Can a 32 bit GCC running on a 64 bit Intel be made to emit SSE SIMD instructions automatically?

[Tim Prince]

On 5/19/2012 5:41 PM, Georg GCC user wrote:
> On Sat, May 19, 2012 at 11:57 PM, Tim Prince<n8tm@aol.com>  wrote:
>
>>> So, is there any way to make a 32 bit GCC emit mulpd and
>>> the like automatically (and correctly), without explicitly
>>> calling built-ins, like there is when everything is 64 bits?
>>> (Maybe: Does the vectorizer, if applicable, recognize that
>>> it may assume presence of suitable hardware and act
>>> accordingly?)
>>>
>>> VECTOR f(double a, double b, double c, double d)
>>> {
>>>    return (VECTOR) { a OP c, b OP d };
>>> }
>>>
>>> (VECTOR is an array of two 64 bit FPT components,
>>> in all GCC languages I have tried. It works nicely, as said,
>>> with 64 bit compilers.)
>> Did you consider a suitable -march setting?
> I tried dropping -march, and using -march=native, and -march=core2
> on this machine. -march=corei7 on another. Irrespective of the switches,
> there will be working executables. But they have two xxxsd instructions,
> which is unlike the single xxxpd the 64 bit compiler produces
> in the 64 bit OS/GCC environment. The programs run on the same
> physical processor. So the translated program does use SSE registers,
> but the code does not exercise the 128 bit pairs of doubles, only the
> 64 bit doubles. This creates a huge difference in speed (up to x2).
> Hence my question: Does a 32 bit GCC, unlike a 64 bit GCC,
> require explicitly calling intrinsics in the source program when
> the physical CPU is 64 bit? Or is there a way to cater to the
> vectorization circuits of a 32 bit GCC so that is will emit xxxpd?
>
> (The GCCs in the 32 bit software environments given won't accept -m64.)
>
> Georg
>
> Georg
Auto-vectorization should be enabled, as for x86_64, by setting a 
suitable -march and by setting -O3 or -O2 -ftree-vectorize.  The 
additional option -ftree-vectorizer-verbose=2 should give information as 
to why recognized loops aren't vectorized.

-- 
Tim Prince