https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107415
Bug ID: 107415
Summary: RISCV-gcc: Leaf function compiles as recursive with
-O3
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: michael.meier at hexagon dot com
Target Milestone: ---
Created attachment 53776
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53776&action=edit
The -save-temps output as requested
I am using gcc 12.1.0 to compile for RISC-V. Compiling the following leaf
function (it's in the .i file in the attachment) results in gcc generating a
recursive call to memset itself, resulting in an endless loop. The code is a
slightly reduced version function that led me to finding this issue. It does
not make sense as memset, but it triggers the issue.
void* memset(void* dest, int byte, size_t len)
{
if uintptr_t)dest | len) & (sizeof(uintptr_t)-1)) == 0) {
uintptr_t *d = dest;
*d = byte;
} else {
char *d = dest;
while (d < (char*)(dest + len))
*d++ = byte;
}
return dest;
}
First lines of the objdump output of the generated object file:
:
0: ff010113addisp,sp,-16
4: 00812423sw s0,8(sp)
8: 00912223sw s1,4(sp)
c: 00112623sw ra,12(sp)
10: 01010413addis0,sp,16
14: 00c56733or a4,a0,a2
18: 00377713andia4,a4,3
1c: 00050493mv s1,a0
20: 02070a63beqza4,54 <.L2>
20: R_RISCV_BRANCH .L2
0024 <.LBB2>:
24: 00c507b3add a5,a0,a2
28: 00f57a63bgeua0,a5,3c <.L4>
28: R_RISCV_BRANCH .L4
2c: 01859593sllia1,a1,0x18
0030 <.LVL2>:
30: 4185d593sraia1,a1,0x18
34: 0097auipc ra,0x0
34: R_RISCV_CALLmemset
34: R_RISCV_RELAX *ABS*
38: 80e7jalrra # 34 <.LVL2+0x4>
At address 38 inside we find a call to memset. This instruction can be jumped
over if the right conditions on a4 and a0 happen to be true. However running
the function up to the jalr memset does not change any of these conditions.
After calling memset, the PC will arrive will arrive at the jalr memset again,
resulting in an endless loop.
Output of gcc -v:
Using built-in specs.
COLLECT_GCC=/home/memi/Downloads/riscv/bin/riscv64-unknown-elf-gcc
COLLECT_LTO_WRAPPER=/home/memi/Downloads/riscv/bin/../libexec/gcc/riscv64-unknown-elf/12.1.0/lto-wrapper
Target: riscv64-unknown-elf
Configured with: /tmp/rv_gcc/riscv-gnu-toolchain/gcc/configure
--target=riscv64-unknown-elf --prefix=/opt/riscv --disable-shared
--disable-threads --enable-languages=c,c++ --with-pkgversion=g1ea978e3066
--with-system-zlib --enable-tls --with-newlib
--with-sysroot=/opt/riscv/riscv64-unknown-elf
--with-native-system-header-dir=/include --disable-libmudflap --disable-libssp
--disable-libquadmath --disable-libgomp --disable-nls
--disable-tm-clone-registry --src=/tmp/rv_gcc/riscv-gnu-toolchain/gcc
--enable-multilib
--with-multilib-generator='rv32i-ilp32--;rv32ic-ilp32--;rv32im-ilp32--;rv32imc-ilp32--'
--with-abi=lp64d --with-arch=rv64imafdc --with-tune=rocket --with-isa-spec=2.2
'CFLAGS_FOR_TARGET=-Os -mcmodel=medlow' 'CXXFLAGS_FOR_TARGET=-Os
-mcmodel=medlow'
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 12.1.0 (g1ea978e3066)
Complete command line that triggers the problem:
/home/memi/Downloads/riscv/bin/riscv64-unknown-elf-gcc -c own-memset.c -O3
-DNDEBUG -march=rv32im -mabi=ilp32 -msmall-data-limit=8 -mno-save-restore
-fmessage-length=0 -fsigned-char -ffunction-sections -fdata-sections -g
-fno-omit-frame-pointer -std=gnu11 -MD -MT
softconsole_oriole_main/CMakeFiles/MIV_Project.dir/ISP_PRO.c.obj -save-temps
The compiler output (on the console):
None
The preprocessed file is attached.
