https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92291
Bug ID: 92291
Summary: Non-optimal code generated for H8
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: mti-1 at tillenius dot com
Target Milestone: ---
I am using a cross compiler for Renesas H8S. In a few places it generates
really bad code. Given the following program:
struct s {
char a, b;
char c[11];
} x[2];
void test(int n)
{
struct s *sp = &x[n];
sp->a = 1;
sp->b = 1;
}
I would expect that the pointer "sp" is calculated once and reused to access
the fields "a" and "b". But instead the pointer is recalculated for each
access. This generates a lot of extra code, including calls to __mulhi3. I have
tested with gcc 8.2 and 9.2 and with different optimization levels (-O1, -O2,
-Os) all with the same result. With -O0 "sp" is only calculated once and kept
as a variable on the stack but the rest of the code is not as good as it could
be.
---
Using built-in specs.
COLLECT_GCC=h8300-none-elf-gcc
Target: h8300-none-elf
Configured with: /home/mti/abs/arm-none-eabi-gcc/h8/src/gcc-9.2.0/configure
--target=h8300-none-elf --prefix=/usr --with-native-system-header-dir=/include
--libexecdir=/usr/lib --enable-languages=c,c++ --enable-plugins
--disable-decimal-float --disable-libffi --disable-libgomp --disable-libmudflap
--disable-libquadmath --disable-libssp --disable-libstdcxx-pch
--disable-libstdcxx --disable-nls --disable-shared --disable-threads
--disable-tls --with-gnu-as --with-gnu-ld --with-system-zlib --without-headers
--with-python-dir=share/gcc-arm-none-eabi --with-gmp --with-mpfr --with-mpc
--with-isl --with-libelf --enable-gnu-indirect-function
--with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm'
--with-pkgversion='Arch Repository' --with-bugurl=https://bugs.archlinux.org/
--with-multilib-list=rmprofile
Thread model: single
gcc version 9.2.0 (Arch Repository)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-S' '-Wall'
/usr/lib/gcc/h8300-none-elf/9.2.0/cc1 -E -quiet -v test.c -Wall -O1
-fpch-preprocess -o test.i
ignoring nonexistent directory
"/usr/lib/gcc/h8300-none-elf/9.2.0/../../../../h8300-none-elf/sys-include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/h8300-none-elf/9.2.0/include
/usr/lib/gcc/h8300-none-elf/9.2.0/include-fixed
/usr/lib/gcc/h8300-none-elf/9.2.0/../../../../h8300-none-elf/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-S' '-Wall'
/usr/lib/gcc/h8300-none-elf/9.2.0/cc1 -fpreprocessed test.i -quiet -dumpbase
test.c -auxbase test -O1 -Wall -version -o test.s
GNU C17 (Arch Repository) version 9.2.0 (h8300-none-elf)
compiled by GNU C version 9.2.0, GMP version 6.1.2, MPFR version 4.0.2,
MPC version 1.1.0, isl version isl-0.19-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C17 (Arch Repository) version 9.2.0 (h8300-none-elf)
compiled by GNU C version 9.2.0, GMP version 6.1.2, MPFR version 4.0.2,
MPC version 1.1.0, isl version isl-0.19-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 67bb4ca8e2b97056926c3ecedb8a3eae
COMPILER_PATH=/usr/lib/gcc/h8300-none-elf/9.2.0/:/usr/lib/gcc/h8300-none-elf/9.2.0/:/usr/lib/gcc/h8300-none-elf/:/usr/lib/gcc/h8300-none-elf/9.2.0/:/usr/lib/gcc/h8300-none-elf/:/usr/lib/gcc/h8300-none-elf/9.2.0/../../../../h8300-none-elf/bin/
LIBRARY_PATH=/usr/lib/gcc/h8300-none-elf/9.2.0/:/usr/lib/gcc/h8300-none-elf/9.2.0/../../../../h8300-none-elf/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O1' '-S' '-Wall'
