Re: Lots of FAILs in gcc.target/riscv/rvv/autovec/*

[Jeff Law <jeffreyalaw@gmail.com>]

On 11/7/23 21:31, Maxim Blinov wrote:
> I see, thanks for clarifying, that makes sense.
> 
> In that case, what about doing the inverse? I mean, are there unique
> patches in the vendor branch, and would it be useful to try to
> upstream them into master? My motivation is to get the best
> autovectorized code for RISC-V.
There should be nothing on the vendor branch that is not already on the 
trunk.  If there is, something has gone horribly wrong.

The process we've used over there is pretty simple.  Start with the 
gcc-13 branch, then cherry pick risc-v backend & testsuite changes from 
the trunk as well as limited target independent changes (primarily those 
which the risc-v backend depends on, or which we know/expect are 
important for risc-v for one reason or another).



> 
> I had a go at building the TSVC benchmark (in the llvm-test-suite[1]
> repository) both with the master and vendor branch gcc, and noticed
> that the vendor branch gcc generally beats master in generating more
> vector instructions.
> 
> If I simply count the number of instances of each vector instruction,
> the average across all 36 test cases of vendor vs master gcc features
> the following most prominent differences:
> 
> - vmv.x.s:        48 vs   0 (+ 48)
> - vle32.v:       150 vs  50 (+ 100)
> - vrgather.vv:    61 vs   0 (+ 61)
> - vslidedown.vi:  61 vs   0 (+ 61)
> - vse32.v:       472 vs 213 (+ 459)
> - vmsgtu.vi:      30 vs   0 (+ 30)
> - vadd.vi:        80 vs  30 (+ 50)
> - vlm.v:          18 vs   0 (+ 18)
> - vsm.v:          16 vs   0 (+ 16)
> - vmv4r.v:        21 vs   7 (+ 14)
> 
> (For reference, the benchmarks are all between 20k-30k in code size.
> Built with `-march=rv64imafdcv -O3`.)
> 
> Ofcourse that doesn't say anything about performance, but would it be
> possible/fair to say that the vendor branch may still be better than
> master for generating vectorized code for RISC-V?

> 
> What's interesting is that there's very little "regression" - I saw
> only very few cases where the vendor branch removed a vector
> instruction as compared to master gcc (the most often removed
> instruction by the vendor branch, as compared to master, is
> vsetvl/vsetvli.)
If the vendor branch is generating better code than the trunk then 
that's an indication that target independent changes on the trunk from 
the gcc-14 development cycle need some work ;)

Just comparing the static number of instructions isn't useful at all 
IMHO.  Now you can get dynamic instructions from various QEMU plugins at 
which point the data becomes much more interesting -- though you have to 
be careful interpreting that as well.


Jeff