llvm dev - Nov 2012 - [LLVMdev] [cfe-dev] !!! 3.2 Release RC2 deadline November 29th

On 28 Nov 2012, at 17:02, Tanya Lattner wrote:
>> 14116 - Inliner incorrectly combines cleanup and catch landing pads
> 
> I think this one can be moved out as a release blocker. Too much debate and
no action on the bug in over a month.
This bug means that we can't compile at anything over -O1, or we get code
that does the wrong thing (e.g. terminate instead of catching an exception) if a
function with a cleanup is inlined into one with a catch (or possibly the other
way around).  I would really like to see it fixed for 3.2, because it results in
some fairly serious miscompilations.  I discussed it with a few people at the
DevMeeting.

David

On Nov 28, 2012, at 9:30 AM, David Chisnall <dc552 at cam.ac.uk> wrote:
> On 28 Nov 2012, at 17:02, Tanya Lattner wrote:
> 
>>> 14116 - Inliner incorrectly combines cleanup and catch landing pads
>> 
>> I think this one can be moved out as a release blocker. Too much debate
and no action on the bug in over a month.
> 
> This bug means that we can't compile at anything over -O1, or we get
code that does the wrong thing (e.g. terminate instead of catching an exception)
if a function with a cleanup is inlined into one with a catch (or possibly the
other way around).  I would really like to see it fixed for 3.2, because it
results in some fairly serious miscompilations.  I discussed it with a few
people at the DevMeeting.
So why isn't this caught by any of the regression testing (testsuite) if it
nothing above -O1 can be compiled? I assume you mean for your project?

I'm trying to understand how large of a problem this is. Ideally, we want
everything we can to get fixed.. but since there is some confusion and debate on
this bug, I'm thinking its not a quick or easy fix.

-Tanya

> 
> David

On 28 Nov 2012, at 19:41, Tanya Lattner wrote:
> So why isn't this caught by any of the regression testing (testsuite)
if it nothing above -O1 can be compiled? I assume you mean for your project?
Any Objective-C on non-Apple platforms that uses cleanups (including those Clang
inserts for blocks) breaks in certain cases with inlining.  There are also some
cases in C++, and cases in LTO (or using C headers in C++) when C++ code and C
code using __attribute__((cleanup)) are mixed.  We have an ugly hack in clang
that avoids it in the most common case, but there are almost certainly cases
that we are not catching.
> I'm trying to understand how large of a problem this is. Ideally, we
want everything we can to get fixed.. but since there is some confusion and
debate on this bug, I'm thinking its not a quick or easy fix.
There is no debate in the bug.  The consensus (both in the bug report and
in-person discussions at the DevMeeting) is that the inliner is doing an
obviously wrong thing when it takes a function containing a catchall and one
containing a cleanup, inlines one into the other, and ends up with one with just
a cleanup.  The discussion in the bug report is due to the fact that there are
probably also some corner cases where the wrong thing happens, but the inliner
bug is the serious one.

David