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| {{TOCright}}
| | #REDIRECT [[ist:Code Generation/Exercise 9]] |
| == The Original Code ==
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| Consider the following C code and assume that the size of pointers, '''int''', and '''unsigned long''' is 32 bits and that the size of '''double''' is 64 bits.
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| <c>
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| static unsigned long a = 10;
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| static double *v;
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| extern void *malloc(unsigned long);
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| static double *mkvec(unsigned long n) {
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| if (n < 1) return (double *)0;
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| unsigned long s = sizeof(double);
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| double *v = (double *)malloc(n * s);
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| return v;
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| }
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| double *compute() {
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| v = mkvec(a * 4);
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| for (unsigned long i = 1; i < a; i++)
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| if (v[i] > v[0]) v[i] = 3 * i - 1;
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| return v;
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| }
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| </c>
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| == Postfix Code ==
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| The Postfix code for the above code is as follows: (code has not been thoroughly checked: bug reports are welcome)
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| In the following code sections, '''BB#''' means "[[Optimization Topics|basic block]] number".
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| === Variables ===
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| <asm>
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| ;; variable "a"
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| DATA
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| ALIGN
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| LABEL a
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| CONST 10
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| ;; variable "v"
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| DATA ; "static" variables are always initialized
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| ALIGN
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| LABEL v
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| CONST 0 ; this is a null pointer
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| </asm>
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| === Declaration of external function ===
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| <asm>
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| EXTERN malloc
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| </asm>
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| === Function "mkvec" ===
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| <asm>
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| ;; start of BB1
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| TEXT
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| ALIGN
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| LABEL mkvec
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| ENTER 8 ; s@-4 v@-8
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| LOCV 8
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| INT 1
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| LT
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| JZ ifend1
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| ;; end of BB1
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| ;; start of BB2
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| INT 0
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| POP
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| LEAVE
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| RET
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| ;; end of BB2
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| ;; start of BB3
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| ALIGN
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| LABEL ifend1
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| INT 8 ; sizeof(double)
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| LOCA -4
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| LOCV +8
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| LOCV -4
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| MUL
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| CALL malloc
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| ;; end of BB3
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| ;; start of BB4
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| TRASH 4
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| PUSH
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| LOCA -8
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| LOCV -8
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| POP
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| LEAVE
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| RET
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| ;; end of BB4
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| </asm>
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| === Function "compute" ===
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| <asm>
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| ;; start of BB1
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| TEXT
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| ALIGN
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| GLOBAL compute, FUNC
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| LABEL compute
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| ENTER 4 ; i@-4
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| ADDRV a
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| INT 4
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| MUL
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| CALL mkvec
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| ;; end of BB1
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| ;; start of BB2
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| TRASH 4
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| PUSH
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| DUP
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| ADDRA v
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| TRASH 4
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| INT 1
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| LOCA -4
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| ;; end of BB2
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| ;; start of BB3
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| ALIGN
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| LABEL fortest
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| LOCV -4
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| ADDRV a
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| LT
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| JZ forend
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| ;; end of BB3
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| ;; start of BB4
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| ADDRV v
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| LOCV -4
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| INT 8
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| MUL
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| ADD
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| DLOAD
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| ADDRV v
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| INT 0
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| INT 8
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| MUL
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| ADD
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| DLOAD
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| DCMP
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| INT 0
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| GT
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| JZ ifend2
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| ;; end of BB4
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| ;; start of BB5
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| INT 3
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| LOCV -4
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| MUL
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| INT 1
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| SUB
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| I2D
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| DDUP
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| ADDRV v
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| LOCV -4
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| INT 8
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| MUL
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| ADD
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| DSTORE
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| TRASH 8
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| ;; end of BB5
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| ;; start of BB6
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| ALIGN
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| LABEL ifend2
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| ALIGN
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| LABEL forincr
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| LOCV -4
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| DUP
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| INT 1
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| ADD
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| LOCA -4
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| TRASH 4
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| JMP fortest
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| ;; end of BB6
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| ;; start of BB7
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| ALIGN
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| LABEL forend
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| ADDRV v
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| POP
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| LEAVE
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| RET
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| ;; end of BB7
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| </asm>
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| == Compiling and Running ==
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| To compile the Postfix code directly, [[pf2asm]] can be used (assuming a 32-bit architecture):
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| * pf2asm compute.pf
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| * yasm -felf compute.asm
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| [[category:Compilers]]
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| [[category:Teaching]]
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