Compiler Error or User Error?

[Paolomio]

The following code, in xc:

Code: Select all

#pragma loop unroll
void test(void)
{
	int j, x;
	while(1)
	{
		for(j = 5; j >= 1; j--)
		{
			x = j+1;
		}
	}
}

causes the following error from the compiler:

xcc1: terminated due to internal unrecoverable error

If I comment out the while(1) loop it compiles fine. Any ideas what's wrong?

Paul

[segher]

That's a compiler bug (it tells you it is).

Maybe it tries to unroll the infinite loop, like you asked it to :-)

[Paolomio]

It may be a compiler bug, but to be clear my code is not asking it to unroll an infinitely long loop. It's asking it to unroll a finite loop and run it for an infinitely long time. There is some difference there.

Paul

[Folknology]

What happens if you move the pragma to the line above the For loop but below the while, does that make any difference?

regards
Al

[Paolomio]

What happens if you move the pragma to the line above the For loop but below the while, does that make any difference?

The pragma is function-wide, and must appear above the affected function.

No luck there...

[Folknology]

What about something ugly like:

Code: Select all

#pragma loop unroll
void test(void)
{
   int j, x;
   asm("\n.loop:\n")
      for(j = 5; j >= 1; j--)
      {
         x = j+1;
      }
   asm("\n bu .loop \n");
}

[Paolomio]

What about something ugly like:

I don't know, but the real problem is that this looks like a compiler bug. I'll submit a ticket to see what XMOS says...

[Bianco]

What happens if you move the pragma to the line above the For loop but below the while, does that make any difference?

The pragma is function-wide, and must appear above the affected function.

No luck there...

Says who?

#pragma loop unroll (n) (XC only)

This pragma controls the number of times the next do, while or for loop in the
current function is unrolled. n specifies the number of iterations to unroll, and
unrolling is performed only at optimization level 01 and higher. Omitting the
(n ) parameter causes the compiler to try and fully unroll the loop. Outside of a
function the pragma is ignored. The compiler produces a warning if unable to
perform the unrolling.

Code: Select all

void test(streaming chanend c)
{
   int j, x;
   while(1)
   {
      #pragma loop unroll
      for(j = 5; j >= 1; j--)
      {
         x = j+1;
         c <: x;
      }
   }
}

works fine here.
I added a chanend to avoid the while loop being optimized to nothing because nothing useful is done with x.

Code: Select all

test:
.L26:
.L12:
.L16:
.L17:
          ldc       r1, 0x6
.L64:
          out       res[r0], r1 
.L19:
          ldc       r1, 0x5
.L65:
          out       res[r0], r1 
          ldc       r1, 0x4
.L66:
          out       res[r0], r1 
          mkmsk     r1, 0x2
.L67:
          out       res[r0], r1 
          ldc       r1, 0x2
.L68:
          out       res[r0], r1 
          bu        .L12 

[Paolomio]

[

Outside of a
function the pragma is ignored.

Well, I totally missed that. What's strange is that it appeared to unroll a loop in a different function (generating sine samples at 3Ms/s with the pragma, and 500Ks/s without). Huh.