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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
In strict ANSI 'C', the integral constant is considered an int, and the 8-bit value would be promoted to an int before doing a bitwise 'AND' of all bits and giving an int result.
With the integer promotion, the semantics of the operation do not change: the code is still testing for a bit. In this particular case, if the compiler knew that the register is bit-addressable and chose not to ignore this information it could test for this bit directly.
But the only way to get Keil C51 to operate on a single bit is to use the specific bit operations.
Well, that's the point. A smarter compiler will use faster and more compact code constructs where appropriate. This is clearly one of those cases.
Again, ANSI 'C' bitwise operators have noting to do with the 8051's single-bit operations!
I'm not sure what you mean by that. I've seen the Green Hills compiler for Coldfire generate BSET and BCLR instructions when I was using bitwise OR and bitwise AND operators to set or clear bits. Why wouldn't C51 do the same? Especially since the 8051 core does a read-modify-write internally to set or clear bits, so semantics are the same.
"I've seen the Green Hills compiler for Coldfire generate BSET and BCLR instructions when I was using bitwise OR and bitwise AND operators to set or clear bits. Why wouldn't C51 do the same?"
Was that with SFR or volatile variables? Or was it with normal variables?
It really is important to separate SFR and volatile variables from standard char/int/... variables when discussing single-bit accesses.