[Bug 215977] clang on armv6 incorrectly emits call to sincos()

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=215977

            Bug ID: 215977
           Summary: clang on armv6 incorrectly emits call to sincos()
           Product: Base System
           Version: CURRENT
          Hardware: arm
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: arm
          Assignee: freebsd-arm at FreeBSD.org
          Reporter: jiashiun at gmail.com

Created attachment 178761
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=178761&action=edit
Example program to reproduce incorrect clang -fast-math behavior on armv6

Originally discussed on freebsd-arm@
https://lists.freebsd.org/pipermail/freebsd-arm/2017-January/015318.html

On armv6/12-current as of base r311687, clang command "cc -O1 -ffast-math"
optimizes adjacent calls to sin() and cos() to emits calls to nonexistent
function sincos(), resulting in linker error "undefined reference to `sincos'".

Example program sincos.c attached. 


% uname -a
FreeBSD rpi2 12.0-CURRENT FreeBSD 12.0-CURRENT #0 r311687: Tue Jan 10 21:36:16
CST 2017    
jsli at 4cbsd:/personal/freebsd/obj/x64/arm.armv6/personal/freebsd/fbsdsrc/sys/RPI2
 arm
% cc --version
FreeBSD clang version 3.9.1 (tags/RELEASE_391/final 289601) (based on LLVM
3.9.1)
Target: armv6--freebsd12.0-gnueabihf
Thread model: posix
InstalledDir: /usr/bin
% cc -O1 -ffast-math -lm sincos.c
/tmp/sincos-767f23.o: In function `main':
sincos.c:(.text+0x2c): undefined reference to `sincos'
cc: error: linker command failed with exit code 1 (use -v to see invocation)
% cc -O1 -fno-fast-math -lm sincos.c
% cc -O0 -ffast-math -lm sincos.c
%

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