[PATCH] D49514: [compiler-rt] [builtins] Add logb/logbf/logbl methods to compiler-rt to avoid libm dependencies when possible.

[Jordan Rupprecht via Phabricator via llvm-commits]

rupprecht created this revision.
rupprecht added reviewers: saugustine, efriedma.
Herald added subscribers: Sanitizers, llvm-commits, delcypher, kbarton, mgorny, dberris, nemanjai.

The complex division builtins (div?c3) use logb methods from libm to scale numbers during division and avoid rounding issues. However, these come from libm, meaning anyone that uses --rtlib=compiler-rt also has to include -lm. Implement logb* methods for standard ieee 754 floats so we can avoid -lm on those platforms, falling back to the old behavior (using either logb() or __builtin_logb()) when not supported.

These new methods are defined internally as __compiler_rt_logb* so as not to conflict with the libm definitions in any way.

Fixes PR32279 and PR28652.

Note: this is proposed as an alternative to just adding -lm: https://reviews.llvm.org/D49330.


Repository:
  rCRT Compiler Runtime

https://reviews.llvm.org/D49514

Files:
  lib/builtins/CMakeLists.txt
  lib/builtins/compiler_rt_logb.c
  lib/builtins/compiler_rt_logbf.c
  lib/builtins/compiler_rt_logbl.c
  lib/builtins/divdc3.c
  lib/builtins/divsc3.c
  lib/builtins/divtc3.c
  lib/builtins/divxc3.c
  lib/builtins/fp_lib.h
  lib/builtins/fp_logb_impl.inc
  lib/builtins/int_math.h
  lib/builtins/ppc/divtc3.c
  test/builtins/Unit/compiler_rt_logb_test.c
  test/builtins/Unit/compiler_rt_logbf_test.c
  test/builtins/Unit/compiler_rt_logbl_test.c

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