[LLVMdev] strict aliasing and LLVM

[Xinliang David Li]

On Fri, Oct 29, 2010 at 3:54 PM, Chris Lattner <clattner at apple.com> wrote:

> On Oct 29, 2010, at 11:35 AM, Xinliang David Li wrote:
>
> Thanks for the -m tip to pass llvm options.  Why is it not documented
> anywhere. See http://clang.llvm.org/docs/UsersManual.html#commandline
>
>
> -mllvm flags are somewhat equivalent to gcc -param options.  -mllvm flags
> are for compiler hackers to play with, and are not stable or documented.
>  Once TBAA is stable and reliable it will be controlled with
> -fstrict-aliasing as you'd expect.
>
>
-mllvm is also useful for passing options like -print-after=xxx.  May be it
should be mentioned when invoking 'clang --help-hidden'.

Thanks,

David



> -Chris
>
>
> <http://clang.llvm.org/docs/UsersManual.html#commandline>David
>
> On Fri, Oct 29, 2010 at 2:17 AM, Benjamin Kramer <benny.kra at googlemail.com
> > wrote:
>
>>
>> On 29.10.2010, at 09:26, Nick Lewycky wrote:
>>
>> >  * If clang -O2 worked by running 'opt' and 'llc' under the hood, we
>> > could tell it to pass a flag along to them, but it doesn't. As it
>> > stands, you can't turn -enable-tbaa on when running clang.
>> >
>> > So, putting that together, one way to do it is:
>> >
>> >   clang -O2 -fstrict-aliasing foo.c -flto -c -o foo.bc
>> >   opt -O2 -enable-tbaa foo.bc foo2.bc
>> >   llc -O2 -enable-tbaa foo2.bc -o foo2.s
>>
>> clang -O2 foo.c -S -o foo.s -mllvm -enable-tbaa
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