On 04/05/14 07:52, Marc Glisse wrote:
Hello,
we have front-end warnings about returning the address of a local
variable. However, quite often in C++, people don't directly return the
address of a temporary, it goes through a few functions which hide that
fact. After some inlining, the fact that we are returning the address of
a local variable can become obvious to the compiler, to the point where
I have used, for debugging purposes, grep 'return &' on the optimized
dump produced with -O3 -fkeep-inline-functions (I then had to sort
through the global/local variables).
fold_stmt looks like a good place for this, but it could go almost
anywhere. It has to happen after enough inlining / copy propagation to
make it useful though.
I was wondering if this would be better implemented as a propagation
problem so that cases where some, but not all paths to the return
statement have &local which reaches the return. ie
...
if (foo)
x = &local
else
x = &global
return x;
ISTM it ought to be a standard propagation problem and that the
problematical ADDR_EXPRs are all going to be in PHI nodes. So I think
you just search for problematical ADDR_EXPRs in PHI nodes as your seeds,
then forward propagate through the CFG. Ultimately looking for any
cases where those ADDR_EXPRs ultimately reach the return statement.
Thoughts?
jeff
