More SVE instructions

[maranget]

Add the AArch64 SVE instructions RDVL and ADDVL.

[murzinv]

LGTM :+1:

[maranget]

Hi @relokin, I am currently adding CNT and INC instructions, which look sufficient to write vector length independant code.

[maranget]

Hi @murzinv and @relokin. I'd be glad to have your opinion on the last two commits. Then, we can consider merging.

[murzinv]

which look sufficient to write vector length independant code

VL independent code usually done with loop partitioning, something like

AArch64 T
{
 uint32_t x[8] = {1,2,3,4,5,6,7,8};
 0:X0=x;
}
P0 ;
MOV X1,#0                      ;
MOV X2,#8                      ;
WHILELT P0.S,X1,X2             ;
L0:                            ;
LD1W {Z0.S},P0/Z,[X0,X1,LSL #2];
ADD Z0.S,Z0.S,Z0.S             ;
ST1W {Z0.S},P0,[X0,X1,LSL #2]  ;
INCW X1                        ;
WHILELT P0.S,X1,X2             ;
B.FIRST L0                     ;

forall x={2,4,6,8,10,12,14,16}

Which requires only INCW being implemented.

I'd be glad to have your opinion on the last two commits. Then, we can consider merging.

I'll have closer look after weekend

[maranget]

Hi @murzinv, I have added your test as V26. It works perfectly. Test V25 was inspired by compiler output...

[murzinv]

I could not find any issues with this PR other than few nipicks. LGTM :+1:

[murzinv]

Test V25 was inspired by compiler output...

Out of curiosity, could you share compiler input? :smile:

[maranget]

Test V25 was inspired by compiler output...

Out of curiosity, could you share compiler input? 😄

I'll look for it.

[maranget]

Thanks for your review @murzinv. Let us delay merge as I'd like to simplify history.

[maranget]

Test V25 was inspired by compiler output...

Out of curiosity, could you share compiler input? 😄

Compiler input:

#include <arm_sve.h>

void saxpy_c(int32_t *x, int32_t *y) {
        int i;
        for (i=0; i<1023; i++) {
                y[i] = x[i] + y[i];
        }
}

Original code is from this page. Compilation command is gcc -S -march=armv8-a+sve -O2 a.c on a MacBook M1.

% gcc --version
Apple clang version 15.0.0 (clang-1500.1.0.2.5)
Target: arm64-apple-darwin23.2.0
...

[murzinv]

Test V25 was inspired by compiler output...

Out of curiosity, could you share compiler input? 😄

Compiler input:

#include <arm_sve.h>

void saxpy_c(int32_t *x, int32_t *y) {
        int i;
        for (i=0; i<1023; i++) {
                y[i] = x[i] + y[i];
        }
}

Original code is from this page. Compilation command is gcc -S -march=armv8-a+sve -O2 a.c on a MacBook M1.

% gcc --version
Apple clang version 15.0.0 (clang-1500.1.0.2.5)
Target: arm64-apple-darwin23.2.0
...

Thanks! Interestingly that on that page their assembly output uses while* / inc* idiom, yet I can see that GCC can generate some form of it as well with upgrade to -O3. So, both V25 and V26 reflect real-world codegen.

[maranget]

Merged, thanks for teh review @murzinv.