https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113032
Bug ID: 113032
Summary: RISCV linker relaxation leaves redundant addi (from
load immediate)
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: iwfinlay at gmail dot com
Target Milestone: ---
Created attachment 56887
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56887&action=edit
Source files and save-temps for ELF build
In the ELF image for RISCV 32-bit, the lower 12-bit parts of a load immediate
are zero but not removed. Hence, it appears as a 'mv' in the objdump of the
program ELF.
20010064 <_Z6globalv>:
20010064: 80000537 lui a0,0x80000
20010068: 00050513 mv a0,a0 <-- (1)
2001006c: 00008067 ret
20010070 <_Z4initv>:
20010070: 800007b7 lui a5,0x80000
20010074: 00078793 mv a5,a5 <-- (2)
20010078: 3e700713 li a4,999
2001007c: 00e7a223 sw a4,4(a5) # 80000004
<__global_pointer$+0xfffff804>
20010080: 0ea00713 li a4,234
20010084: 00e7a423 sw a4,8(a5)
20010088: 00008067 ret
2001008c <_Z5pcnt0v>:
2001008c: 800007b7 lui a5,0x80000
20010090: 00078793 mv a5,a5 <-- (3)
20010094: 0047a703 lw a4,4(a5) # 80000004
<__global_pointer$+0xfffff804>
20010098: 60271713 cpop a4,a4
The command line is:
riscv64-unknown-elf-g++ --save-temps -march=rv32imv_zbb_zbs -mabi=ilp32 -O3
-Wall -Wextra -o relax.elf main.cpp test.cpp startup.cpp -fno-builtin -static
-fno-common -mcmodel=medlow -nostdlib -T link.ld
The behavior is the same if I drop -fno-builtin -fno-common -mcmodel (just need
to provide memset).
I'm attaching a tar-file for the above.
I reviewed 91713 but concluded that it's different. I also filed yesterday. I
apologize for wasting reviewer time. It's the same test case but I'm now
including the main to show overall optimization.
Thanks for the previous feedback.
