I am looping through all instructions in a Function and depending on
what I found I may or may not insert code. Despite the fact that I'm
only actually inserting *before* instruction I have a infinite loop
when I do something like below. For awhile it was simple enough to
just increment i enough times but now I need something better.
for(inst_iterator i = inst_begin(F); i != inst_end(F); ++i) {
...
// possible insertions of unknown size
...
}
I tried storing the storing the initial iterator and reverting back to
it(along with storing the next element) and I am still left with a
infinite loop. I see some discussion online about weather insertions
with iterators in C++ is allowed period, so what is the correct way to
do something like this in LLVM? This must be a common problem.
Thank you
On Aug 29, 2011, at 12:38 PM, ret val wrote:> I am looping through all instructions in a Function and depending on > what I found I may or may not insert code. Despite the fact that I'm > only actually inserting *before* instruction I have a infinite loop > when I do something like below. For awhile it was simple enough to > just increment i enough times but now I need something better. > > for(inst_iterator i = inst_begin(F); i != inst_end(F); ++i) { > ... > // possible insertions of unknown size > ... > } > > I tried storing the storing the initial iterator and reverting back to > it(along with storing the next element) and I am still left with a > infinite loop. I see some discussion online about weather insertions > with iterators in C++ is allowed period, so what is the correct way to > do something like this in LLVM? This must be a common problem. >Have you tried this? for(inst_iterator i = inst_begin(F); i != inst_end(F); ) { Instruction *Inst = *i++; ... // possible insertions of unknown size ... } ? -bw
On Mon, Aug 29, 2011 at 12:38 PM, ret val <retval386 at gmail.com> wrote:> I am looping through all instructions in a Function and depending on > what I found I may or may not insert code. Despite the fact that I'm > only actually inserting *before* instruction I have a infinite loop > when I do something like below. For awhile it was simple enough to > just increment i enough times but now I need something better. > > for(inst_iterator i = inst_begin(F); i != inst_end(F); ++i) { > ... > // possible insertions of unknown size > ... > } > > I tried storing the storing the initial iterator and reverting back to > it(along with storing the next element) and I am still left with a > infinite loop. I see some discussion online about weather insertions > with iterators in C++ is allowed period, so what is the correct way to > do something like this in LLVM? This must be a common problem. >In general, this sort of thing depends on the container you're iterating over. Different containers have different iterator invalidation semantics. In this case, probably what you need to do is: i = insert(i, ...); containers backed by contiguous sequences (like std::vector, and I assume the inst list - but I could be wrong) can invalidate all iterators on insertion (since they might need to reallocate memory - moving all the contents of the vector to a new, larger, buffer) - so generally they give you a new, valid iterator as a return result from any insertion operation. (I assume your infinite loop that occured when you reset the iterator back to the start was caused by your own algorithm repeatedly inserting/restarting over and over again, and not by weirdness surrounding insertion iterator invalidation semantics) [also note that the LLVM coding guidelines suggest storing end once & then using that in eahc loop iteration - you should do this, but you'll hit iterator invalidation on insertion for the end iterator too, so you'll have to re-initialize it after any insertion that might invalidate the end iterator] - David -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20110829/c8193bcd/attachment.html>
That just gives me "error: cannot convert ‘llvm::Instruction’ to ‘llvm::Instruction*’ in initialization" I'm guessing you ment Instruction *Inst = &*i++; Which also leaves me with a infinite loop Thanks On Mon, Aug 29, 2011 at 3:52 PM, Bill Wendling <wendling at apple.com> wrote:> > On Aug 29, 2011, at 12:38 PM, ret val wrote: > >> I am looping through all instructions in a Function and depending on >> what I found I may or may not insert code. Despite the fact that I'm >> only actually inserting *before* instruction I have a infinite loop >> when I do something like below. For awhile it was simple enough to >> just increment i enough times but now I need something better. >> >> for(inst_iterator i = inst_begin(F); i != inst_end(F); ++i) { >> ... >> // possible insertions of unknown size >> ... >> } >> >> I tried storing the storing the initial iterator and reverting back to >> it(along with storing the next element) and I am still left with a >> infinite loop. I see some discussion online about weather insertions >> with iterators in C++ is allowed period, so what is the correct way to >> do something like this in LLVM? This must be a common problem. >> > Have you tried this? > > for(inst_iterator i = inst_begin(F); i != inst_end(F); ) { > Instruction *Inst = *i++; > ... > // possible insertions of unknown size > ... > } > > ? > > -bw > >
When I'm iterating through I only directly add BitCastInsts and a single CallInst(Im assuming the functions I also created are elsewhere). Unfortunately it doesnt look like theres is a good way to convert between the the iterator I and a CallInst *. Am I missing something? Thanks On Mon, Aug 29, 2011 at 3:59 PM, David Blaikie <dblaikie at gmail.com> wrote:> > > On Mon, Aug 29, 2011 at 12:38 PM, ret val <retval386 at gmail.com> wrote: >> >> I am looping through all instructions in a Function and depending on >> what I found I may or may not insert code. Despite the fact that I'm >> only actually inserting *before* instruction I have a infinite loop >> when I do something like below. For awhile it was simple enough to >> just increment i enough times but now I need something better. >> >> for(inst_iterator i = inst_begin(F); i != inst_end(F); ++i) { >> ... >> // possible insertions of unknown size >> ... >> } >> >> I tried storing the storing the initial iterator and reverting back to >> it(along with storing the next element) and I am still left with a >> infinite loop. I see some discussion online about weather insertions >> with iterators in C++ is allowed period, so what is the correct way to >> do something like this in LLVM? This must be a common problem. > > In general, this sort of thing depends on the container you're iterating > over. Different containers have different iterator invalidation semantics. > In this case, probably what you need to do is: > > i = insert(i, ...); > > containers backed by contiguous sequences (like std::vector, and I assume > the inst list - but I could be wrong) can invalidate all iterators on > insertion (since they might need to reallocate memory - moving all the > contents of the vector to a new, larger, buffer) - so generally they give > you a new, valid iterator as a return result from any insertion operation. > (I assume your infinite loop that occured when you reset the iterator back > to the start was caused by your own algorithm repeatedly > inserting/restarting over and over again, and not by weirdness surrounding > insertion iterator invalidation semantics) > [also note that the LLVM coding guidelines suggest storing end once & then > using that in eahc loop iteration - you should do this, but you'll hit > iterator invalidation on insertion for the end iterator too, so you'll have > to re-initialize it after any insertion that might invalidate the end > iterator] > - David >