[llvm-dev] Clang/LLVM 5.0 optnone attribute with -O0

Craig Topper via llvm-dev llvm-dev at lists.llvm.org
Sun Sep 17 22:27:24 PDT 2017

To prevent optnone from being added you can replace -O0 with "-O1 -Xclang
-disable-llvm-passes". The -O1 will prevent the optnone, and the rest will
stop clang from performing any optimizations.


On Sun, Sep 17, 2017 at 10:12 PM, Diptorup Deb via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
> We have a research LLVM-based domain-specific code generator that we want
> to upgrade form LLVM 4.0 to 5.0. The code generator is written as an
> out-of-tree loadable module for opt.
> Till Clang 4.0 we were compiling the front-end code (annotated C++) using
> -O0. The generated bitcode was further processed using opt with our module
> loaded. In Clang 5.0 we see that using -O0 adds the optnone attribute to
> all functions, making it impossible to use any existing LLVM passes in our
> code generator.
> We also tried using -
> "clang -Xclang -load -Xclang <module>.so -mllvm <custom options>"
> , but this caused a segfault at llvm::legacy::FunctionPassMana
> gerImpl::doInitialization(llvm::Module&).
> What is the right way to get around this issue?
> Dipto
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