llvm dev - Mar 2018 - opt: how to invoke optimizations manually?

Hello,

I'd like to measure the impact of optimizations.
Trying this (for DCE):

* clang -S -emit-llvm test.c
* opt -S test.ll > without_dce.ll
* opt -S -dce test.ll > with_dce.ll

gives without_dce.ll and with_dce.ll having the same content.

How can you apply certain optimizations in a specified order?

Best,
HwJ

---

$ cat test.c
> int dce(int n) {
>     if ((n < 0) || (n >= 0))
>         return 1;
> 
>     return 0;
> }

Hi,

You should add this option to the first command
*"-disable-O0-optnone"* so *clang
-Xclang -disable-O0-optnone -emit-llvm -S -o without_dce.ll test.c* then *opt
-dce -S < without_dce.ll > with_dce.ll*

HTH,

Son Tuan Vu

On Fri, Mar 16, 2018 at 2:15 PM, HwJ via llvm-dev <llvm-dev at
lists.llvm.org>
wrote:
> Hello,
>
> I'd like to measure the impact of optimizations.
> Trying this (for DCE):
>
> * clang -S -emit-llvm test.c
> * opt -S test.ll > without_dce.ll
> * opt -S -dce test.ll > with_dce.ll
>
> gives without_dce.ll and with_dce.ll having the same content.
>
> How can you apply certain optimizations in a specified order?
>
> Best,
> HwJ
>
> ---
>
> $ cat test.c
>
>> int dce(int n) {
>>     if ((n < 0) || (n >= 0))
>>         return 1;
>>
>>     return 0;
>> }
>>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Works. Thanks a lot!

On Fri, Mar 16, 2018 at 02:30:32PM +0100, Son Tuan VU
wrote:
>Hi,
>
>You should add this option to the first command
>*"-disable-O0-optnone"* so *clang
>-Xclang -disable-O0-optnone -emit-llvm -S -o without_dce.ll test.c* then
*opt
>-dce -S < without_dce.ll > with_dce.ll*
>
>HTH,
>
>Son Tuan Vu
>
>On Fri, Mar 16, 2018 at 2:15 PM, HwJ via llvm-dev <llvm-dev at
lists.llvm.org>
>wrote:
>
>> Hello,
>>
>> I'd like to measure the impact of optimizations.
>> Trying this (for DCE):
>>
>> * clang -S -emit-llvm test.c
>> * opt -S test.ll > without_dce.ll
>> * opt -S -dce test.ll > with_dce.ll
>>
>> gives without_dce.ll and with_dce.ll having the same content.
>>
>> How can you apply certain optimizations in a specified order?
>>
>> Best,
>> HwJ
>>
>> ---
>>
>> $ cat test.c
>>
>>> int dce(int n) {
>>>     if ((n < 0) || (n >= 0))
>>>         return 1;
>>>
>>>     return 0;
>>> }
>>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>

I feel like it might save people some significant time in the long run 
if opt printed a helpful little error message when it is instructed to 
run >0 transformation passes and also all functions it sees are optnone.

John



On 3/16/18 7:30 AM, Son Tuan VU via llvm-dev wrote:
> Hi,
> 
> You should add this option to the first command 
> *"-disable-O0-optnone"* so *clang -Xclang -disable-O0-optnone
-emit-llvm
> -S -o without_dce.ll test.c* then *opt -dce -S < without_dce.ll > 
> with_dce.ll*
> *
> *
> HTH,
> 
> Son Tuan Vu
> 
> On Fri, Mar 16, 2018 at 2:15 PM, HwJ via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
> 
>     Hello,
> 
>     I'd like to measure the impact of optimizations.
>     Trying this (for DCE):
> 
>     * clang -S -emit-llvm test.c
>     * opt -S test.ll > without_dce.ll
>     * opt -S -dce test.ll > with_dce.ll
> 
>     gives without_dce.ll and with_dce.ll having the same content.
> 
>     How can you apply certain optimizations in a specified order?
> 
>     Best,
>     HwJ
> 
>     ---
> 
>     $ cat test.c
> 
>         int dce(int n) {
>              if ((n < 0) || (n >= 0))
>                  return 1;
> 
>              return 0;
>         }
> 
>     _______________________________________________
>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>     http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>     <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> 
> 
> 
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>