llvm dev - Jan 2019 - Textual IR value names

And the clang behavior can be controlled with
-fdiscard-value-names/-fno-discard-value-names

~Craig


On Wed, Jan 9, 2019 at 2:16 PM Davide Italiano via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On Wed, Jan 9, 2019 at 2:12 PM David Greene via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> >
> > I like my LLVM IR text to have nice value names, e.g.
> >
> > %add = add ...
> > %mul = mul ...
> >
> > And this all works well if the build has asserts enabled.  If the
build
> > does not have asserts enabled, it's not so nice:
> >
> > %1 = add ...
> > %2 = mul ...
> >
> > I understand the use for obfuscating names, but the choice to make
this
> > dependent on whether or not asserts are enabled seems odd to me.  At
the
> > very least it's surprising.  It took some time for me to figure
out why
> > some of our builds behaved differently than others.
> >
> > Is this an intentional design choice?  If so, what's the
rationale?  If
> > not, would it make sense to add a CMake option to specify whether
> > textual IR preserves names or not rather than overloading
> > ENABLE_ASSERTIONS?
> >
>
> You can use `opt -instnamer`.
>
> --
> Davide
>
> "There are no solved problems; there are only problems that are more
> or less solved" -- Henri Poincare
> _______________________________________________
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> llvm-dev at lists.llvm.org
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Craig Topper via llvm-dev <llvm-dev at lists.llvm.org> writes:
> And the clang behavior can be controlled with -
> fdiscard-value-names/-fno-discard-value-names
That's a little better for users, but again, why should the default
behavior change based on whether or not asserts are enabled?

                          -David

The names are dropped to save memory when a release build of the compiler
is being used. This is what you probably want on a release compiler you
intend to ship since it should be faster. The NDEBUG check is an easy way
to tell the difference between release and debug builds. People probably
don't want to have to remember to set an additional cmake option to make a
release compiler faster.

The -fdiscard-value-names/-fno-discard-value-names was added about a year
ago https://reviews.llvm.org/D42887  not sure if there is more discussion
about the asserts behavior discussed there.

~Craig


On Wed, Jan 9, 2019 at 2:25 PM David Greene <dag at cray.com> wrote:
> Craig Topper via llvm-dev <llvm-dev at lists.llvm.org> writes:
>
> > And the clang behavior can be controlled with -
> > fdiscard-value-names/-fno-discard-value-names
>
> That's a little better for users, but again, why should the default
> behavior change based on whether or not asserts are enabled?
>
>                           -David
>
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