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Thread: GCC 4.9 Shows Little Change For AMD's Kaveri

  1. #1
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    Default GCC 4.9 Shows Little Change For AMD's Kaveri

    Phoronix: GCC 4.9 Shows Little Change For AMD's Kaveri

    Our latest Linux benchmarks of AMD's new "Kaveri" APU with Steamroller processor cores is comparing the GCC 4.8.2 compiler performance to the very latest GCC 4.9 compiler snapshot to see how the performance is fairing for this next Free Software Foundation compiler release due out within the next few months.

    http://www.phoronix.com/vr.php?view=19783

  2. #2
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    "-Ofast" will almost certainly give you faster binaries. You just need to be sure your code is "fast-math" safe.

  3. #3
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    Quote Originally Posted by s_j_newbury View Post
    "-Ofast" will almost certainly give you faster binaries. You just need to be sure your code is "fast-math" safe.
    What does this mean and how does one accomplish this? I'm just trying to learn here!

  4. #4
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    Quote Originally Posted by Tgui View Post
    What does this mean and how does one accomplish this? I'm just trying to learn here!
    ffast-math makes some assuptions about float math which can lead to faster code and loss of precision. see the gcc manual about it.

  5. #5
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    Quote Originally Posted by Tgui View Post
    What does this mean and how does one accomplish this? I'm just trying to learn here!
    -O3 vs -Ofast

    @@ -23,7 +23,7 @@
    -fcrossjumping [enabled]
    -fcse-follow-jumps [enabled]
    -fcx-fortran-rules [disabled]
    - -fcx-limited-range [disabled]
    + -fcx-limited-range [enabled]
    -fdata-sections [disabled]
    -fdce [enabled]
    -fdefer-pop [enabled]
    @@ -35,7 +35,7 @@
    -fearly-inlining [enabled]
    -fexceptions [disabled]
    -fexpensive-optimizations [enabled]
    - -ffinite-math-only [disabled]
    + -ffinite-math-only [enabled]
    -ffloat-store [disabled]
    -fforward-propagate [enabled]
    -fgcse [enabled]
    @@ -73,7 +73,7 @@
    -floop-nest-optimize [disabled]
    -floop-parallelize-all [disabled]
    -floop-strip-mine [disabled]
    - -fmath-errno [enabled]
    + -fmath-errno [disabled]
    -fmerge-all-constants [disabled]
    -fmerge-constants [enabled]
    -fmodulo-sched [disabled]
    @@ -127,7 +127,7 @@
    -fshort-wchar [disabled]
    -fshrink-wrap [enabled]
    -fsignaling-nans [disabled]
    - -fsigned-zeros [enabled]
    + -fsigned-zeros [disabled]
    -fsingle-precision-constant [disabled]
    -fsplit-ivs-in-unroller [enabled]
    -fsplit-wide-types [enabled]
    @@ -136,7 +136,7 @@
    -fthread-jumps [enabled]
    -fno-threadsafe-statics [enabled]
    -ftoplevel-reorder [enabled]
    - -ftrapping-math [enabled]
    + -ftrapping-math [disabled]
    -ftrapv [disabled]
    -ftree-bit-ccp [enabled]
    -ftree-builtin-call-dce [enabled]
    @@ -180,7 +180,7 @@
    -funroll-all-loops [disabled]
    -funroll-loops [disabled]
    -funsafe-loop-optimizations [disabled]
    - -funsafe-math-optimizations [disabled]
    + -funsafe-math-optimizations [enabled]
    -funswitch-loops [enabled]
    -funwind-tables [disabled]
    -fvar-tracking [enabled]

  6. #6
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    Quote Originally Posted by Tgui View Post
    What does this mean and how does one accomplish this? I'm just trying to learn here!
    It will violate the IEEE standard in subtle ways that usually doesn't matter. The same setting on the intel compiler is enabled by default.
    Last edited by carewolf; 02-01-2014 at 07:39 AM.

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