[llvm-bugs] [Bug 26135] New: Cortex-A5 codegen suboptimal?

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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: unassignedbugs at nondot.org
          Reporter: tulipawn at gmail.com
                CC: llvm-bugs at 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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