On Tue, Oct 9, 2012 at 11:37 PM, Matthew Gretton-Dann
<matthew.gretton-dann@linaro.org> wrote:
>> >> /* arm-none-linux-gnueabi-gcc -mcpu=cortex-a15 -mfpu=vfpv4 -S -o-
>> >> /tmp/fma.c -mfloat-abi=hard -O2 */
>> >> float f(float a, float b, float c)
>> >> {
>> >> return a * b + c;
>> >> }
>> >> /* end of tmp.c */
>> >>
>> >> (Note that -mfloat-abi=softfp will also work in this example. Which
>> >> one you want to use depends on whether you have configured your system
>> >> for hard or soft-float ABIs).
>> >>
>> > I checked both with -mfpu=vfpv3 and -mfpu=vfpv4 and it generates the
>> > same
>> > assembly code. VMLA insn is emitted for both the cases. I was wondering
>> > if I
>> > can get any test case so that I may observe the difference in the two
>> > objdumps.
>>
>> Which compiler are you using? VFMA support is only in trunk FSF GCC.
>> Linaro has not yet backported support to 4.7.
>
>
> I am using FSF GCC only.
What version of GCC (what does arm-none-linux-gneabi-gcc -v report?).
# arm-none-linux-gneabi-gcc -v
Using built-in specs.
COLLECT_GCC=arm-none-linux-gneabi-gcc
COLLECT_LTO_WRAPPER=/opt/toolchains/arm/bin/../libexec/gcc/arm-none-linux-gneabi/4.6.3/lto-wrapper
Target: arm-none-linux-gneabi
Configured with: /home/user/arm-src/build/sources/gcc_1/configure --build=i686-pc-linux-gnu --host=i686-pc-linux-gnu --target=arm-none-linux-gneabi --prefix=/opt/arm --with-sysroot=/opt/arm/arm-none-linux-gneabi/sys-root --disable-libmudflap --disable-libssp --disable-libgomp --disable-nls --disable-libstdcxx-pch --with-interwork --with-mode=arm --with-fpu=vfp3 --with-cpu=cortex-a9 --with-tune=cortex-a9 --with-float=softfp --enable-extra-vd-multilibs --enable-poison-system-directories --enable-long-long --enable-threads --enable-languages=c,c++ --enable-shared --enable-lto --enable-symvers=gnu --enable-__cxa_atexit --with-pkgversion=arm-toolchain.v1 --with-gnu-as --with-gnu-ld --with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm' --with-build-time-tools=/opt/arm/bin --with-gmp=/opt/arm --with-mpfr=/opt/arm --with-ppl=/opt/arm --with-cloog=/opt/arm --with-libelf=/opt/arm
Thread model: posix
gcc version 4.6.3 (arm-toolchain.v1)
When I compile the test case above with a recent (within last month or
so) trunk GCC I get the following output which uses vfma:
$ /work/builds/gcc-fsf-arm-none-linux-gnueabi/tools/bin/arm-none-linux-gnueabi-gcc
-mcpu=cortex-a15 -mfpu=vfpv4 -S -o- /tmp/fma.c -mfloat-abi=hard -O2
.cpu cortex-a15
.eabi_attribute 27, 3
.eabi_attribute 28, 1
.fpu vfpv4
.eabi_attribute 20, 1
.eabi_attribute 21, 1
.eabi_attribute 23, 3
.eabi_attribute 24, 1
.eabi_attribute 25, 1
.eabi_attribute 26, 2
.eabi_attribute 30, 2
.eabi_attribute 34, 1
.eabi_attribute 18, 4
.file "fma.c"
.text
.align 2
.global f
.type f, %function
f:
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
vfma.f32 s2, s0, s1
fcpys s0, s2
bx lr
.size f, .-f
.ident "GCC: (GNU) 4.8.0 20120913 (experimental)"
.section .note.GNU-stack,"",%progbits
$ arm-none-linux-gnueabi-gcc -mcpu=cortex-a15 -mfpu=vfpv4 -S -o- prog.c -O2
.cpu cortex-a15
.eabi_attribute 27, 3
.fpu vfpv4
.eabi_attribute 20, 1
.eabi_attribute 21, 1
.eabi_attribute 23, 3
.eabi_attribute 24, 1
.eabi_attribute 25, 1
.eabi_attribute 26, 2
.eabi_attribute 30, 2
.eabi_attribute 34, 0
.eabi_attribute 18, 4
.file "prog.c"
.section .text.f,"ax",%progbits
.align 2
.global f
.type f, %function
f:
.fnstart
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
fmsr s14, r0
fmsr s13, r2
fmsr s15, r1
fmacs s13, s14, s15
fmrs r0, s13
bx lr
.fnend
.size f, .-f
.section .text.startup.main,"ax",%progbits
.align 2
.global main
.type main, %function
main:
.fnstart
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
bx lr
.fnend
.size main, .-main
.ident "GCC: (VDLinux.GA1.2012-10-03) 4.6.4"
.section .note.GNU-stack,"",%progbits
I could not conclude the difference in two results and the overall conclusion for my query... Can you please guide to dig deeper in it?
Jubi