llvm dev - Mar 2009 - [LLVMdev] [LLVMDev] trouble building gcc-frontend from source

Hi,
> Glad that works for you, but it means that if the 32-bit cost  
> computation overflows, we won't be told about it.   I think the right  
> thing is to make sure the computation saturates at 30 bits instead of  
> overflowing.  Am I going to talk myself into overloading operator+ ?
is this problem really real?  Or has LLVM been miscompiled?
The two people who have reported this were running very similar
systems with broken compiler versions...

Ciao,

Duncan.

On Mar 15, 2009, at 12:40 PM, Duncan Sands wrote:
> Hi,
>
>> Glad that works for you, but it means that if the 32-bit cost
>> computation overflows, we won't be told about it.   I think the
right
>> thing is to make sure the computation saturates at 30 bits instead of
>> overflowing.  Am I going to talk myself into overloading operator+ ?
>
> is this problem really real?  Or has LLVM been miscompiled?
> The two people who have reported this were running very similar
> systems with broken compiler versions...
Ah.  Probably not a real problem then; I was quite surprised it  
overflowed 30 bits, although it's certainly possible in theory.  I  
haven't seen any costs that come anywhere close to overflowing.  A  
broken host compiler would explain it nicely, I missed that.

On Mon, Mar 16, 2009 at 4:17 AM, Dale Johannesen <dalej at apple.com>
wrote:
>
> On Mar 15, 2009, at 12:40 PM, Duncan Sands wrote:
>
>> Hi,
>>
>>> Glad that works for you, but it means that if the 32-bit cost
>>> computation overflows, we won't be told about it.   I think the
right
>>> thing is to make sure the computation saturates at 30 bits instead
of
>>> overflowing.  Am I going to talk myself into overloading operator+
?
>>
>> is this problem really real?  Or has LLVM been miscompiled?
>> The two people who have reported this were running very similar
>> systems with broken compiler versions...
>
> Ah.  Probably not a real problem then; I was quite surprised it
> overflowed 30 bits, although it's certainly possible in theory.  I
> haven't seen any costs that come anywhere close to overflowing.  A
> broken host compiler would explain it nicely, I missed that.
>
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>
This is weird, because I tried it using the gcc-4.2 compiler too, and
it gave the same result. I'll probably try with Intel now. BTW,
changing the CC and CXX environment variables is the correct way to
change the compiler used for building llvm-gcc frontend right? (The
docs specified this method for changing the compiler while building
the llvm suite).