🚀 go-pugleaf

In article <9532616.4242@mulga.cs.mu.OZ.AU>,
Fergus Henderson <fjh@munta.cs.mu.OZ.AU> wrote:
> But as you suggest below, on platforms for which stack allocation is
> difficult, the compiler could simply allocate such arrays on the heap.
> In any case, there is a very large variety of prior art in terms of
> language implementations that support variable length arrays on a variety
> of platforms.  For example, all Ada implementations support this.
> So does GNU C.

I accept the prior-art argument and the usefulness argument.

But I don't accept this part: 'the compiler could simply allocate such
arrays on the heap.'

The compiler may have to use a hidden auto-pointer-like mechanism for
removing such arrays from the heap in cases of function returns,
longjmp, and exceptions.  I expect this would be reasonable for function
returns and exceptions.  But it would be new functionality for
'longjmp'.

I say 'may have to' because every processor I know can implement
variable-sized stack frames by subtracting an appropriate value from
the stack pointer at the appropriate time.  But what about processors I
don't know about?  Are there truly any processors in use which don't
support subtracting a computed value from the stack pointer?

Michael Chastain
mec@duracef.shout.net
Check out my cool trace-and-replay debugger:
ftp://tsx-11.mit.edu/pub/linux/sources/usr.bin/mec-0.3.tar.gz
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