https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83402
--- Comment #6 from Paul Clarke <pc at us dot ibm.com> ---
(In reply to Steven Munroe from comment #5)
> You need to look at the generated asm code. And see what the compiler is
> doing.
>
> Basically it should be generating a vspltisw vr,si for vec_splat_s32.
>
> But if the immediate signed int (si) is greater than 15, should failure with:
>
> error: argument 1 must be a 5-bit signed literal
I was hoping you'd tell me the scenario with which you saw that error. :-)
> The vec_splats should work for any value as it will load a const vector from
> storage.
>
> Perhaps the compiler is generating bad code and not reporting it.
>
> Or the compiler is too smart and converting the vec_splat_s32 to the more
> general vec_splats under the covers.
I think the compiler is doing this. Here's an extract from a (new) simple test
case:
--
out(a);
a = _mm_slli_epi32( a, 7 );
out(a);
a = _mm_slli_epi32( a, 31 );
out(a);
--
li r0,32
stvx v31,r1,r0
bl 10000628 <out+0x8>
addis r9,r2,-2
vspltisw v0,7
addi r9,r9,-30976
lvx v31,0,r9
vslw v31,v31,v0
xxlor vs34,vs63,vs63
bl 10000628 <out+0x8>
addis r9,r2,-2
addi r9,r9,-30960
lvx v2,0,r9
vslw v2,v31,v2
bl 10000628 <out+0x8>
--
So, if the shift value is < 16, it uses vspltisw.
If the shift value is >= 16, it loads a const vector from memory.
Is this issue now moot?
