[all-commits] [llvm/llvm-project] a62962: [libc][math] Improve atanf performance. (#85463)

[lntue via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a629621454838207ca49bcfd773d5aa0671659f1
      https://github.com/llvm/llvm-project/commit/a629621454838207ca49bcfd773d5aa0671659f1
  Author: lntue <35648136+lntue at users.noreply.github.com>
  Date:   2024-03-18 (Mon, 18 Mar 2024)

  Changed paths:
    M libc/src/math/generic/CMakeLists.txt
    M libc/src/math/generic/atanf.cpp
    M libc/src/math/generic/inv_trigf_utils.cpp
    M libc/src/math/generic/inv_trigf_utils.h
    M libc/test/src/math/CMakeLists.txt
    M libc/test/src/math/atanf_test.cpp
    M libc/test/src/math/exhaustive/atanf_test.cpp
    R libc/test/src/math/inv_trigf_utils_test.cpp
    M utils/bazel/llvm-project-overlay/libc/BUILD.bazel

  Log Message:
  -----------
  [libc][math] Improve atanf performance. (#85463)

Simplify the range reduction logic and computations. Performance test
using `perf.sh` from CORE-MATH project on Ryzen 5900X:

Before:
```
$ ./perf.sh atanf --rdtsc --path1
LIBC-location: /home/lnt/experiment/llvm-project/build/projects/libc/lib/libllvmlibc.a
GNU libc version: 2.35
GNU libc release: stable
-- CORE-MATH reciprocal throughput --
[####################] 100 %
Ntrial = 20 ; Min = 14.369 + 0.556 clc/call; Median-Min = 0.613 clc/call; Max = 15.061 clc/call;
-- System LIBC reciprocal throughput --
[####################] 100 %
Ntrial = 20 ; Min = 26.180 + 0.015 clc/call; Median-Min = 0.014 clc/call; Max = 26.260 clc/call;
-- LIBC reciprocal throughput --
[####################] 100 %
Ntrial = 20 ; Min = 21.237 + 0.022 clc/call; Median-Min = 0.020 clc/call; Max = 21.272 clc/call;

$ ./perf.sh atanf --rdtsc --path1 --latency
LIBC-location: /home/lnt/experiment/llvm-project/build/projects/libc/lib/libllvmlibc.a
GNU libc version: 2.35
GNU libc release: stable
-- CORE-MATH latency --
[####################] 100 %
Ntrial = 20 ; Min = 50.505 + 0.045 clc/call; Median-Min = 0.037 clc/call; Max = 50.579 clc/call;
-- System LIBC latency --
[####################] 100 %
Ntrial = 20 ; Min = 62.438 + 0.836 clc/call; Median-Min = 0.049 clc/call; Max = 64.498 clc/call;
-- LIBC latency --
[####################] 100 %
Ntrial = 20 ; Min = 67.781 + 0.546 clc/call; Median-Min = 0.028 clc/call; Max = 68.844 clc/call;
```

After:
```
$ ./perf.sh atanf --rdtsc --path2
LIBC-location: /home/lnt/experiment/llvm/llvm-project/build/projects/libc/lib/libllvmlibc.a
GNU libc version: 2.35
GNU libc release: stable
-- CORE-MATH reciprocal throughput --
[####################] 100 %
Ntrial = 20 ; Min = 14.400 + 0.353 clc/call; Median-Min = 0.404 clc/call; Max = 14.863 clc/call;
-- System LIBC reciprocal throughput --
[####################] 100 %
Ntrial = 20 ; Min = 25.247 + 0.783 clc/call; Median-Min = 0.714 clc/call; Max = 26.238 clc/call;
-- LIBC reciprocal throughput --
[####################] 100 %
Ntrial = 20 ; Min = 13.751 + 0.158 clc/call; Median-Min = 0.140 clc/call; Max = 14.006 clc/call;

$ ./perf.sh atanf --rdtsc --path2 --latency
LIBC-location: /home/lnt/experiment/llvm/llvm-project/build/projects/libc/lib/libllvmlibc.a
GNU libc version: 2.35
GNU libc release: stable
-- CORE-MATH latency --
[####################] 100 %
Ntrial = 20 ; Min = 51.837 + 0.073 clc/call; Median-Min = 0.058 clc/call; Max = 52.000 clc/call;
-- System LIBC latency --
[####################] 100 %
Ntrial = 20 ; Min = 62.487 + 1.878 clc/call; Median-Min = 1.965 clc/call; Max = 64.569 clc/call;
OK
-- LIBC latency --
[####################] 100 %
Ntrial = 20 ; Min = 55.414 + 1.312 clc/call; Median-Min = 0.345 clc/call; Max = 58.362 clc/call;
```



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