https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90270
Bug ID: 90270
Summary: Do not select best induction variable optimization
Product: gcc
Version: 8.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rjiejie at me dot com
Target Milestone: ---
Using built-in specs.
COLLECT_GCC=/home/jojo/work/csky/cskytoolchain/csky-toolchain-build-riscv/riscv-install/bin/riscv64-unknown-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/home/jojo/work/csky/cskytoolchain/csky-toolchain-build-riscv/riscv-install/libexec/gcc/riscv64-unknown-linux-gnu/8.1.0/lto-wrapper
Target: riscv64-unknown-linux-gnu
Configured with:
/home/jojo/work/csky/cskytoolchain/csky-toolchain-build-riscv/riscv-gcc/configure
--target=riscv64-unknown-linux-gnu
--prefix=/home/jojo/work/csky/cskytoolchain/csky-toolchain-build-riscv/riscv-install
--with-sysroot=/home/jojo/work/csky/cskytoolchain/csky-toolchain-build-riscv/riscv-install/sysroot
--with-system-zlib --enable-shared --enable-tls --enable-languages=c,c++
--disable-libmudflap --disable-libssp --disable-libquadmath --disable-nls
--disable-bootstrap --src=.././riscv-gcc --enable-checking=yes
--with-pkgversion= --disable-multilib --with-abi=lp64 --with-arch=rv64imac
'CFLAGS_FOR_TARGET=-O2 -mcmodel=medlow' 'CXXFLAGS_FOR_TARGET=-O2
-mcmodel=medlow' CFLAGS='-O0 -g' CXXFLAGS='-O0 -g'
Thread model: posix
gcc version 8.1.0 ()
The following case do not select the best iv vars:
extern unsigned short int crcu32(unsigned int newval, unsigned short int crc);
unsigned short int func(unsigned short int crc)
{
unsigned int final_counts[8];
unsigned int track_counts[8];
unsigned int i;
for (i=0; i< 8; i++) {
crc=crcu32(final_counts[i],crc);
crc=crcu32(track_counts[i],crc);
}
return crc;
}
the asm code:
.L2:
slli s0,s1,2
add a5,sp,s0
lw a0,-4(a5)
addi s1,s1,1
call crcu32
addi a5,sp,32
add s0,a5,s0
mv a1,a0
lw a0,-4(s0)
call crcu32
mv a1,a0
bne s1,s2,.L2
i debug and found some info from "ivopts" tree optimization,
the bellow additional code will adjust cost of some type address in file
tree-ssa-loop-ivopts.c:
/* Cost of small invariant expression adjusted against loop niters
is usually zero, which makes it difficult to be differentiated
from candidate based on loop invariant variables. Secondly, the
generated invariant expression may not be hoisted out of loop by
following pass. We penalize the cost by rounding up in order to
neutralize such effects. */
cost.cost = adjust_setup_cost (data, cost.cost, true);
cost.scratch = cost.cost;
when i remove the two lines, the created asm code will better:
.L2:
lw a0,0(s0)
addi s0,s0,4
addi s1,s1,4
call crcu32
mv a1,a0
lw a0,-4(s1)
call crcu32
mv a1,a0
bne s0,s2,.L2
