Arm compilers have three floating point ABI options:
'soft' compiles floating point operations as function calls into a
software floating point library, which emulates floating point
operations using integer operations. Floating point function arguments
are passed using integer registers.
'softfp' also compiles floating point operations as function calls into
a floating point library and passes floating point function arguments
using integer registers, but the floating point library functions can
use FPU instructions if the CPU supports them.
'hard' compiles floating point operations into inline FPU instructions,
similarly to x86 and other architectures, and passes floating point
function arguments using FPU registers.
Not all AArch32 CPUs have FPUs or support Neon instructions, so on Linux
and Android platforms, the AArch32 SIMD dispatcher in libjpeg-turbo only
enables the Neon SIMD extensions at run time if /proc/cpuinfo indicates
that the CPU supports Neon instructions or if Neon instructions are
explicitly enabled (e.g. by passing -mfpu=neon to the compiler.) In
order to support all AArch32 CPUs using the same code base, i.e. to
support run-time FPU and Neon auto-detection, it is necessary to compile
the scalar C source code using -mfloat-abi=soft. However, the 'soft'
floating point ABI cannot be used when compiling Neon intrinsics, so the
intrinsics implementation of the Neon SIMD extensions must be compiled
using -mfloat-abi=softfp if the scalar C source code is compiled using
-mfloat-abi=soft.
This commit modifies the build system so that it detects whether
-mfloat-abi=softfp must be explicitly added to the compiler flags when
building the intrinsics implementation of the Neon SIMD extensions.
This will be necessary if the build is using the 'soft' floating
point ABI along with run-time auto-detection of Neon instructions.
Fixes#523
0081c2de20