[LLVMdev] LLVMdev Digest, Vol 86, Issue 5

[Peter Lawrence]

Bill et al,
                 I haven't really thought this through (I've never  
been a fan of exception specifications),
but it seems that inlining functions that do have exception  
specifications, and hence filter
operands in their landing-pads, isn't so obvious...

if  you want to  inline

	void foo () throw() { ... }		// empty throw() list means "no-throw"

into a function that does allow exceptions to be propagated out, then  
you'll have a hard time
combining their landing pads !

it seems, at least on first thought, that having more than one filter  
list in a landing pad isn't
useful ?  (assuming the only way to get more than one is from  
inlining ?)


-Peter Lawrence.



On Aug 3, 2011, at 12:35 AM, llvmdev-request at cs.uiuc.edu wrote:

>> yes there is something about the order :)  When front-ends output  
>> code, all
>> catches come before filters, but after inlining you can get:  
>> catches, filters,
>> catches, filters etc and this ordering needs to be preserved.   
>> Also, filters
>> are different from catches: filter ty_1, ty_2, ..., ty_N matches  
>> any exception
>> that would not be caught by any of ty_1, ty_2, ..., ty_N.  This is  
>> quite
>> different to filter ty_1, filter ty_2, ..., filter ty_N.  For  
>> example, suppose
>> you throw ty_2.  Then the filter ty_1, ty_2, ..., ty_N wouldn't  
>> match that,
>> but filter ty_1 would.
>>
>> So filter ty_1, ..., ty_N makes sense; but I don't think catch  
>> ty_1, ..., ty_N
>> makes sense.
>
> Agreed.  Other notes: a zero-type filter is meaningful (and pretty
> common ? it's the result of 'throw()'), but the ordering of the  
> cleanup
> bit is not, so I would suggest this grammar:
>
> Instruction ::= 'landingpad' Type 'personality' TypeAndValue  
> 'cleanup'? LandingPadClause*
> LandingPadClause ::= 'catch' TypeAndValue
> LandingPadClause ::= 'filter' TypeAndValue*
>
> John.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20110804/d7b3b31d/attachment.html>