llvm dev - Jan 2010 - [LLVMdev] [LLVMDev] Is there any way to eliminate zero-extension instruction?

Dear developers.

We try to make our own backend of llvm for our target machine.

Assume that we have the following code in our source code.

int i = ( a < b );

The code is translated into

r0 <- gt r1 r2
r3 <- and r0 0x1

We think that r3 is not necessary. Is there any way to eliminate it by just
modifying

our backend?

Thank you in advance.

Minwook Ahn
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On 20 Jan 2010, at 07:55, minwook Ahn wrote:
> Dear developers.
> 
> We try to make our own backend of llvm for our target machine.
> 
> Assume that we have the following code in our source code.
> 
> int i = ( a < b );
> 
> The code is translated into
> 
> r0 <- gt r1 r2
> r3 <- and r0 0x1
> 
> We think that r3 is not necessary. Is there any way to eliminate it by just
modifying
> 
> our backend?
> 
> Thank you in advance.
> 
> Minwook Ahn
Have you told LLVM the result of setcc operations is 0 or 1? Add the following
to the constructor of your ISelLowering class:

setBooleanContents(ZeroOrOneBooleanContent);

-- 
Richard Osborne | XMOS
http://www.xmos.com

Thank you for your reply.

In case of setcc, I saw it was removed.

But I could not delete the extension instruction in other cases of zero
extension from i1 to i32.

For example, in this case.

int main( int argc, char *argv[] ) {
   int i = ( argc > 0 ) & ( argv != NULL );
   return i;
}

So can you let us know how to remove it?

Thank you in advance.

Minwook Ahn

p.s. Sorry for the duplicated message if you get this twice.

2010/1/20 Richard Osborne <richard at xmos.com>
>
> On 20 Jan 2010, at 07:55, minwook Ahn wrote:
>
> > Dear developers.
> >
> > We try to make our own backend of llvm for our target machine.
> >
> > Assume that we have the following code in our source code.
> >
> > int i = ( a < b );
> >
> > The code is translated into
> >
> > r0 <- gt r1 r2
> > r3 <- and r0 0x1
> >
> > We think that r3 is not necessary. Is there any way to eliminate it by
> just modifying
> >
> > our backend?
> >
> > Thank you in advance.
> >
> > Minwook Ahn
>
> Have you told LLVM the result of setcc operations is 0 or 1? Add the
> following to the constructor of your ISelLowering class:
>
> setBooleanContents(ZeroOrOneBooleanContent);
>
> --
> Richard Osborne | XMOS
> http://www.xmos.com
>
>
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