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

Chad Rosier mcrosier at apple.com
Wed Jan 18 17:15:05 PST 2012

Hi Nick,

>From the test case:

;CALL: test1:
;CALL-NOT: ret
;CALL: callq helper
;CALL: ret

Shouldn't it be:
; CALL-NOT: jmp

Also, we generally put a space between the semi-colon and the first letter of the check prefix (i.e., "; CALL-NOT").

Same comments for test2.

LGTM, otherwise.


On Jan 18, 2012, at 4:02 PM, Nick Lewycky wrote:

> On 18 January 2012 15:19, Chad Rosier <mcrosier at apple.com> wrote:
> Hi Nick,
> Why not something more like disable-tail-calls?  Most of the options begin with verbs such as Enable, Disable, Emit, Trap, etc.
> Sounds good, replaced all over. Updated patch attached!
> Nick
>  Chad
> On Jan 18, 2012, at 3:10 PM, Nick Lewycky 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.
> >
> > Please review!
> >
> > Nick
> >
> > <no-tail-calls-1.patch>_______________________________________________
> > llvm-commits mailing list
> > llvm-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> <no-tail-calls-2.patch>

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