On Thursday, 24 January 2013 at 00:01:26 UTC, Walter Bright wrote:
On 1/23/2013 2:15 PM, Stephan wrote:
What would be the prototypic short program that simulates
referencing an out of
scope stack frame? It would be great to see an example that
produces a
deterministic segfault.
Just return a pointer to a local (first passing it through
another function in order to hide what you're doing from the
compiler).
btw, bug 8832 is an example of one.
OK, I spent quite a while to narrow it down, and I definitely can
say that there is a compiler bug related to the optimization
switch.
I filed an issue: (9387).
I could not anymore reproduce a seg-fault, but even worse: The
optimization switch changes the behavior of the program!, I
declared it as "major", since it is not clear whether this bug is
even detectable if it doesn't cause a seg-fault. It just changes
the behavior, so it seems to me very dangerous!
The program I attached in the bug-report is an implementation of
a minimization routine from Numerical Recipes, 3rd edition. This
bug is possibly caused by having a large number of local
variables, which are somehow written out into memory before moved
into registers or something. I looked at the assembly with a
colleague but we couldn't find something conclusive.
I hope that you guys can reproduce the bug (simply run "rdmd -O
brent_test.d" and compare it with "rdmd brent_test.d") on dmd
2.061. There is nothing exotic in the source-code, only
assignments. No pointers, no references, no structs. It must be a
compiler bug.
Stephan
