llvm dev - Feb 2013 - [LLVMdev] Optimizer to remove duplicate loads?

Which optimizer would remove duplicate, or unneeded loads?  In my
generator I end up having a lot of the same load. For example here I
keep loading "@pt" which will always be the same value.

  %16 = load %1** @pt, align 8
  %17 = getelementptr inbounds %1* %16, i64 0, i32 2, i32 0
  %18 = load i32* %17, align 4
  call void @trace_integer(i32 %18)
  %19 = load %1** @pt, align 8
  %20 = getelementptr inbounds %1* %19, i64 0, i32 2, i32 1
  %21 = load i32* %20, align 4
  call void @trace_integer(i32 %21)
  %22 = load %1** @pt, align 8
  %23 = getelementptr inbounds %1* %22, i64 0, i32 0

-- 
edA-qa mort-ora-y
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Sign: Please digitally sign your emails.
Encrypt: I'm also happy to receive encrypted mail.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 261 bytes
Desc: OpenPGP digital signature
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20130224/75f66349/attachment.sig>

Hi,

On 24/02/13 06:48, edA-qa mort-ora-y wrote:
> Which optimizer would remove duplicate, or unneeded loads?  In my
> generator I end up having a lot of the same load. For example here I
> keep loading "@pt" which will always be the same value.
in order to do this, the optimizers need to know that the call to
@trace_integer does not modify the contents of @pt.  Is it logically
possible for them to deduce this?  If not, no optimizer can do what
you want.

Ciao, Duncan.
>
>    %16 = load %1** @pt, align 8
>    %17 = getelementptr inbounds %1* %16, i64 0, i32 2, i32 0
>    %18 = load i32* %17, align 4
>    call void @trace_integer(i32 %18)
>    %19 = load %1** @pt, align 8
>    %20 = getelementptr inbounds %1* %19, i64 0, i32 2, i32 1
>    %21 = load i32* %20, align 4
>    call void @trace_integer(i32 %21)
>    %22 = load %1** @pt, align 8
>    %23 = getelementptr inbounds %1* %22, i64 0, i32 0
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

On 24/02/13 09:02, Duncan Sands wrote:
> in order to do this, the optimizers need to know that the call to
> @trace_integer does not modify the contents of @pt.  Is it logically
> possible for them to deduce this?  If not, no optimizer can do what
> you want.
Yeah, I thought about that and then realized in this context they could
not (it's an external function). Is there some attribute I can mark the
functions with however that would allow the optimizers to understand
it's safe not to reload?

-- 
edA-qa mort-ora-y
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Sign: Please digitally sign your emails.
Encrypt: I'm also happy to receive encrypted mail.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 261 bytes
Desc: OpenPGP digital signature
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20130224/00de6c27/attachment.sig>