Revision as of 08:18, 9 May 2017 (view source) Root (talk | contribs) (→‎Function "mkvec") ← Older edit		Revision as of 08:20, 9 May 2017 (view source) Root (talk | contribs) (→‎Function "compute") Newer edit →
Line 109:		Line 109:
	LABEL compute		LABEL compute
	ENTER 4  ; i@-4		ENTER 4  ; i@-4
−	ADDRV a	+	ADDR a
		+	LOAD
	INT 4		INT 4
	MUL		MUL
Line 119:		Line 120:
	PUSH		PUSH
	DUP		DUP
−	ADDRA v	+	ADDR v
		+	STORE
	TRASH 4		TRASH 4
	INT 1		INT 1
−	LOCA -4	+	LOCAL -4
		+	STORE
	;; end of BB2		;; end of BB2
Line 128:		Line 131:
	ALIGN		ALIGN
	LABEL fortest		LABEL fortest
−	LOCV -4	+	LOCAL -4
−	ADDRV a	+	LOAD
		+	ADDR a
		+	LOAD
	LT		LT
	JZ forend		JZ forend
Line 135:		Line 140:
	;; start of BB4		;; start of BB4
−	ADDRV v	+	ADDR v
−	LOCV -4	+	LOAD
		+	LOCAL -4
		+	LOAD
	INT 8		INT 8
	MUL		MUL
	ADD		ADD
	DLOAD		DLOAD
−	ADDRV v	+	ADDR v
		+	LOAD
	INT 0		INT 0
	INT 8		INT 8
Line 155:		Line 163:
	;; start of BB5		;; start of BB5
	INT 3		INT 3
−	LOCV -4	+	LOCAL -4
		+	LOAD
	MUL		MUL
	INT 1		INT 1
Line 161:		Line 170:
	I2D		I2D
	DDUP		DDUP
−	ADDRV v	+	ADDR v
−	LOCV -4	+	LOAD
		+	LOCAL -4
		+	LOAD
	INT 8		INT 8
	MUL		MUL
Line 175:		Line 186:
	ALIGN		ALIGN
	LABEL forincr		LABEL forincr
−	LOCV -4	+	LOCAL -4
		+	LOAD
	DUP		DUP
	INT 1		INT 1
	ADD		ADD
−	LOCA -4	+	LOCAL -4
		+	STORE
	TRASH 4		TRASH 4
	JMP fortest		JMP fortest
Line 187:		Line 200:
	ALIGN		ALIGN
	LABEL forend		LABEL forend
−	ADDRV v	+	ADDR v
		+	LOAD
	POP		POP
	LEAVE		LEAVE

---

Revision as of 08:20, 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 ADDR a LOAD INT 4 MUL CALL mkvec

end of BB1

start of BB2

TRASH 4 PUSH DUP ADDR v STORE TRASH 4 INT 1 LOCAL -4 STORE

end of BB2

start of BB3

ALIGN LABEL fortest LOCAL -4 LOAD ADDR a LOAD LT JZ forend

end of BB3

start of BB4

ADDR v LOAD LOCAL -4 LOAD INT 8 MUL ADD DLOAD ADDR v LOAD INT 0 INT 8 MUL ADD DLOAD DCMP INT 0 GT JZ ifend2

end of BB4

start of BB5

INT 3 LOCAL -4 LOAD MUL INT 1 SUB I2D DDUP ADDR v LOAD LOCAL -4 LOAD INT 8 MUL ADD DSTORE TRASH 8

end of BB5

start of BB6

ALIGN LABEL ifend2 ALIGN LABEL forincr LOCAL -4 LOAD DUP INT 1 ADD LOCAL -4 STORE TRASH 4 JMP fortest

end of BB6

start of BB7

ALIGN LABEL forend ADDR v LOAD 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