https://llvm.org/bugs/show_bug.cgi?id=26135
Bug ID: 26135
Summary: Cortex-A5 codegen suboptimal?
Product: libraries
Version: 3.7
Hardware: Other
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Backend: ARM
Assignee: unassignedb...@nondot.org
Reporter: tulip...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
It seems code generation for Cortex-A5 and armv7 doesn't provide much benefit,
sometimes even coming out a little slower (compared to default and v6
respectively).
Firstly, our old friend from issue #26106, w/o NEON and unrolling:
default cpu - v7, v6:
test sum_deque ... bench: 5,219 ns/iter (+/- 56), 4,967 ns/iter (+/-
50)
test sum_deque_2 ... bench: 3,272 ns/iter (+/- 40), 3,112 ns/iter (+/-
22)
It seems v6 code is faster on this cpu.
Secondly a few benchmarks, where the cortex-a5 target is either equal or
slower. (4-core)
Spectral-norm benchmark, v7:
$ time ./spectral 5500
default cpu cortex-a5
real 0m9.106s real 0m9.051s
user 0m34.110s user 0m34.240s
sys 0m0.040s sys 0m0.020s
Fannkuch benchmark:
$ time ./fannkuch 12
real 0m30.017s real 0m30.645s
user 1m55.570s user 1m56.350s
sys 0m0.030s sys 0m0.010s
Command used to compile:
rustc -C opt-level=3 -C target-feature=+v7 -C target-cpu=cortex-a5
Those were just a few examples off the top of my head, probably not the best
ones. I'm sure I've also seen an example or two benefiting from the cortex-a5
target but can't remember which.
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