Another Optimization Problem

If you are referring to _my_ program, yes, it works when the main() isn't removed (i.e. when I compile with the debug flag set, or one of the other optimization options).

It _doesn't_ work when it jumps to the main and executes a whole bunch of nops.

Is that what you were asking?
JG.

"Is that what you were asking?"

Yes. If your program worked I'd have said the optimisation was normal. As it doesn't, I'd say the optimisation *may* not be normal.

Can you try and reduce your program to the minimum that doesn't work at this particular optimisation level then post the .cod file?

Have you tried levels 9, 10 or 11 alternately speed and size optimisation to see what happens?

What version of compiler and linker are you using?

Stefan

Hi there,

I'm trying to generate a small test case as per Stefan's suggestion, but the problem seems to be code-related (i.e. if the size of the main() function changes, so does the behaviour).

Changing optimization levels makes the problem seem to go away in this case. Level 8 is the only one that manifests this problem and changing the speed/size emphasis has no effect.

The versions are:
C51.exe V7.00
A51.exe V7.00a
BL51.exe V5.00
LIB51.exe V4.23
OH51.exe V2.6

I loaded the application into the debugger and checked the disassembly and it looks like the main() is zeroed out, so I guess this means the object file already is missing the main().

There are no compiler errors or warnings, but during linking, I get 9 "L16: Uncalled Segment, Ignored for Overlay Process" warnings.

Thanks again for all your help.
V.

I get 9 "L16: Uncalled Segment, Ignored for Overlay Process" warnings.

What segments are uncalled?

Jon

Ok, I think I have some code that will exhibit the problem I'm having. I've tried several combinations of optimizations with and without debug info and the results seem to vary considerably depending on the code. With some code, the main function is deleted with many different settings while with other code, it only gets deleted with a very specific setting. In any case, it would be nice to determine the exact cause.

The following is the simplest code that I could compile that shows the problem I'm having:

sfr COM0 = 0xBC;

void DummyCall()
{
}

void main()
{
unsigned char Temp_A;
unsigned char Temp_B;

	Temp_A = 0;
	Temp_B = 1;

	COM0 = 0x55;

	while(1);

	while (1)
	{
		while(1);
		if (1)
		{
			do
			{
				DummyCall();
			} while (Temp_A != Temp_B);
		}
	}
}

I compiled your example. Here are my results.

1. I ALWAYS receive the following linker warning:

*** WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
    SEGMENT: ?PR?DUMMYCALL?MAIN

C:0x0000    020003   LJMP     C:0003
C:0x0003    787F     MOV      R0,#0x7F
C:0x0005    E4       CLR      A
C:0x0006    F6       MOV      @R0,A
C:0x0007    D8FD     DJNZ     R0,C:0006
C:0x0009    758107   MOV      SP(0x81),#0x07
C:0x000C    02000F   LJMP     main(C:000F)
     7: void main()
     8: {
     9: unsigned char Temp_A;
    10: unsigned char Temp_B;
    11:
    12:         Temp_A = 0;
C:0x000F    E4       CLR      A
C:0x0010    FF       MOV      R7,A
    13:         Temp_B = 1;
    14:
C:0x0011    7E01     MOV      R6,#0x01
    15:         COM0 = 0x55;
    16:
C:0x0013    75BC55   MOV      COM0(0xBC),#0x55
    17:         while(1);
C:0x0016    80FE     SJMP     C:0016
     3: void DummyCall()
C:0x0018    22       RET

C:0x0000    020003   LJMP     C:0003
C:0x0003    787F     MOV      R0,#0x7F
C:0x0005    E4       CLR      A
C:0x0006    F6       MOV      @R0,A
C:0x0007    D8FD     DJNZ     R0,C:0006
C:0x0009    758107   MOV      SP(0x81),#0x07
C:0x000C    02000F   LJMP     C:000F
C:0x000F    E4       CLR      A
C:0x0010    FF       MOV      R7,A
C:0x0011    7E01     MOV      R6,#0x01
C:0x0013    75BC55   MOV      0xBC,#0x55
C:0x0016    80FE     SJMP     C:0016
C:0x0018    22       RET      

• Make sure that we're build the project the same way.

• Test the HEX files generated from the debug version and the non-debug version to see if they are the same.

• How are you debugging? Are you using the Keil debugger or another debugger? If using another debugger, how old (or new) is it? Has it incorporated all the latest changes to the OMF51 specification?

Thanks Jon,

I was using the Keil debugger to get the disassembly. I've tested the hex file on my system (using the COM0 sfr) and I've examined the Hex file by hand as well. I don't see anything strange.

When I build, the _only_ thing I changed was the debug info flag.

Perhaps you _do_ have newer versions of the tools. I'm using OH51 V2.6.

Hi Jon,

I just downloaded the newest tools from Keil and updated everything.

Seems like the problem is gone and I get the same results as you.

Thanks a lot for all your help. I just hope the problem is _really_ fixed this time. It just seems a bit scary that things were so intermittent.

I just downloaded the newest tools from Keil and updated everything.

Oops. I guess we should have checked the version number from the beginning.

Jon

Yes, Stefan _did_ ask which versions I was using.

I looked through the update notes, but didn't find anything specifically related to this problem.

Might have another surprise waiting for us in a few months :)

"I looked through the update notes, but didn't find anything specifically related to this problem."

Indeed, perhaps Jon can show us where this bug is documented?

Stefan