build: detect arm32 assembly by default

[Raimo33]

This PR addresses issue #1751 by adding a call to check_arm32_assembly() by default, matching the current behavior with check_x86_64_assembly().

This would result in speedup on field_10x26_impl.h on default builds. For example, currently, the Bitcoin Core reference implementation compiles libsecp256k1 with default options, leading to unoptimal builds.

This change could help address bitcoin/bitcoin#32832 partially, considering the flamegraph shows that ecdsa_verify takes 90% of IBD time.

Benchmark	Avg(us) OFF	Avg(us) arm32	Improvement (%)
ecdsa_verify	379.0	322.0	15.0
ecdsa_sign	184.0	170.0	7.6
ec_keygen	160.0	145.0	9.4
ecdh	382.0	332.0	13.1
schnorrsig_sign	162.0	148.0	8.6
schnorrsig_verify	380.0	323.0	15.0
ellswift_encode	109.0	95.1	12.7
ellswift_decode	60.2	50.8	15.6
ellswift_keygen	268.0	240.0	10.4
ellswift_ecdh	395.0	343.0	13.2

[hebasto]

This would result in speedup on field_10x26_impl.h on default builds.

Please provide benchmarks to support this statement.

[Raimo33]

Please provide benchmarks to support this statement.

will do. I'm buying a raspberry PI right now. I reckon if the benchmarks don't show improvements we should delete field_10x26_arm.s entirely

[hebasto]

Perhaps convert this to a draft while the CI is red?

[Raimo33]

Please provide benchmarks to support this statement.

I've ran benchmarks on my raspberry pi 4. Here are the results.

Optional features:
assembly ............................ OFF

Benchmark                     ,    Min(us)    ,    Avg(us)    ,    Max(us)    

ecdsa_verify                  ,   378.0       ,   379.0       ,   379.0    
ecdsa_sign                    ,   184.0       ,   184.0       ,   185.0    
ec_keygen                     ,   160.0       ,   160.0       ,   160.0    
ecdh                          ,   382.0       ,   382.0       ,   383.0    
schnorrsig_sign               ,   162.0       ,   162.0       ,   162.0    
schnorrsig_verify             ,   380.0       ,   380.0       ,   381.0    
ellswift_encode               ,   109.0       ,   109.0       ,   109.0    
ellswift_decode               ,    60.1       ,    60.2       ,    60.3    
ellswift_keygen               ,   268.0       ,   268.0       ,   268.0    
ellswift_ecdh                 ,   395.0       ,   395.0       ,   395.0

Optional features:
assembly ............................ arm32

Benchmark                     ,    Min(us)    ,    Avg(us)    ,    Max(us)    

ecdsa_verify                  ,   322.0       ,   322.0       ,   322.0    
ecdsa_sign                    ,   170.0       ,   170.0       ,   170.0    
ec_keygen                     ,   145.0       ,   145.0       ,   145.0    
ecdh                          ,   332.0       ,   332.0       ,   333.0    
schnorrsig_sign               ,   148.0       ,   148.0       ,   149.0    
schnorrsig_verify             ,   323.0       ,   323.0       ,   324.0    
ellswift_encode               ,    94.9       ,    95.1       ,    95.3    
ellswift_decode               ,    50.6       ,    50.8       ,    50.9    
ellswift_keygen               ,   239.0       ,   240.0       ,   240.0    
ellswift_ecdh                 ,   343.0       ,   343.0       ,   343.0

[hebasto]

I've ran benchmarks on my raspberry pi 4. Here are the results.

Which compiler did you use?

[Raimo33]

Which compiler did you use?

I used the option -DCMAKE_TOOLCHAIN_FILE=./cmake/arm-linux-gnueabihf.toolchain.cmake

C compiler ............................ GNU 13.3.0, /usr/bin/arm-linux-gnueabihf-gcc

[hebasto]

Which compiler did you use?

I used the option -DCMAKE_TOOLCHAIN_FILE=./cmake/arm-linux-gnueabihf.toolchain.cmake

C compiler ............................ GNU 13.3.0, /usr/bin/arm-linux-gnueabihf-gcc

This workflow is for cross-compiling. Did you try to build natively on your RPi?

[Raimo33]

Did you try to build natively on your RPi?

I get:

/home/pi/secp256k1/src/asm/field_10x26_arm.s:875: Error: selected processor does not support `ubfx r2,r3,#0,#22' in ARM mode
/home/pi/secp256k1/src/asm/field_10x26_arm.s:880: Error: selected processor does not support `movw r14,field_R1<<4' in ARM mode

when building natively on my RPI. the compiler is /usr/libexec/gcc/arm-linux-gnueabihf/14/
Apparently that's because RPIs build for armv6 architectures, not armv7...

and our field_10x26_arm.s is only compatible with armv7