[sdcc-devel] [ sdcc-Bugs-648857 ] "dead-optimizing" while-loop

[<no...@so...>]

Bugs item #648857, was opened at 2002-12-05 09:28
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=100599&aid=648857&group_id=599

Category: msc51(8051) target
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Carsten Pahl (cpschnuffel)
Assigned to: Nobody/Anonymous (nobody)
Summary: "dead-optimizing" while-loop

Initial Comment:
Hi there,
I have a (little) problem with the optimizing routines
of sdcc 2.3.2. A self-written module for the internal
UART of an 8051 contains the interrupt service routine,
in which I set a module-globale variable if  a byte is
sended successfully. This variable is a loop condition
for the sending routine to wait until the byte is
sended. If I compile the module, sdcc says
"warning: conditional flow changed by optimizer: so
said EVELYN the modified dog" and points to the while
loop. Additionally, it gives me two "unreachable code"
warnings for code lines after the while loop. Here's a
code snippet:

...
// This is the flag set by the isr and read by the send
routine
static unsigned char g_ucTransmitFlag = 0;
...

void vUART_ISR(void) interrupt 4
{ 
...	
  if (TI)
  {
    // Here the flag is set	
    g_ucTransmitFlag = 1;
	
    // Delete TI
    TI = 0;	
  }
...
}

...

// This is the sending routine
void vUART_Send(void)
{
  unsigned char ucCounter;
  ...	

  // send whole buffer
  ucCounter = 0;  
  do
  {
    // send next byte
    SBUF = g_ucSendBuffer[ucCounter];
		
    // wait until byte transfered
    while(!g_ucTransmitFlag);
    g_ucTransmitFlag = 0;
		
    // increment counter
    ucCounter++;
  }
  while(ucCounter < g_ucSendSize);
  ...

}

I hope somebody can help me to solve the problem
without deactivating the whole loop optimization.

Best regards

Carsten


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