; 19 Progrm Hep Progrm hs 4 memory res segment, segment,, Two typicl virtul memory lyouts (depends on OS) 20 Object lloction Dynmic objects llocted in the rry cretion, string conctention mlloc(n) urns new chunk of n bytes, free(x) releses memory strting t x Globls stticlly llocted in dt segment globl vribles string constnts ssembler supports dt segment declrtions 21 rry[t] Iot dynmic structures.length elements of new T [n] ( e ) = mlloc(4*n + 4); () = n; = + 4; 1 = ; 2 = + 4*n; while ( 1!= 2 ) ( ( 1 ) = -Ze[; 1 = ); PA4 We give you newrry, newstring clls with grbge collection support (no free cll needed) 22 Trivil register lloction Cn convert bstrct ssembly to rel ssembly esily (but generte bd ) Allocte every temporry to loction in the current rther thn to register Every temporry stored in different plce - - no possibility of conflict Three registers needed to shuttle dt in nd out of (mx. # registers used by one instruction) e.g, ex, ecx, edx 23 Rewriting bstrct Given instruction, replce every temporry in instruction with one of three registers e[cd]x Add mov instructions before instruction to lod registers properly Add mov instructions fter instruction to put dt bck onto (if necessry) push t1 mov ex, [ - t1off]; push ex mov [+4], t3? dd t1, [ - 4]? 24 4

5 Result Simple wy to get working Code is longer thn necessry, slower Also cn llocte temporries to registers until registers run out (3 temporries on Pentium, 20+ on MIPS, Alph) Code genertion technique ctully used by some compilers when ll optimiztion turned off (-O0) Will use for Progrmming Assignment 4 Summry Complete genertion technique Use tiling to perform instruction selection Arguments mpped to loctions, to temporries Function generted by gluing prologue, epilogue onto body Dynmic structure lloction hndled by relying on lloction routines (mlloc) Sttic structures llocted by dt segment ssembler declrtions Allocte temporries to loctions to eliminte use of unbounded # of registers Shuttle temporries in nd out using e[cd]x regs Where we re High-level source Assembly 27 5