[llvm-commits] patch: target option to disable tail calls

[Nick Lewycky]

On 18 January 2012 15:25, Eli Friedman <eli.friedman at gmail.com> wrote:

> On Wed, Jan 18, 2012 at 3:10 PM, Nick Lewycky <nlewycky at google.com> wrote:
> > The attached patch adds a new "-no-tail-calls" flag to llc, and
> implements
> > it in the x86 backend only. The intent is to support gcc's
> > -fno-optimize-sibling-calls in clang, which as far as I can tell just
> > disables tail calls period. The goal is to help ASAN produce correct
> stack
> > traces, which requires disabling all tail calls.
> >
> > As an aside, there is a good reason to do this in the backend and not at
> the
> > IR-level. The "tail" marker is used to indicate things that are useful to
> > the optimizers themselves; for example alias analysis interprets the
> > presence of a tail marker as proof that the callee can't access any
> alloca's
> > in the caller, whether the pointer has been captured or not.
>
> You're right that expressing this constraint with the tail marker
> doesn't make sense; that said, why not a function attribute?
>

Hunh? Why would you want to set this per-function? This is similar to
choosing (codegen) optimization levels or an ABIs, or other similar codegen
issues.

For my use-case, I want all functions to be built this way.

Nick
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