[llvm-dev] How to prevent clang/llvm from generating floating-point instructions?

[Xiaochu Liu via llvm-dev]

Hi Tim,

Thanks for your message! It turns out that the infrastructure (an
outdated one) that I am working on is using gcc+dragonegg to generate
llvm code:

gcc -m32 -S -c -O0 -fplugin=$(DRAGONEGG_SO)
-fplugin-arg-dragonegg-emit-ir $< -o $@.tmp

It directly generates llvm code with fadd, etc. I'm not familiar with
dragonegg plugin...

Thanks,
XIaochu




On Wed, Mar 16, 2016 at 12:00 PM, Tim Northover <t.p.northover at gmail.com> wrote:
> Hi Xiaochu,
>
> On 16 March 2016 at 11:49, Xiaochu Liu via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>> I was trying to compile a code with only integer type variables and
>> integer operations. Clang/llvm kept showing me llvm code with
>> floating-point instructions (fmul, fadd, fptosi, etc.). Is there a way
>> in Clang or llvm to stop the compiler from doing that? My experiment
>> does not allow floating-point operations...
>
> I think Clang's "-mno-implicit-float" is probably the option you want.
>
> I'm very surprised you're getting real floating operations like fadd
> if your source really contains no floats though (it's mostly only used
> implicitly for things like memcpy). So if that doesn't work, you
> should probably investigate where they're coming from more deeply.
> Maybe it's some external header you've included?
>
> Cheers.
>
> Tim.