[llvm-dev] clang optimizations

[via llvm-dev]

Hi Florian,

 

Thank you for your quick response. This fixes the optimization.

 

Best regards,

 

Viorel

 

From: Florian Hahn <florian_hahn at apple.com> 
Sent: Monday, January 25, 2021 1:58 PM
To: viorel.preoteasa at gmail.com; llvm-dev <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] clang optimizations

 

Hi,





On Jan 25, 2021, at 11:48, via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> > wrote:

 

Hello,

 

I am trying to apply level 3 of optimizations to a simple program. If I run:

 

clang -S -O3 -emit-llvm test.cpp -o testo.ll

 

all seems OK, the result testo.ll is highly optimized.

 

However if I attempt the same using:

 

clang -S -emit-llvm test.cpp -o a.ll

              opt-10 -S --O3 a.ll -o test.ll

 

 

Please take a look at the attributes added to the functions: https://godbolt.org/z/fs9f8n . Without optimizations (-O0), Clang will add `optnone` to the functions, effectively disabling optimizations when you run `opt`. If you don’t want clang to run optimizations, but not add `optnone`, you can use `clang -O3 -emit-llvm -S -mllvm -disable-llvm-optzns`.

 

Cheers,

Florian 

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