https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118591
Bug ID: 118591
Summary: [lra][avr] Wrong code with -mlra in pr43879-3.c
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: gjl at gcc dot gnu.org
Target Milestone: ---
Created attachment 60227
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=60227&action=edit
pr43879-3.c: C test case from test suite
gcc.dg/torture/pr43879-3.c is failing with -mlra:
$ avr-gcc -mmcu=attiny40 -dumpbase "" -save-temps -dp -Os -o pr43879-3.elf
-mlra pr43879-3.c
Target: avr
Configured with: --target=avr --disable-nls --with-dwarf2 --with-gnu-as
--with-gnu-ld --with-long-double=64 --disable-libcc1 --disable-shared
--enable-languages=c,c++
gcc version 15.0.1 20250121 (experimental) (GCC)
The assembly reads:
main:
...
/* prologue: function */
/* frame size = 8 */
/* stack size = 8 */
.L__stack_usage = 8
# Y[5]:SI = 5 looks ok.
ldi r20,lo8(5) ; 173 [c=4 l=1] movqi_insn/1
subi r28,-5 ; 120 [c=8 l=2] *addhi3/3
sbci r29,-1
st Y+,r20 ; 169 [c=4 l=1] movqi_insn/2
st Y+,__zero_reg__ ; 177 [c=4 l=1] movqi_insn/2
st Y+,__zero_reg__ ; 178 [c=4 l=1] movqi_insn/2
st Y+,__zero_reg__ ; 179 [c=4 l=1] movqi_insn/2
subi r28,9 ; 122 [c=8 l=2] *addhi3/3
sbc r29,__zero_reg__
.L9:
# Y[1]:SI = 5 looks ok.
ldi r20,lo8(5) ; 180 [c=4 l=1] movqi_insn/1
ld __tmp_reg__,Y+ ; 73 [c=8 l=1] *addhi3/3
st Y+,r20 ; 143 [c=4 l=1] movqi_insn/2
st Y+,__zero_reg__ ; 184 [c=4 l=1] movqi_insn/2
st Y+,__zero_reg__ ; 185 [c=4 l=1] movqi_insn/2
st Y+,__zero_reg__ ; 186 [c=4 l=1] movqi_insn/2
subi r28,5 ; 75 [c=8 l=2] *addhi3/3
sbc r29,__zero_reg__
.L10:
# Reding 4 times R20:QI = Y[4] ???
subi r28,-4 ; 88 [c=8 l=2] *addhi3/3
sbci r29,-1
ld r20,Y ; 89 [c=4 l=1] movqi_insn/3
push r20 ; 11 [c=4 l=1] pushqi1/0
ld r20,Y ; 93 [c=4 l=1] movqi_insn/3
push r20 ; 13 [c=4 l=1] pushqi1/0
ld r20,Y ; 97 [c=4 l=1] movqi_insn/3
push r20 ; 15 [c=4 l=1] pushqi1/0
ld r20,Y ; 101 [c=4 l=1] movqi_insn/3
push r20 ; 17 [c=4 l=1] pushqi1/0
subi r28,-5 ; 132 [c=8 l=2] *addhi3/3
sbci r29,-1
# Reading from R22:SI = Y[9] but was never initialized. Note frame size is 8.
ld r22,Y+ ; 155 [c=4 l=1] movqi_insn/3
ld r23,Y+ ; 156 [c=4 l=1] movqi_insn/3
ld r24,Y+ ; 157 [c=4 l=1] movqi_insn/3
ld r25,Y+ ; 158 [c=4 l=1] movqi_insn/3
rcall f1 ; 19 [c=0 l=1] call_insn/1
The code after label .L10 looks very wrong. R23 (and maybe other regs) are
never properly initialized since they read garbage from the stack.
FYI, the error persists with -mno-fuse-add and is a bit more complicated then,
but the problem remains:
.L10:
subi r28,lo8(-(4)) ; 78 [c=4 l=5] movqi_insn/3
sbci r29,hi8(-(4))
ld r20,Y
subi r28,lo8((4))
sbci r29,hi8((4))
push r20 ; 11 [c=4 l=1] pushqi1/0
subi r28,lo8(-(4)) ; 79 [c=4 l=5] movqi_insn/3
sbci r29,hi8(-(4))
ld r20,Y
subi r28,lo8((4))
sbci r29,hi8((4))
push r20 ; 13 [c=4 l=1] pushqi1/0
subi r28,lo8(-(4)) ; 80 [c=4 l=5] movqi_insn/3
sbci r29,hi8(-(4))
ld r20,Y
subi r28,lo8((4))
sbci r29,hi8((4))
push r20 ; 15 [c=4 l=1] pushqi1/0
subi r28,lo8(-(4)) ; 81 [c=4 l=5] movqi_insn/3
sbci r29,hi8(-(4))
ld r20,Y
subi r28,lo8((4))
sbci r29,hi8((4))
push r20 ; 17 [c=4 l=1] pushqi1/0
subi r28,lo8(-(9)) ; 82 [c=16 l=8] *movsi/2
sbci r29,hi8(-(9))
ld r22,Y+
ld r23,Y+
ld r24,Y+
ld r25,Y
subi r28,lo8((9+3))
sbci r29,hi8((9+3))
Running the testsuite from $builddir/gcc:
$ make -k check-gcc RUNTESTFLAGS="--target_board=attiny40-sim
dg-torture.exp=pr43879-3.c -tool_opts='-mlra'"
...
FAIL: gcc.dg/torture/pr43879-3.c -O1 execution test
FAIL: gcc.dg/torture/pr43879-3.c -O2 execution test
FAIL: gcc.dg/torture/pr43879-3.c -O3 -fomit-frame-pointer -funroll-loops
-fpeel-loops -ftracer -finline-functions execution test
FAIL: gcc.dg/torture/pr43879-3.c -O3 -g execution test
FAIL: gcc.dg/torture/pr43879-3.c -Os execution test
FAIL: gcc.dg/torture/pr43879-3.c -O2 -flto -fno-use-linker-plugin
-flto-partition=none execution test
