How to verify VFPv4 feature in ARM toolchain

Question

I have a pre-compiled ARM tool chain for a Cortex A15. I want to check whether it generate correct VFPv4 instructions. Any body have any ideas?

Answer 1

We can look it up in gcc release log which states

...
GCC now supports VFPv4-based FPUs and FPUs with single-precision-only VFP.
...

We can also verify it manually. According to ARM Architecture manual VFPv4 at least added Vector Fused Multiply Accumulate / Subtract.

void test_vfp4() {
    asm("VFMA.F32 q1, q2, q3");
}

Compiling this with -mfpu=neon-vfpv4 switch (otherwise my tool chain says Error: selected processor does not support ARM mode 'vfma.f32 q1,q2,q3')

gcc -mfpu=neon-vfpv4 -O2 -marm -c vfpv4.c

and dumping the binary for with

arm-linux-gnueabihf-objdump -S vfpv4.o 

should list below

00000000 <test_vfp4>:
   0:   f2042c56    vfma.f32    q1, q2, q3
   4:   e12fff1e    bx  lr

However I don't know how you can use this at C level since I couldn't find any intrinsic listed for these fused instructions or think of any other way.