llvm dev - Jul 2011 - [LLVMdev] [cfe-dev] Exception Handling Rewrite Branch

For those who are playing along, I've started on the exception handling
rewrite following the document and comments from this thread:

	http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-July/041748.html

The repositories are:

	http://llvm.org/svn/llvm-project/llvm/branches/exception-handling-rewrite
	http://llvm.org/svn/llvm-project/cfe/branches/exception-handling-rewrite

Progress Report:

	I created the two new instructions: landingpad and resume. Hand-modified code
can run through the assembler and disassembler and emit the same code. The
verifier can verify basic properties of the landingpad instruction.

Next:

	I'll be working on getting inlining to work.

Feel free to respond with questions, comments, and concerns about the design.
Also, please take some time to review the patches I submit.

-bw

I have nothing to contribute other than to ask if this rewrite will bring
clang's -fno-exceptions behavior inline with GCC's. According to this
comment: http://llvm.org/bugs/show_bug.cgi?id=9171#c5 clang disables both C++
and Objective-C exceptions with that option whereas GCC only disables them for
C++. Of course, this may have already been fixed in clang in the 5 months since
I reported that bug, and WebKit fixed the issue where it was cropping up for
them, but I just wanted to bring it to your attention if you're going to
specifically change how exceptions are implemented in clang.

Of course this could be completely irrelevant, so carry on.


Jon Shier

On Jul 26, 2011, at 12:01 PM, Jon Shier wrote:
> I have nothing to contribute other than to ask if this rewrite will bring
clang's -fno-exceptions behavior inline with GCC's. According to this
comment: http://llvm.org/bugs/show_bug.cgi?id=9171#c5 clang disables both C++
and Objective-C exceptions with that option whereas GCC only disables them for
C++. Of course, this may have already been fixed in clang in the 5 months since
I reported that bug, and WebKit fixed the issue where it was cropping up for
them, but I just wanted to bring it to your attention if you're going to
specifically change how exceptions are implemented in clang.
> 
> Of course this could be completely irrelevant, so carry on.
It is :)

The exceptions rewrite concerns how exceptions are expressed in LLVM IR. It will
have no effect on Clang's behavior, except hopefully to eliminate some
miscompiles that have resisted our previous attempts to fix them.

	- Doug

<dropping cfe-dev>

On Jul 26, 2011, at 4:16 AM, Bill Wendling wrote:
> For those who are playing along, I've started on the exception handling
rewrite following the document and comments from this thread:
> 
> 	http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-July/041748.html
> 
> The repositories are:
> 
> 	http://llvm.org/svn/llvm-project/llvm/branches/exception-handling-rewrite
> 	http://llvm.org/svn/llvm-project/cfe/branches/exception-handling-rewrite
> 
> Progress Report:
> 
> 	I created the two new instructions: landingpad and resume. Hand-modified
code can run through the assembler and disassembler and emit the same code. The
verifier can verify basic properties of the landingpad instruction.
Hi Bill,

Any reason to do this on a branch?  Why can't the patches go into mainline?

-Chris

On Jul 26, 2011, at 11:00 PM, Chris Lattner wrote:
> On Jul 26, 2011, at 4:16 AM, Bill Wendling wrote:
> 
>> For those who are playing along, I've started on the exception
handling rewrite following the document and comments from this thread:
>> 
>> 	http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-July/041748.html
>> 
>> The repositories are:
>> 
>> 
http://llvm.org/svn/llvm-project/llvm/branches/exception-handling-rewrite
>> 
http://llvm.org/svn/llvm-project/cfe/branches/exception-handling-rewrite
>> 
>> Progress Report:
>> 
>> 	I created the two new instructions: landingpad and resume.
Hand-modified code can run through the assembler and disassembler and emit the
same code. The verifier can verify basic properties of the landingpad
instruction.
> 
> Hi Bill,
> 
> Any reason to do this on a branch?  Why can't the patches go into
mainline?
> 
Hi Chris,

Some of the changes (like the inliner changes) are going to break the old EH way
of doing things. The front-ends will need to change over to the new EH scheme.
And they won't want to change over until things are finished. It's a bit
of a chicken-and-egg thing. I figured that doing this on a branch first and then
outlining how to change the front-ends and/or create an Auto-upgrade tool would
be the best course of action.

-bw