[LLVMdev] r98459 break of ExceptionDemo

[Garrison Venn]

Ok, I've isolated the recent additions that cause the issue and supplied a patch which is NOT meant
to be applied, but instead solely exists for identification purposes for those who know what they are doing. :-)
The patch is offset from HEAD.

The patch is a hack which removes use of the MCSymbol::isDefined(...) method, as its use happens to break
in the exception JIT context; both in MachineModuleInfo.:: TidyLandingPads(...) and in JITDwarfException::
EmitFrameMoves(...). In this context these symbols are not defined but rather are temporaries. Beyond this
I don't understand what the correct replacement is, or whether or not the use of MCSymbol::isDefined(...) can be 
dropped from TidyLandingPads(...) since there are probably other dependencies.  In 2.7 JITDwarfException::
EmitFrameMoves(...) used to check if the associated label id was deleted or folded into another. I guess the
intent may now be to have this happen automatically to MCSymbol instances?

I understand that trunk is being heavily thrashed in this area. Do you want me to turn ExceptionDemo into a related unit
test case even though it only works on x86/x86_64 on UNIX systems, and requires exceptions to be turned on?

Garrison

On Mar 18, 2010, at 14:41, Garrison Venn wrote:

> Forgot to add platform with issue: OS X 10.6.2. I have not tested elsewhere. 
> 
> Garrison
> 
> On Mar 18, 2010, at 14:20, Garrison Venn wrote:
> 
>> Hi Chris,
>> 
>> The MCSymbol r98459 patch of llvm seems to have broken the ExceptionDemo example. As the example is dying in the
>> associated personality's first unwind search phase, which happens to have no language specific context, and is returning
>> a _URC_CONTINUE_UNWIND, I believe the issue is generic and not specific to the example. However I'm not sure why then
>> this wasn't seen in one of the test cases. Anyway just wanted to give a heads up as I'm studying this, just in case the problem
>> is obvious to you. One way to reproduce this in trunk from root is to:
>> 
>> 1) set environment var BUILD_EXAMPLES 1
>> 
>> 2) svn switch -r 98458 http://llvm.org/svn/llvm-project/llvm/trunk
>> 3) make
>> 4) Debug/examples/ExceptionDemo 2
>> 5) example will complete successfully
>> 
>> 6) svn switch -r 98459 http://llvm.org/svn/llvm-project/llvm/trunk
>> 7) make
>> 8) Debug/examples/ExceptionDemo 2
>> 9) example will segv
>> 
>> Sorry I'm late identifying this. I'll keep on trying to isolate it further, though I'm guessing that the sensitivity is in JITDwarfEmitter.
>> 
>> Garrison
>> 
>> PS: Patch ref: http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20100308/097798.html
> 

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