http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51980
Bug #: 51980
Summary: ARM - Neon code polluted by useless stores to the
stack with vuzpq / vzipq / vtrnq
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: eric.ba...@allegorithmic.com
Created attachment 26442
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26442
Minimal repro case (C file)
When using UZP/ZIP/TRN Neon intrinsics, gcc-trunk generates a whole lot of
stack operations (and associated stack alignment operations) even if everything
can purely be done using Neon registers.
Compiler used is GCC trunk, rev 183468, compiled with Android's build-gcc.sh
(arm-linux-androideabi).
Command line is:
arm-linux-androideabi-g++ -c -march=armv7-a -mcpu=cortex-a9 -mfloat-abi=hard
-mfpu=vfp -flax-vector-conversions -mfpu=neon -O2 -o test.s test.c -S
Generated assembly code for attached C file is:
_Z13sqrlen4D_16u817__simd128_uint8_tS_:
vabd.u8 q1, q0, q1
stmfd sp!, {r4, fp} <= Unnecessary
add fp, sp, #4 <= Unnecessary
sub sp, sp, #48 <= Unnecessary
add r3, sp, #15 <= Unnecessary
vmull.u8 q0, d2, d2
bic r3, r3, #15 <= Unnecessary
vmull.u8 q8, d3, d3
vuzp.32 q0, q8
vstmia r3, {d0-d1} <= Unnecessary, caused by vuzp.32
vstr d16, [r3, #16] <= Unnecessary, caused by vuzp.32
vstr d17, [r3, #24] <= Unnecessary, caused by vuzp.32
vpaddl.u16 q0, q0
vpadal.u16 q0, q8
sub sp, fp, #4 <= Unnecessary
ldmfd sp!, {r4, fp} <= Unnecessary
bx lr
As no stack operation is needed in this function, ideally the following should
be generated instead:
_Z13sqrlen4D_16u817__simd128_uint8_tS_:
vabd.u8 q1, q0, q1
vmull.u8 q0, d2, d2
vmull.u8 q8, d3, d3
vuzp.32 q0, q8
vpaddl.u16 q0, q0
vpadal.u16 q0, q8
bx lr
This makes even tight Neon functions written with intrinsics much larger and
slower than necessary, and makes it very hard to write performance-oriented
code with intrinsics in arm-gcc.
gcc -v yields:
Using built-in specs.
COLLECT_GCC=/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/bin/arm-linux-androideabi-g++
COLLECT_LTO_WRAPPER=/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/libexec/gcc/arm-linux-androideabi/4.7.0/lto-wrapper
Target: arm-linux-androideabi
Configured with: /home/eb/android-ndk-r6/src/build/../gcc/gcc-4.7.0/configure
--prefix=/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86
--target=arm-linux-androideabi --host=i386-linux-gnu --build=i386-linux-gnu
--with-gnu-as --with-gnu-ld --enable-languages=c,c++
--with-gmp=/tmp/ndk-eb/build/toolchain/temp-install
--with-mpfr=/tmp/ndk-eb/build/toolchain/temp-install
--with-mpc=/tmp/ndk-eb/build/toolchain/temp-install --disable-libssp
--enable-threads --disable-nls --disable-libmudflap --disable-libgomp
--disable-libstdc__-v3 --disable-sjlj-exceptions --disable-shared --disable-tls
--with-float=soft --with-fpu=vfp --with-arch=armv5te --enable-target-optspace
--enable-initfini-array --disable-nls
--prefix=/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86
--with-sysroot=/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/sysroot
--with-binutils-version=2.21.53 --with-mpfr-version=3.0.1
--with-gmp-version=5.0.2 --with-gcc-version=4.7.0 --with-gdb-version=6.6
--with-mpc-version=0.9 --with-arch=armv5te --enable-libstdc__-v3
--program-transform-name='s,^,arm-linux-androideabi-,'
Thread model: posix
gcc version 4.7.0 20120124 (experimental) (GCC)
COLLECT_GCC_OPTIONS='-c' '-march=armv7-a' '-mcpu=cortex-a9' '-mfloat-abi=hard'
'-mfpu=vfp' '-flax-vector-conversions' '-mfpu=neon' '-O2' '-o' 'test.s' '-S'
'-v' '-mtls-dialect=gnu'
/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/libexec/gcc/arm-linux-androideabi/4.7.0/cc1plus
-quiet -v -imultilib armv7-a -D_GNU_SOURCE test.c -mbionic -fPIC -quiet
-dumpbase test.c -march=armv7-a -mcpu=cortex-a9 -mfloat-abi=hard -mfpu=vfp
-mfpu=neon -mtls-dialect=gnu -auxbase-strip test.s -O2 -version
-flax-vector-conversions -o test.s -fno-exceptions -fno-rtti
GNU C++ (GCC) version 4.7.0 20120124 (experimental) (arm-linux-androideabi)
compiled by GNU C version 4.6.0 20110603 (Red Hat 4.6.0-10), GMP version
5.0.2, MPFR version 3.0.1, MPC version 0.9
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
ignoring nonexistent directory
"/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/../../../../arm-linux-androideabi/include/c++/4.7.0"
ignoring nonexistent directory
"/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/../../../../arm-linux-androideabi/include/c++/4.7.0/arm-linux-androideabi/armv7-a"
ignoring nonexistent directory
"/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/../../../../arm-linux-androideabi/include/c++/4.7.0/backward"
ignoring nonexistent directory
"/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/sysroot/usr/local/include"
#include "..." search starts here:
#include <...> search starts here:
/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/include
/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/include-fixed
/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/../../../../arm-linux-androideabi/include
/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/sysroot/usr/include
End of search list.
GNU C++ (GCC) version 4.7.0 20120124 (experimental) (arm-linux-androideabi)
compiled by GNU C version 4.6.0 20110603 (Red Hat 4.6.0-10), GMP version
5.0.2, MPFR version 3.0.1, MPC version 0.9
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: d84173bb26a7319ac9d4c1278a6a7e04
COMPILER_PATH=/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/libexec/gcc/arm-linux-androideabi/4.7.0/:/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/libexec/gcc/arm-linux-androideabi/4.7.0/:/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/libexec/gcc/arm-linux-androideabi/:/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/:/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/:/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/../../../../arm-linux-androideabi/bin/
LIBRARY_PATH=/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/armv7-a/:/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/../../../../arm-linux-androideabi/lib/armv7-a/:/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/:/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/lib/gcc/arm-linux-androideabi/4.7.0/../../../../arm-linux-androideabi/lib/:/home/eb/android-ndk-r6/toolchains/arm-linux-androideabi-4.7.0/prebuilt/linux-x86/sysroot/usr/lib/
COLLECT_GCC_OPTIONS='-c' '-march=armv7-a' '-mcpu=cortex-a9' '-mfloat-abi=hard'
'-mfpu=vfp' '-flax-vector-conversions' '-mfpu=neon' '-O2' '-o' 'test.s' '-S'
'-v' '-mtls-dialect=gnu'
