[Interest] Compiler optimisation flags on Android

[Mike Chinander]

>From https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

-Os
Optimize for size. -Os enables all -O2 optimizations that do not typically
increase code size. It also performs further optimizations designed to
reduce code size.
-Os disables the following optimization flags:

          -falign-functions  -falign-jumps  -falign-loops
          -falign-labels  -freorder-blocks  -freorder-blocks-algorithm=stc
          -freorder-blocks-and-partition  -fprefetch-loop-arrays


On Tue, May 3, 2016 at 12:00 PM, Nuno Santos <nunosantos at imaginando.pt>
wrote:

> I mean -O2, like the others
>
> Nuno Santos
> Founder / CEO / CTO
> www.imaginando.pt
> +351 91 621 69 62
>
> On 03 May 2016, at 06:27, Thiago Macieira <thiago.macieira at intel.com>
> wrote:
>
> On segunda-feira, 2 de maio de 2016 22:07:03 PDT Nuno Santos wrote:
>
> Hi,
>
> Below are the CFLAGS for Android
> (Qt/5.6/android_armv7/mkspecs/android-g++/qmake.conf)
>
> I’m wondering why there are no optimisation settings for arm rather than
> size. Is there any specific reason?
>
>
> Why should there be?
>
> } else { # arm
>    QMAKE_CFLAGS_RELEASE                   = -Os -fomit-frame-pointer
> -fno-strict-aliasing -finline-limit=64
>    QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO   = -g -Os -fomit-frame-pointer
>    -fno-strict-aliasing -finline-limit=64
>    QMAKE_CFLAGS_DEBUG                     = -g -marm -O0 -fno-omit-frame-
>    pointer
>    equals(ANDROID_TARGET_ARCH, armeabi):if(equals(NDK_TOOLCHAIN_VERSION,
> 4.8)|equals(NDK_TOOLCHAIN_VERSION, 4.9)) {
>        DEFINES += QT_OS_ANDROID_GCC_48_WORKAROUND
>    } else {
>        QMAKE_CFLAGS_RELEASE += -mthumb
>        QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += -mthumb
>    }
> }
>
>
> This section you pasted contradicts your statement. There are more
> optimisation flags besides -Os.
>
> --
> Thiago Macieira - thiago.macieira (AT) intel.com
>  Software Architect - Intel Open Source Technology Center
>
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