Hello,
1.when i use printf with no var_args then the compiler should call puts instead of printf.
ex1:
#include <REGX51.H> #include <stdio.h> void main(void) { printf("This must call puts instead of printf"); }
Program Size: data=30.1 xdata=0 code=1103
ex2:
#include <REGX51.H> #include <stdio.h> void main(void) { puts("This must call puts instead of printf"); }
Program Size: data=9.0 xdata=0 code=168
The above code links the printf function from the library which is huge(produces 1103 bytes).But the compiler can use puts when there is no var_args given which is much smaller than printf(produces 168 bytes).
2.The Compiler must find and remove the duplicate constant strings
ex3:
#include <REGX51.H> #include <stdio.h> void main(void) { puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); puts("This string gets duplicated as many time as i use it"); }
Program Size: data=9.0 xdata=0 code=334
ex4:
#include <REGX51.H> #include <stdio.h> void main(void) { puts("This string gets duplicated as many time as i use it"); }
Program Size: data=9.0 xdata=0 code=183
3.Bit Test instructions are not used when i actually test for the bit
ex5:
#include <REGX51.H> #include <stdio.h> void main(void) { if(P0^1) { P1 = 10; } } ASSEMBLY LISTING OF GENERATED OBJECT CODE ; FUNCTION main (BEGIN) ; SOURCE LINE # 6 ; SOURCE LINE # 7 ; SOURCE LINE # 8 0000 E580 MOV A,P0 0002 6401 XRL A,#01H 0004 6003 JZ ?C0002 ; SOURCE LINE # 9 ; SOURCE LINE # 10 0006 75900A MOV P1,#0AH ; SOURCE LINE # 11 ; SOURCE LINE # 13 0009 ?C0002: 0009 22 RET ; FUNCTION main (END)
In the above assembly output it should have used a single instruction JNB instead of three MOV,XRL and JZ.This is very basic anybody would object the assembly code produced.
I have not used the compiler much.But the compiler needs a look by the programmers at keil.
The above programs were all compiled with compiler optimisation level set to 9 & favour speed.
About 5 years back i compiled a c51 source code using keil. Now i recompiled the same source code with the latest compiler from keil and compared the two output .hex files. Unfortunately it produced exactly the same output.Here i was expecting some code and data size reduction as the compiler must be capable of optimising more.
It seems there was no improvement on the compiler side.
It is not a complaint but in the interest of improving the compiler.
regards,
S.Sheik mohamed
But the compiler needs a look by the programmers at keil
No dear Sheik: you need to know what you're doing and what you're talking about, before making baseless accusations!
The Above produces the following assembly code
ASSEMBLY LISTING OF GENERATED OBJECT CODE ; FUNCTION main (BEGIN) ; SOURCE LINE # 4 ; SOURCE LINE # 5 ; SOURCE LINE # 6 0000 7BFF MOV R3,#0FFH 0002 7A00 R MOV R2,#HIGH ?SC_0 0004 7900 R MOV R1,#LOW ?SC_0 ; SOURCE LINE # 7 ; SOURCE LINE # 8 ; SOURCE LINE # 9 ; SOURCE LINE # 10 ; SOURCE LINE # 11 ; SOURCE LINE # 12 ; SOURCE LINE # 13 ; SOURCE LINE # 14 ; SOURCE LINE # 15 ; SOURCE LINE # 16 ; SOURCE LINE # 17 ; SOURCE LINE # 18 ; SOURCE LINE # 19 ; SOURCE LINE # 20 ; SOURCE LINE # 21 ; SOURCE LINE # 22 0006 120000 R LCALL L?0002 ; SOURCE LINE # 23 ; SOURCE LINE # 24 ; SOURCE LINE # 25 ; SOURCE LINE # 26 ; SOURCE LINE # 27 ; SOURCE LINE # 28 ; SOURCE LINE # 29 ; SOURCE LINE # 30 ; SOURCE LINE # 31 ; SOURCE LINE # 32 ; SOURCE LINE # 33 ; SOURCE LINE # 34 ; SOURCE LINE # 35 ; SOURCE LINE # 36 ; SOURCE LINE # 37 ; SOURCE LINE # 38 0009 120000 R LCALL L?0002 000C 020000 E LJMP _puts ; SOURCE LINE # 39 000F L?0002: 000F 120000 E LCALL _puts 0012 7BFF MOV R3,#0FFH 0014 7A00 R MOV R2,#HIGH ?SC_0 0016 7900 R MOV R1,#LOW ?SC_0 0018 120000 E LCALL _puts 001B 7BFF MOV R3,#0FFH 001D 7A00 R MOV R2,#HIGH ?SC_0 001F 7900 R MOV R1,#LOW ?SC_0 0021 120000 E LCALL _puts 0024 7BFF MOV R3,#0FFH 0026 7A00 R MOV R2,#HIGH ?SC_0 0028 7900 R MOV R1,#LOW ?SC_0 002A 120000 E LCALL _puts 002D 7BFF MOV R3,#0FFH 002F 7A00 R MOV R2,#HIGH ?SC_0 C51 COMPILER V9.02 T 12/12/2010 06:18:02 PAGE 3 0031 7900 R MOV R1,#LOW ?SC_0 0033 120000 E LCALL _puts 0036 7BFF MOV R3,#0FFH 0038 7A00 R MOV R2,#HIGH ?SC_0 003A 7900 R MOV R1,#LOW ?SC_0 003C 120000 E LCALL _puts 003F 7BFF MOV R3,#0FFH 0041 7A00 R MOV R2,#HIGH ?SC_0 0043 7900 R MOV R1,#LOW ?SC_0 0045 120000 E LCALL _puts 0048 7BFF MOV R3,#0FFH 004A 7A00 R MOV R2,#HIGH ?SC_0 004C 7900 R MOV R1,#LOW ?SC_0 004E 120000 E LCALL _puts 0051 7BFF MOV R3,#0FFH 0053 7A00 R MOV R2,#HIGH ?SC_0 0055 7900 R MOV R1,#LOW ?SC_0 0057 120000 E LCALL _puts 005A 7BFF MOV R3,#0FFH 005C 7A00 R MOV R2,#HIGH ?SC_0 005E 7900 R MOV R1,#LOW ?SC_0 0060 120000 E LCALL _puts 0063 7BFF MOV R3,#0FFH 0065 7A00 R MOV R2,#HIGH ?SC_0 0067 7900 R MOV R1,#LOW ?SC_0 0069 120000 E LCALL _puts 006C 7BFF MOV R3,#0FFH 006E 7A00 R MOV R2,#HIGH ?SC_0 0070 7900 R MOV R1,#LOW ?SC_0 0072 120000 E LCALL _puts 0075 7BFF MOV R3,#0FFH 0077 7A00 R MOV R2,#HIGH ?SC_0 0079 7900 R MOV R1,#LOW ?SC_0 007B 120000 E LCALL _puts 007E 7BFF MOV R3,#0FFH 0080 7A00 R MOV R2,#HIGH ?SC_0 0082 7900 R MOV R1,#LOW ?SC_0 0084 120000 E LCALL _puts 0087 7BFF MOV R3,#0FFH 0089 7A00 R MOV R2,#HIGH ?SC_0 008B 7900 R MOV R1,#LOW ?SC_0 008D 120000 E LCALL _puts 0090 7BFF MOV R3,#0FFH 0092 7A00 R MOV R2,#HIGH ?SC_0 0094 7900 R MOV R1,#LOW ?SC_0 0096 120000 E LCALL _puts 0099 7BFF MOV R3,#0FFH 009B 7A00 R MOV R2,#HIGH ?SC_0 009D 7900 R MOV R1,#LOW ?SC_0 009F 22 RET ; FUNCTION main (END)
The optimiser should have used a counter and repeated the following block
MOV R3,#0FFH MOV R2,#HIGH ?SC_0 MOV R1,#LOW ?SC_0 LCALL _puts
I am not accusing,complaining or under estimating any one either at keil or in this forum I think only when we discuss we can improve.
If by anyway i hurted anybody's heart please forgive me!!
No, it does not - because the code that you have written does not test for a bit!
As already explained to you, the code you have written contains an expression using the ANSI Standard exclusive-OR operator.
Perhaps you are confusing the meaning of "bitwise", as used by the ANSI Standard, with the individual bit operations of the 8051...?
1) printf() does not do the same thing as puts() even if you send a constant not containing any % parameter expansions. Haven't you stil read up on puts() and seen what it does, _besides_ emitting the text string?
Well? I'm waiting. Have you read the documentation for puts yet? Still waiting...
2) You want the fastest code? Converting a sequence of calls put puts() with a loop isn't faster. Many optimizing compilers actually does the reverse. They do loop unrolling where they intentionally duplicate the code inside the loop to reduce the number of loop iterations - sometimes totally unrolling the loop so no loop operation remains.
3) my_byte XOR 1 inverts one bit in a byte, and then tests if the byte result is non-zero. That is not a single-bit operation that may use any bit instructins in the 8051 processor. The ^ may _only_ be used when declaring bit variables, since it is an overload of a standard C operator for XOR. And the standard C operator performs bit operations on full bytes/shorts/ints/long ints and not on a single bit.
Somehow, you have to switch from output mode into input mode. You must pick up the feedback you get in the forum, and not just run along further and further away on the wrong track.
www.cplusplus.com/.../ www.cplusplus.com/.../
Spot the difference!
Ok,
In that case atleast the compiler could even have different versions of printf and use the one which is appropriate for the current project.
That is if i have never used float inside printf in my project then float to string part of the printf library is not neccessary.
The comipler/linker during optimization can decide which printf library would be suitable for my project.
"That is if i have never used float inside printf in my project then float to string part of the printf library is not neccessary"
That is exactly what happens already!
Have you now understood why the code that you thought did a single-bit test does not actually do a single-bit test?
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