llvm dev - Apr 2010 - [LLVMdev] understanding the opt tool

Hello,

I am trying to understand the opt tool. I wrote a program and created the
.bc file using clang. And I used this .bc file to generate another .bc file
using the opt tool. I dis-assembled this bitcode file and compared the
output with previous unoptimized bitcode file. It was the same. I am not
sure how to check the difference. Can anyone tell me if this is how we check
the optimized output or is there any other way. If the procedure that I used
is correct then could you tell me why am I not able to see the optimizations
on the source code. The commands are in this way:

clang -c -emit-llvm filename.c -o filename.bc

opt -strip-dead-prototypes -f <filename.bc> filename2.bc


I am working on the visual studio solution file and on windows 7 (in case
you want to know the platform)

Thanks.

-- 
Kalyan Ponnala
phone: 8163772059
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Hi Kalyan,
> opt -strip-dead-prototypes -f <filename.bc> filename2.bc
you have to specify the list of passes to run.  -strip-dead-prototypes
only removes unused declarations.  If there are none, it will do nothing.
Try:
   opt -std-compile-opts -f <filename.bc> filename2.bc

Ciao,

Duncan.

Hello Kalyan,

There is one more thing you should know:  Clang has maximum optimization turned
on by default.  You need to specify -O0 to turn it off if you want to see what
opt does without clang running all of the optimizations first.

--Sam



----- Original Message ----
> From: Duncan Sands <baldrick at free.fr>
> To: llvmdev at cs.uiuc.edu
> Sent: Sat, April 17, 2010 2:00:00 AM
> Subject: Re: [LLVMdev] understanding the opt tool
> 
> Hi Kalyan,
> opt -strip-dead-prototypes -f <filename.bc> 
> filename2.bc
you have to specify the list of passes to run.  
> -strip-dead-prototypes
only removes unused declarations.  If there are 
> none, it will do nothing.
Try:
   opt -std-compile-opts -f 
> <filename.bc> 
> filename2.bc
Ciao,

Duncan.
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