Question

9.7.7 Benchfn.exe

Benchfn 是来自 Plum-Hall 基准程序套装的一个程序，测试函数调用；每轮循环完成 1000 个子程序调用。反汇编的程序在图 9-39 被显示，反编译的 C 程序在图 9-40，最初的 C 程序在图 9-41。这个程序有下列调用图：

main scanf printf proc_1 proc_2 proc_3 proc_4

Benchfn 有四个子过程和一个主程序。四个子过程其中三个调用其它子过程，而第四个子过程是空的。这个程序的中间指令数目的缩减比例没有前面几个程序那么高，因为在该程序中没有许多表达式 (通常在高级程序中不是这种情况)。从这个程序的统计可知 (见图 9-42)，空的子过程有 100%的缩减率，因为该子过程的序言和尾部低级指令在 C 程序中被清除；另外三个子过程对于它们执行的 29 个子过程调用平均有 29.30%的指令缩减率，而 main 程序有 81.08%的指令缩减率，因为在这个子过程中有使用表达式和赋值。该程序的总平均是比较低的，56.10%，这是因为这个程序较少有赋值语句。

	proc_4	PROC NEAR
000	0002FA	55	PUSH	bp
001	0002FB	8BEC	MOV	bp,sp
002	0002FD	5D	POP	bp
003	0002FE	C3	RET
	proc_4	ENDP
	proc_3	PROC NEAR
000	0002FF	55	PUSH	bp
001	000300	8BEC	MOV	bp,sp
002	000302	E8F5FF	CALL	near ptr proc_4
003	000305	E8F2FF	CALL	near ptr proc_4
004	000308	E8EFFF	CALL	near ptr proc_4
005	00030B	E8ECFF	CALL	near ptr proc_4
006	00030E	E8E9FF	CALL	near ptr proc_4
007	000311	E8E6FF	CALL	near ptr proc_4
008	000314	E8E3FF	CALL	near ptr proc_4
009	000317	E8E0FF	CALL	near ptr proc_4
010	00031A	E8DDFF	CALL	near ptr proc_4
011	00031D	E8DAFF	CALL	near ptr proc_4
012	000320	5D	POP	bp
013	000321	C3	RET
	proc_3	ENDP
	proc_2	PROC NEAR
000	000322	55	PUSH	bp
001	000323	8BEC	MOV	bp,sp
002	000325	E8D7FF	CALL	near ptr proc_3
003	000328	E8D4FF	CALL	near ptr proc_3
004	00032B	E8D1FF	CALL	near ptr proc_3
005	00032E	E8CEFF	CALL	near ptr proc_3
006	000331	E8CBFF	CALL	near ptr proc_3
007	000334	E8C8FF	CALL	near ptr proc_3
008	000337	E8C5FF	CALL	near ptr proc_3
009	00033A	E8C2FF	CALL	near ptr proc_3
010	00033D	E8BFFF	CALL	near ptr proc_3
011	000340	E8BCFF	CALL	near ptr proc_3
012	000343	5D	POP	bp
013	000344	C3	RET
	proc_2	ENDP
	proc_1	PROC NEAR
000	000345	55	PUSH	bp
001	000346	8BEC	MOV	bp,sp
002	000348	E8D7FF	CALL	near ptr proc_2
003	00034B	E8D4FF	CALL	near ptr proc_2
004	00034E	E8D1FF	CALL	near ptr proc_2
005	000351	E8CEFF	CALL	near ptr proc_2
006	000354	E8CBFF	CALL	near ptr proc_2
007	000357	E8C8FF	CALL	near ptr proc_2
008	00035A	E8C5FF	CALL	near ptr proc_2
009	00035D	E8C2FF	CALL	near ptr proc_2
010	000360	E8BFFF	CALL	near ptr proc_2
011	000363	5D	POP	bp
012	000364	C3	RET
	proc_1	ENDP
	main	PROC NEAR
000	000365	55	PUSH	bp
001	000366	8BEC	MOV	bp,sp
002	000368	83EC08	SUB	sp,8
003	00036B	8D46FC	LEA	ax,[bp-4]
004	00036E	50	PUSH	ax
005	00036F	B89401	MOV	ax,194h
006	000372	50	PUSH	ax
007	000373	E85614	CALL	near ptr scanf
008	000376	59	POP	cx
009	000377	59	POP	cx
010	000378	FF76FE	PUSH	word ptr [bp-2]
011	00037B	FF76FC	PUSH	word ptr [bp-4]
012	00037E	B89801	MOV	ax,198h
013	000381	50	PUSH	ax
014	000382	E8BE0B	CALL	near ptr printf
015	000385	83C406	ADD	sp,6
016	000388	C746FA0000	MOV	word ptr [bp-6],0
017	00038D	C746F80100	MOV	word ptr [bp-8],1
019	00039F	8B56FA	L1: MOV	dx,[bp-6]
020	0003A2	8B46F8	MOV	ax,[bp-8]
021	0003A5	3B56FE	CMP	dx,[bp-2]
022	0003A8	7CEA	JL	L2
023	0003AA	7F05	JG	L3
024	0003AC	3B46FC	CMP	ax,[bp-4]
025	0003AF	76E3	JBE	L2
026	0003B1	B8B201	L3: MOV	ax,1B2h
027	0003B4	50	PUSH	ax
028	0003B5	E88B0B	CALL	near ptr printf
029	0003B8	59	POP	cx
030	0003B9	8BE5	MOV	sp,bp
031	0003BB	5D	POP	bp
032	0003BC	C3	RET
033	000394	E8AEFF	L2: CALL	near ptr proc_1
034	000397	8346F801	ADD	word ptr [bp-8],1
035	00039B	8356FA00	ADC	word ptr [bp-6],0
036			JMP	L1	;Synthetic inst
	main	ENDP

图 9-39: Benchfn.a2

/* * Input file : benchfn.exe * File type : EXE */ #include "dcc.h" void proc_4 () /* Takes no parameters. * High-level language prologue code. */ { } void proc_3 () /* Takes no parameters. * High-level language prologue code. */ { proc_4 (); proc_4 (); proc_4 (); proc_4 (); proc_4 (); proc_4 (); proc_4 (); proc_4 (); proc_4 (); proc_4 (); } void proc_2 () /* Takes no parameters. * High-level language prologue code. */ { proc_3 (); proc_3 (); proc_3 (); proc_3 (); proc_3 (); proc_3 (); proc_3 (); proc_3 (); proc_3 (); proc_3 (); } void proc_1 () /* Takes no parameters. * High-level language prologue code. */ { proc_2 (); proc_2 (); proc_2 (); proc_2 (); proc_2 (); proc_2 (); proc_2 (); proc_2 (); proc_2 (); } void main () /* Takes no parameters. * High-level language prologue code. */ { long loc1; long loc2; scanf ("%ld", &loc2); printf ("executing %ld iterations\n", loc2); loc1 = 1; while ((loc1 <= loc2)) { proc_1 (); loc1 = (loc1 + 1); } printf ("finished\n"); }

图 9-40: Benchfn.b

/* benchfn - benchmark for function calls * Thomas Plum, Plum Hall Inc, 609-927-3770 * Let T be the execution time in milliseconds * Then average time per operator = T/major usec * (Because the inner loop has exactly 1000 operations) */ #include <stdio.h> f3() { ;} f2() { f3();f3();f3();f3();f3();f3();f3();f3();f3();f3();} /* 10 */ f1() { f2();f2();f2();f2();f2();f2();f2();f2();f2();f2();} /* 10 */ f0() { f1();f1();f1();f1();f1();f1();f1();f1();f1();} /* 9 */ main (int ac, char *av[]) { long d, major; scanf ("%ld", &major); printf("executing %ld iterations\n", major); for (d = 1; d <= major; ++d) f0(); /* executes 1000 calls */ printf ("finished\n"); }

图 9-41: Benchfn.c

子程序	低级	高级	% 缩减率
proc4	4	0	100.00
proc3	14	10	28.57
proc2	14	10	28.57
proc1	13	9	30.77
main	37	7	81.08
合计	82	36	56.10

图 9-42: Benchfn 统计