[AArch64] Unrolling of loops with vector instructions. (#147420)
This patch permits loops with vector instructions to be unrolled.
Today there is an early exit in `getUnrollingPreferences()` of AArch64
targets if a vector instruction is observed in any of the loop blocks.
This patch fixes that so common loops like this one get a chance to be
unrolled:
void saxpy (float * dst, const float * src, const float a, const int
len) {
float32x4_t * vdst = (float32x4_t *)dst;
float32x4_t * vsrc = (float32x4_t *)src;
float32x4_t vk = vdupq_n_f32(a);
for (int i = 0; i < (len >> 2); i++)
{
vdst[i] = vaddq_f32(vdst[i], vmulq_f32(vsrc[i], vk));
}
}
Auto-vectorized loops are still not unrolled, unless they were not
interleaved when vectorized.
The provided test case shows the enhancement on top of runtime/partial
unrolling, depending on the CPU.
PR: https://github.com/llvm/llvm-project/pull/147420
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