llvm dev - Jun 2012 - [LLVMdev] Instcombine increases the number of instructions?

Hello,
Can  the Instcombine pass  increase the number of instructions of a block?


-- 
*Rafael Parizi*
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Hi Rafael,
> Can  the Instcombine pass  increase the number of instructions of a block?
while it usually doesn't, in theory it can increase the number of LLVM IR
instructions.  I don't recall an example off the top of my head, but the
usual situation is that replacing some instruction I with a pair J, K
results in better code generation.  There are a small number of cases like
this.

Ciao, Duncan.

I perform the Instcombine pass over Rijndael benchmark from Mibench ( suite
of benchmarks). For compile, I use "-Instcount" for counting the
instructions. Comparing the bench without transformation with the
bench transformed
by instcombine, I perceived a 10% of increase in the number of
instructions. This is possible?

On Wed, Jun 27, 2012 at 4:57 AM, Duncan Sands <baldrick at free.fr> wrote:
> Hi Rafael,
>
> > Can  the Instcombine pass  increase the number of instructions of a
> block?
>
> while it usually doesn't, in theory it can increase the number of LLVM
IR
> instructions.  I don't recall an example off the top of my head, but
the
> usual situation is that replacing some instruction I with a pair J, K
> results in better code generation.  There are a small number of cases like
> this.
>
> Ciao, Duncan.
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>


-- 
*Rafael Parizi*
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