llvm dev - Jul 2008 - [LLVMdev] InstructionCombining forgets alignment of globals

Hi Nicolas,
>   if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
> 
>     unsigned Align = GV->getAlignment();
> 
>     if (Align == 0 && TD &&
GV->getType()->getElementType()->isSized())
> 
>       Align =
TD->getPrefTypeAlignment(GV->getType()->getElementType());
>
> It assumes that global values are always optimally aligned. I think this is
> incorrect and the bottom two lines should be removed.
I don't understand - if Align is zero it means that GV was marked
as having preferred alignment (that's what Align == 0 means), so
it is not wrong to change it explicitly to the preferred alignment
for the target.

Ciao,

Duncan.

Hi Duncan,

I see. I didn't know GlobalValue had a method for changing the alignment
(and that 0 meant natural alignment). Explicitly calling setAlignment works
like a charm.

So it's not an LLVM bug.

Thanks,

Nicolas


-----Original Message-----
From: Duncan Sands [mailto:baldrick at free.fr] 
Sent: Thursday, 10 July, 2008 14:41
To: llvmdev at cs.uiuc.edu
Cc: Nicolas Capens
Subject: Re: [LLVMdev] InstructionCombining forgets alignment of globals

Hi Nicolas,
>   if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
> 
>     unsigned Align = GV->getAlignment();
> 
>     if (Align == 0 && TD &&
GV->getType()->getElementType()->isSized())
> 
>       Align =
TD->getPrefTypeAlignment(GV->getType()->getElementType());
>
> It assumes that global values are always optimally aligned. I think this
is
> incorrect and the bottom two lines should be removed.
I don't understand - if Align is zero it means that GV was marked
as having preferred alignment (that's what Align == 0 means), so
it is not wrong to change it explicitly to the preferred alignment
for the target.

Ciao,

Duncan.

On Thursday 10 July 2008 07:46, Nicolas Capens wrote:
> Hi Duncan,
>
> I see. I didn't know GlobalValue had a method for changing the
alignment
> (and that 0 meant natural alignment). Explicitly calling setAlignment works
> like a charm.
Nicolas,

Where are you explicitly calling setAlignment?  From llvm-gcc code?

                                           -Dave