[LLVMdev] Vectorization of pointer PHI nodes

[Renato Golin]

On 14 October 2013 19:31, Arnold Schwaighofer <aschwaighofer at apple.com>wrote:

> Renato, can you post the c code for the function and the assembly that gcc
> produces?
>

Attached.


Your initial example could be well handled by vectorization of strided
> loops (and the mentioning of VLD3(.8?)/VST3(.8?) lead me to assume that
> this is what happened). But the LLVM-IR you sent has a store of 0 in there
> ;) and strides by 4.
>

I think so. Ignore the last write, it was bogus. (but don't ignore the fact
that GCC vectorized it anyway with vst4!).

By running GCC with -ftree-vectorizer-verbose=1 I got:

test.c:11: note: create runtime check for data references DELTA and
*WRITE_30
test.c:11: note: create runtime check for data references *READ_29 and
*WRITE_30
test.c:11: note: created 2 versioning for alias checks.
test.c:11: note: === vect_do_peeling_for_loop_bound ===Setting upper bound
of nb iterations for epilogue loop to 14
test.c:11: note: LOOP VECTORIZED.

The result is a very concise and very dense code:

vld1.8 {d28[], d29[]}, [r5]
vld3.8 {d16, d18, d20}, [r9]!
vld3.8 {d17, d19, d21}, [r9]
vmvn  q3, q8
vmvn  q15, q9
vmvn  q8, q10
vsub.i8 q11, q3, q14
vsub.i8 q12, q15, q14
vsub.i8 q13, q8, q14
vst3.8 {d22, d24, d26}, [r8]!
vst3.8 {d23, d25, d27}, [r8]

cheers,
--renato
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