improve performance of powermod for bitintegers#9
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Use an atomic fetch and add to fix a data race in `Module()` identified by tsan: ``` ./usr/bin/julia -t4,0 --gcthreads=1 -e 'Threads.@threads for i=1:100 Module() end' ================== WARNING: ThreadSanitizer: data race (pid=5575) Write of size 4 at 0xffff9bf9bd28 by thread T9: #0 jl_new_module__ /home/user/c/julia/src/module.c:487:22 (libjulia-internal.so.1.13+0x897d4) #1 jl_new_module_ /home/user/c/julia/src/module.c:527:22 (libjulia-internal.so.1.13+0x897d4) #2 jl_f_new_module /home/user/c/julia/src/module.c:649:22 (libjulia-internal.so.1.13+0x8a968) #3 <null> <null> (0xffff76a21164) #4 <null> <null> (0xffff76a1f074) #5 <null> <null> (0xffff76a1f0c4) #6 _jl_invoke /home/user/c/julia/src/gf.c (libjulia-internal.so.1.13+0x5ea04) #7 ijl_apply_generic /home/user/c/julia/src/gf.c:3892:12 (libjulia-internal.so.1.13+0x5ea04) #8 jl_apply /home/user/c/julia/src/julia.h:2343:12 (libjulia-internal.so.1.13+0x9e4c4) #9 start_task /home/user/c/julia/src/task.c:1249:19 (libjulia-internal.so.1.13+0x9e4c4) Previous write of size 4 at 0xffff9bf9bd28 by thread T10: #0 jl_new_module__ /home/user/c/julia/src/module.c:487:22 (libjulia-internal.so.1.13+0x897d4) #1 jl_new_module_ /home/user/c/julia/src/module.c:527:22 (libjulia-internal.so.1.13+0x897d4) #2 jl_f_new_module /home/user/c/julia/src/module.c:649:22 (libjulia-internal.so.1.13+0x8a968) #3 <null> <null> (0xffff76a21164) #4 <null> <null> (0xffff76a1f074) #5 <null> <null> (0xffff76a1f0c4) #6 _jl_invoke /home/user/c/julia/src/gf.c (libjulia-internal.so.1.13+0x5ea04) #7 ijl_apply_generic /home/user/c/julia/src/gf.c:3892:12 (libjulia-internal.so.1.13+0x5ea04) #8 jl_apply /home/user/c/julia/src/julia.h:2343:12 (libjulia-internal.so.1.13+0x9e4c4) #9 start_task /home/user/c/julia/src/task.c:1249:19 (libjulia-internal.so.1.13+0x9e4c4) Location is global 'jl_new_module__.mcounter' of size 4 at 0xffff9bf9bd28 (libjulia-internal.so.1.13+0x3dbd28) ``` (cherry picked from commit 9039555)
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compared to 54866 this:
iszero(r)inmod(a, ::SignedMultiplicativeInverse)for cases likemod(0, multiplicativeinverse(-5))x, mthat were failing(p > 2sizeof(mm))so we don't bother computing the mi when the power is very small