Re: [gentoo-user] USE="mmx mmxext sse sse2 ssse3 3dnow 3dnowext"

[Graham Murray <graham@gmurray.org.uk>]

Stroller <stroller@stellar.eclipse.co.uk> writes:

> But, surely "-march=" also instructs gcc to support the additional
> instructions.  Suggest you re-read Daniel's post that I was replying
> to.
>
> What's the difference between supporting the "certain set of
> instructions" with "-march=" and doing so with USEs?
>
> Or doesn't "-march=" support additional "certain sets of
> instructions". What does it do, then?

I am not sure,

$ gcc -Q --help=target -march=core2
The following options are target specific:         
  -m128bit-long-double                  [disabled] 
  -m32                                  [enabled]  
  -m3dnow                               [disabled] 
  -m3dnowa                              [disabled] 
  -m64                                  [disabled] 
  -m80387                               [enabled]  
  -m96bit-long-double                   [enabled]  
  -mabm                                 [disabled] 
  -maccumulate-outgoing-args            [disabled] 
  -maes                                 [disabled] 
  -malign-double                        [disabled] 
  -malign-functions=                               
  -malign-jumps=                                   
  -malign-loops=                                   
  -malign-stringops                     [enabled]  
  -march=                               core2      
  -masm=                                           
  -mavx                                 [disabled]
  -mbranch-cost=
  -mcld                                 [disabled]
  -mcmodel=
  -mcx16                                [disabled]
  -mfancy-math-387                      [enabled]
  -mfma                                 [disabled]
  -mforce-drap                          [disabled]
  -mfp-ret-in-387                       [enabled]
  -mfpmath=
  -mfused-madd                          [enabled]
  -mglibc                               [enabled]
  -mhard-float                          [enabled]
  -mieee-fp                             [enabled]
  -mincoming-stack-boundary=
  -minline-all-stringops                [disabled]
  -minline-stringops-dynamically        [disabled]
  -mintel-syntax                        [disabled]
  -mlarge-data-threshold=
  -mmmx                                 [disabled]
  -mms-bitfields                        [disabled]
  -mno-align-stringops                  [disabled]
  -mno-fancy-math-387                   [disabled]
  -mno-fused-madd                       [disabled]
  -mno-push-args                        [disabled]
  -mno-red-zone                         [disabled]
  -mno-sse4                             [enabled]
  -momit-leaf-frame-pointer             [disabled]
  -mpc
  -mpclmul                              [disabled]
  -mpopcnt                              [disabled]
  -mpreferred-stack-boundary=
  -mpush-args                           [enabled]
  -mrecip                               [disabled]
  -mred-zone                            [enabled]
  -mregparm=
  -mrtd                                 [disabled]
  -msahf                                [disabled]
  -msoft-float                          [disabled]
  -msse                                 [disabled]
  -msse2                                [disabled]
  -msse2avx                             [disabled]
  -msse3                                [disabled]
  -msse4                                [disabled]
  -msse4.1                              [disabled]
  -msse4.2                              [disabled]
  -msse4a                               [disabled]
  -msse5                                [disabled]
  -msseregparm                          [disabled]
  -mssse3                               [disabled]
  -mstack-arg-probe                     [disabled]
  -mstackrealign                        [enabled]
  -mstringop-strategy=
  -mtls-dialect=
  -mtls-direct-seg-refs                 [enabled]
  -mtune=
  -muclibc                              [disabled]
  -mveclibabi=