[PATCH][PR16882] Ignore noreturn definitions when setting isPhysRegUsed.

[Eric Christopher]

Seems sane to me, Jim was one of the last people in here so he could
probably review as well.

-eric

On Tue, Sep 24, 2013 at 10:48 AM, Quentin Colombet <qcolombet at apple.com> wrote:
> Ping^3?
>
> -Quentin
>
> On Sep 17, 2013, at 10:54 AM, Quentin Colombet <qcolombet at apple.com> wrote:
>
> Ping^2?
>
> -Quentin
>
> On Sep 10, 2013, at 10:54 AM, Quentin Colombet <qcolombet at apple.com> wrote:
>
> Ping?
>
> -Quentin
>
> On Sep 3, 2013, at 2:16 PM, Quentin Colombet <qcolombet at apple.com> wrote:
>
> Hi,
>
> The proposed patch fixes PR16882:
> http://llvm.org/bugs/show_bug.cgi?id=16882.
> PR16882 reports a poor code generation issue where we were saving the link
> register before a call to a noreturn function, whereas it is not needed.
>
> Thanks for your reviews.
>
> ** Details **
>
> PEI inserts a save/restore sequence for the link register, according to the
> information it gets from the MachineRegisterInfo.
> MachineRegisterInfo is populated by the VirtRegMap pass.
> This pass was not aware of noreturn calls and was registering the
> definitions of these calls the same way as regular operations.
>
>
> ** Proposed Solution **
>
> Modify VirtRegPass so that it does not set the isPhysRegUsed information for
> registers only defined by noreturn calls.
> The rational is that a noreturn call is the "last instruction" of the
> program (if it returns the behavior is undefined), so everything that is
> defined by it cannot be used and will not interfere with anything else.
> Therefore, it is pointless to account for then.
>
>
> ** Experiments **
>
> I have made functional tests on x86_64 with O3 -fomit-frame-pointer on the
> llvm test-suite + SPEC.
> I did the same for ARMv7s.
>
> I have attached the performance numbers for ARMv7s (lower is better). These
> numbers only reports benches where the patch kicks in and the test runs for
> more than 1s (to avoid noise).
> The Reference column is LLVM r189613 and Test column is LLVM r189613 + the
> proposed patch.
>
> Cheers,
> -Quentin
> <virtreg.svndiff>
> <noreturn_perf.txt>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>