Revision as of 10:55, 16 February 2017 (view source) Root (talk | contribs) (→‎Compiling and Running) ← Older edit		Revision as of 08:18, 9 May 2017 (view source) Root (talk | contribs) (→‎Function "mkvec") Newer edit →
Line 59:		Line 59:
	LABEL mkvec		LABEL mkvec
	ENTER 8  ; s@-4 v@-8		ENTER 8  ; s@-4 v@-8
−	LOCV 8	+	LOCAL 8
		+	LOAD
	INT 1		INT 1
	LT		LT
Line 76:		Line 77:
	LABEL ifend1		LABEL ifend1
	INT 8  ; sizeof(double)		INT 8  ; sizeof(double)
−	LOCA -4	+	LOCAL -4
−	LOCV +8	+	STORE
−	LOCV -4	+	LOCAL +8
		+	LOAD
		+	LOCAL -4
		+	LOAD
	MUL		MUL
	CALL malloc		CALL malloc
Line 86:		Line 90:
	TRASH 4		TRASH 4
	PUSH		PUSH
−	LOCA -8	+	LOCAL -8
−	LOCV -8	+	STORE
		+	LOCAL -8
		+	LOAD
	POP		POP
	LEAVE		LEAVE

---

Revision as of 08:18, 9 May 2017

Contents 1 The Original Code 2 Postfix Code 2.1 Variables 2.2 Declaration of external function 2.3 Function "mkvec" 2.4 Function "compute" 3 Compiling and Running

The Original Code

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.

<c> static unsigned long a = 10; static double *v; extern void *malloc(unsigned long);

static double *mkvec(unsigned long n) {

 if (n < 1) return (double *)0;
 unsigned long s = sizeof(double);
 double *v = (double *)malloc(n * s);
 return v;

}

double *compute() {

 v = mkvec(a * 4);
 for (unsigned long i = 1; i < a; i++)
   if (v[i] > v[0]) v[i] = 3 * i - 1;
 return v;

} </c>

Postfix Code

The Postfix code for the above code is as follows: (code has not been thoroughly checked: bug reports are welcome)

In the following code sections, BB# means "basic block number".

Variables

<asm>

variable "a"

DATA ALIGN LABEL a CONST 10

variable "v"

DATA  ; "static" variables are always initialized ALIGN LABEL v CONST 0  ; this is a null pointer </asm>

Declaration of external function

<asm> EXTERN malloc </asm>

Function "mkvec"

<asm>

start of BB1

TEXT ALIGN LABEL mkvec ENTER 8  ; s@-4 v@-8 LOCAL 8 LOAD INT 1 LT JZ ifend1

end of BB1

start of BB2

INT 0 POP LEAVE RET

end of BB2

start of BB3

ALIGN LABEL ifend1 INT 8  ; sizeof(double) LOCAL -4 STORE LOCAL +8 LOAD LOCAL -4 LOAD MUL CALL malloc

end of BB3

start of BB4

TRASH 4 PUSH LOCAL -8 STORE LOCAL -8 LOAD POP LEAVE RET

end of BB4

</asm>

Function "compute"

<asm>

start of BB1

TEXT ALIGN GLOBAL compute, FUNC LABEL compute ENTER 4  ; i@-4 ADDRV a INT 4 MUL CALL mkvec

end of BB1

start of BB2

TRASH 4 PUSH DUP ADDRA v TRASH 4 INT 1 LOCA -4

end of BB2

start of BB3

ALIGN LABEL fortest LOCV -4 ADDRV a LT JZ forend

end of BB3

start of BB4

ADDRV v LOCV -4 INT 8 MUL ADD DLOAD ADDRV v INT 0 INT 8 MUL ADD DLOAD DCMP INT 0 GT JZ ifend2

end of BB4

start of BB5

INT 3 LOCV -4 MUL INT 1 SUB I2D DDUP ADDRV v LOCV -4 INT 8 MUL ADD DSTORE TRASH 8

end of BB5

start of BB6

ALIGN LABEL ifend2 ALIGN LABEL forincr LOCV -4 DUP INT 1 ADD LOCA -4 TRASH 4 JMP fortest

end of BB6

start of BB7

ALIGN LABEL forend ADDRV v POP LEAVE RET

end of BB7

</asm>

Compiling and Running

To compile the Postfix code directly, pf2asm can be used (assuming a 32-bit architecture):

pf2asm compute.pf
yasm -felf compute.asm