https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112413
Bug ID: 112413
Summary: Wrong switch jump table offset
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent.riviere at freesbee dot fr
Target Milestone: ---
In some circumstances, gcc produces bad code for switch instruction.
Main goal of the testcase is to force gcc to produce a jump table.
$ cat swi.c
int g;
void f(int i)
{
switch (i)
{
case 0: g = 6082; break;
case 1: g = 9332; break;
case 2: g = 5642; break;
case 3: g = 1423; break;
case 4: g = 2152; break;
case 5: g = 6779; break;
case 6: g = 7074; break;
case 7: g = 8280; break;
}
}
$ m68k-linux-gcc -Os -S -o - swi.c -mlong-jump-table-offsets -malign-int
#NO_APP
.file "swi.c"
.text
.align 2
.globl f
.type f, @function
f:
move.l 4(%sp),%d0
moveq #7,%d1
cmp.l %d0,%d1
jcs .L1
lsl.l #2,%d0
move.l .L4(%pc,%d0.l),%d0
jmp %pc@(2,%d0:l)
.balignw 4,0x284c |Potential bug here
.L4:
.long .L11-.L4
.long .L10-.L4
.long .L9-.L4
.long .L8-.L4
.long .L7-.L4
.long .L6-.L4
.long .L5-.L4
.long .L3-.L4
.L11:
move.l #6082,g
.L1:
rts
.L10:
move.l #9332,g
jra .L1
...
As the jmp may not be aligned on a multiple of 4, the .balignw directive may
introduce a 2-byte filler, causing jmp to use a wrong offset.
Same happens with m68k-elf-gcc.
