Is this a C compiler bug?

EricM

I've got some C code that looks like:

if( minuteCount > 0x3)
{
i = 0xAA; // debug
}

For some reason, it jumps into this code (setting i to 0xAA) even when minuteCount is set to 0. I set the view in Code Composer Studio to "Mixed Source/ASM" and I'm seeing:

if( minuteCount > 0x3)
00B72F 761F MOVW       DP,#0x02FA
00B731 9203 MOV        AL,@3
00B732 5203 CMPB       AL,#3
{
       i = 0xAA; // debug
00B733 56B2 MOVB       *-SP[3],#0x08,GT

}

I'm not an assembly expert, but shouldn't there be some kind of conditional jump made after the CMPB test of AL, when comparing it to #3?

I'm running Code Composer Studio 3.3.59.4

Code Generation Tools v5.0.0B2

Compiler settings:

-g -q -pdr -fr"$(Proj_dir)\Debug" -fs"$(Proj_dir)\Debug" -i"..\..\DSP2833x_headers\include" -i"..\..\DSP2833x_common\include" -i"C:\tidcs\c28\C28x_FPU_Lib\beta1\include" -d"_DEBUG" -d"LARGE_MODEL" -ml -mt -v28 --float_support=fpu32

Any ideas?

Thanks,

Eric

over 17 years ago

Raffaele over 17 years ago

Intellectual 545 points

Are you sure minuteCount is defined as int?

Then, to view complete asm code for your instructions, you should read more lines, because the assembly code you read is not in 1 to 1 sequentially correspondent to your C code. Try to read few lines forward and you'll see the branch instruction.

Regards,

Raffaele

EricM over 17 years ago in reply to Raffaele

Prodigy 140 points

Hi Raffaele,

Here's a simplified version that shows the compiler output:

int minuteCount = 0;
int i;

main()
{
if( minuteCount > 0x3)
{
000040      __text, .text, main:
000040 761F MOVW       DP,#0x0000
000042 9200 MOV        AL,@0
000043 5203 CMPB       AL,#3
  i = 0x55;
000044 56B2 MOVB       @1,#0x55,GT
}
000046 9A00 MOVB       AL,#0
}
000047 0006 LRETR

I still don't seem to see any conditional branching.

Thanks,

Eric

Mitja Nemec over 17 years ago in reply to EricM

Genius 5885 points

Hi Eric

The instuction at address 0x0044 MOVB @1,0x55,GT is a conditional move (move if GT (greater))

Hope this clears things up

Regards, Mitja

EricM over 17 years ago in reply to Mitja Nemec

Prodigy 140 points

Mitja,

Yes, that clears things up!

I apologize for my assembly language ignorance, I've been doing most of my development in "C".

Thanks,

Eric

Raffaele over 17 years ago in reply to Mitja Nemec

Intellectual 545 points

Oops, didn't see the GT... sorry :P

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Is this a C compiler bug?