[LLVMdev] PHIs with Same Basic Block Listed Twice

[Daniel Berlin]

On Tue, Mar 17, 2009 at 2:56 PM, Dale Johannesen <dalej at apple.com> wrote:
>
> On Mar 17, 2009, at 11:37 AMPDT, John Criswell wrote:
>
>> Dear All,
>>
>> I have, in an LLVM bitcode program, the following phi node:
>>
>> %iftmp.225.0 = phi i8* [ getelementptr ([10 x i8]* @.str12597431,
>> i32 0,
>> i32 0), %bb114 ], [ getelementptr ([10 x i8]* @.str1258, i32 0, i32
>> 0),
>> %bb111 ], [ getelementptr ([10 x i8]* @.str1258, i32 0, i32 0),
>> %bb111 ]
>>
>> This phi instruction has two arguments for the same incoming basic
>> block.  The only reason why it passes verification right now is
>> because
>> the same constant expression is used for the same basic block.
>>
>> Does anyone know what might be causing this phi to have the same
>> incoming block listed multiple times?  Should LLVM consider such a phi
>> valid?
>
> I'm pretty sure I've seen this where %bb111 ends in a switch that has
> two cases that both lead to this phi.
>

Does such a block have two outgoing edges?
IE if i walk the predecessors of  the successor, do i hit the same block twice?
If so, then PHI's with two arguments from the same block would be legal.

--Dan