https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105922
Bug ID: 105922
Summary: AArch64 SVE instruction generated with all SIMD lane
active and zero-divide exception flag raised
Product: gcc
Version: 12.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: kawakami.k at fujitsu dot com
Target Milestone: ---
Created attachment 53118
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53118&action=edit
preprocessed file
FDIV SVE instruction is generated with the predicate register whose all bits
are active. This FDIV sets the divide-by-zero flag (the bit 1 (DZC) of FPSR
register) unnecessarily. Should this instruction be executed with the
appropriate predicate bits?
In addition to FDIV, there may be other flags in the FPSR(IOC, OFC, UFC, IXC,
etc.) that could be set by performing operations on SIMD lanes that do not
contain the intended values in FADD/FSUB/FMUL as well.
/*
float a[7];
float b[7];
for(int i=0; i<7; i++) {
a[i] = some_initial\values;
}
for(int i=0; i<7; i++) {
b[i] = COEF / a[i];
}
*/
(p0 = {0x11, 0x11, 0x11, 0x1, 0x0, 0x0, 0x0, 0x0}
(p1 = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
(z1.s = {3, 3.29999995, 3.5999999, 3.9000001, 4.19999981, 4.5, 4.80000019, 0,
0, 0, 0, 0, 0, 0, 0, 0}
add x0, sp, 64
fdiv z0.s, p0/m, z0.s, z1.s # divide-by-zero exception raised
st1w z0.s, p1, [x0]
% gcc -v -save-temps -O3 -g -march=armv8.2-a+sve main.c
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/causal/gcc-12.1.0_gcc-11.3.0/libexec/gcc/aarch64-unknown-linux-gnu/12.1.0/lto-wrapper
Target: aarch64-unknown-linux-gnu
Configured with: ./configure --prefix=/opt/causal/gcc-12.1.0_gcc-11.3.0
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.1.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-g' '-march=armv8.2-a+sve'
'-mlittle-endian' '-mabi=lp64' '-dumpdir' 'a-'
/opt/causal/gcc-12.1.0_gcc-11.3.0/libexec/gcc/aarch64-unknown-linux-gnu/12.1.0/cc1
-E -quiet -v main.c -march=armv8.2-a+sve -mlittle-endian -mabi=lp64 -g
-fworking-directory -O3 -fpch-preprocess -o a-main.i
ignoring nonexistent directory
"/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/../../../../aarch64-unknown-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/include
/usr/local/include
/opt/causal/gcc-12.1.0_gcc-11.3.0/include
/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-g' '-march=armv8.2-a+sve'
'-mlittle-endian' '-mabi=lp64' '-dumpdir' 'a-'
/opt/causal/gcc-12.1.0_gcc-11.3.0/libexec/gcc/aarch64-unknown-linux-gnu/12.1.0/cc1
-fpreprocessed a-main.i -quiet -dumpdir a- -dumpbase main.c -dumpbase-ext .c
-march=armv8.2-a+sve -mlittle-endian -mabi=lp64 -g -O3 -version -o a-main.s
GNU C17 (GCC) version 12.1.0 (aarch64-unknown-linux-gnu)
compiled by GNU C version 12.1.0, GMP version 6.1.2, MPFR version
3.1.6-p2, MPC version 1.0.2, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C17 (GCC) version 12.1.0 (aarch64-unknown-linux-gnu)
compiled by GNU C version 12.1.0, GMP version 6.1.2, MPFR version
3.1.6-p2, MPC version 1.0.2, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 44e79a65ea64887de47cdc9a11ff4739
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-g' '-march=armv8.2-a+sve'
'-mlittle-endian' '-mabi=lp64' '-dumpdir' 'a-'
as -v --gdwarf-5 -EL -march=armv8.2-a+sve -mabi=lp64 -o a-main.o a-main.s
GNU assembler version 2.38 (aarch64-unknown-linux-gnu) using BFD version (GNU
Binutils) 2.38
COMPILER_PATH=/opt/causal/gcc-12.1.0_gcc-11.3.0/libexec/gcc/aarch64-unknown-linux-gnu/12.1.0/:/opt/causal/gcc-12.1.0_gcc-11.3.0/libexec/gcc/aarch64-unknown-linux-gnu/12.1.0/:/opt/causal/gcc-12.1.0_gcc-11.3.0/libexec/gcc/aarch64-unknown-linux-gnu/:/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/:/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/
LIBRARY_PATH=/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/:/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-g' '-march=armv8.2-a+sve'
'-mlittle-endian' '-mabi=lp64' '-dumpdir' 'a.'
/opt/causal/gcc-12.1.0_gcc-11.3.0/libexec/gcc/aarch64-unknown-linux-gnu/12.1.0/collect2
-plugin
/opt/causal/gcc-12.1.0_gcc-11.3.0/libexec/gcc/aarch64-unknown-linux-gnu/12.1.0/liblto_plugin.so
-plugin-opt=/opt/causal/gcc-12.1.0_gcc-11.3.0/libexec/gcc/aarch64-unknown-linux-gnu/12.1.0/lto-wrapper
-plugin-opt=-fresolution=a.res -plugin-opt=-pass-through=-lgcc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s
--eh-frame-hdr -dynamic-linker /lib/ld-linux-aarch64.so.1 -X -EL -maarch64linux
/lib/../lib64/crt1.o /lib/../lib64/crti.o
/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/crtbegin.o
-L/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0
-L/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/../../../../lib64
-L/lib/../lib64 -L/usr/lib/../lib64
-L/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/../../..
a-main.o -lgcc --push-state --as-needed -lgcc_s --pop-state -lc -lgcc
--push-state --as-needed -lgcc_s --pop-state
/opt/causal/gcc-12.1.0_gcc-11.3.0/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/crtend.o
/lib/../lib64/crtn.o
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-g' '-march=armv8.2-a+sve'
'-mlittle-endian' '-mabi=lp64' '-dumpdir' 'a.'
