[Bug other/54857] New: Superfluous NOPs on Atom

[piotr.wyderski at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54857



             Bug #: 54857

           Summary: Superfluous NOPs on Atom

    Classification: Unclassified

           Product: gcc

           Version: 4.7.1

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: other

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: piotr.wyder...@gmail.com





GCC [4.7.1 on Linux and 4.6.1 on Cygwin] generates a LOT of unnecessary

NOPs when the target is Atom. The following testcase shows the odd behaviour:



int func(float f) { return (int)f; };



The output is:



gcc -S -O2 -march=atom -mtune=atom test.cpp 



.LFB0:

    .cfi_startproc

    cvttss2si    %xmm0, %eax

    nop

    nop

    nop

    nop

    nop

    nop

    ret

    .cfi_endproc 



When the target is e.g. Core2:



gcc -S -O2 -march=core2 -mtune=core2 test.cpp



it is simply:



.LFB0:

    .cfi_startproc

    cvttss2si    %xmm0, %eax

    ret

    .cfi_endproc 





gcc -v

Using built-in specs.

COLLECT_GCC=gcc

COLLECT_LTO_WRAPPER=/mnt/local/a3d.gcc-4.7.1/libexec/gcc/x86_64-unknown-linux-gnu/4.7.1/lto-wrapper

Target: x86_64-unknown-linux-gnu

Configured with: ../gcc-4.7.1/configure --prefix=/mnt/local/a3d.gcc-4.7.1

--with-gmp=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites

--with-mpfr=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites

--with-mpc=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites

--with-ppl=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites

--with-cloog=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites

--with-local-prefix=/mnt/local/a3d.gcc-4.7.1 --enable-languages=c,c++

--disable-multilib

Thread model: posix

gcc version 4.7.1 (GCC)