https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105160
Bug ID: 105160
Summary: [12 regression] ipa modref marks functions with asm
volatile as const or pure
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: nsz at gcc dot gnu.org
CC: marxin at gcc dot gnu.org
Target Milestone: ---
the following code is miscompiled with gcc -O1
#define sysreg_read(regname) \
({ \
unsigned long __sr_val; \
asm volatile( \
"mrs %0, " #regname "\n" \
: "=r" (__sr_val)); \
\
__sr_val; \
})
#define sysreg_write(regname, __sw_val) \
do { \
asm volatile( \
"msr " #regname ", %0\n" \
: \
: "r" (__sw_val)); \
} while (0)
#define isb() \
do { \
asm volatile( \
"isb" \
: \
: \
: "memory"); \
} while (0)
static unsigned long sctlr_read(void)
{
return sysreg_read(sctlr_el1);
}
static void sctlr_write(unsigned long val)
{
sysreg_write(sctlr_el1, val);
}
static void sctlr_rmw(void)
{
unsigned long val;
val = sctlr_read();
val |= 1UL << 7;
sctlr_write(val);
}
void sctlr_read_multiple(void)
{
sctlr_read();
sctlr_read();
sctlr_read();
sctlr_read();
}
void sctlr_write_multiple(void)
{
sctlr_write(0);
sctlr_write(0);
sctlr_write(0);
sctlr_write(0);
sctlr_write(0);
}
void sctlr_rmw_multiple(void)
{
sctlr_rmw();
sctlr_rmw();
sctlr_rmw();
sctlr_rmw();
}
void function(void)
{
sctlr_read_multiple();
sctlr_write_multiple();
sctlr_rmw_multiple();
isb();
}
aarch64-linux-gnu-gcc -O1 compiles it to
(note 'function' and 'sctlr_rmw_multiple'):
sctlr_rmw:
mrs x0, sctlr_el1
orr x0, x0, 128
msr sctlr_el1, x0
ret
sctlr_read_multiple:
mrs x0, sctlr_el1
mrs x0, sctlr_el1
mrs x0, sctlr_el1
mrs x0, sctlr_el1
ret
sctlr_write_multiple:
mov x0, 0
msr sctlr_el1, x0
msr sctlr_el1, x0
msr sctlr_el1, x0
msr sctlr_el1, x0
msr sctlr_el1, x0
ret
sctlr_rmw_multiple:
ret
function:
isb
ret
a similar issue in linux (but lager source file) got bisected to
https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=1b62cddcf091fb8cadf575246a7d3ff778650a6b
commit 1b62cddcf091fb8cadf575246a7d3ff778650a6b
Author: Jan Hubicka <[email protected]>
Date: Fri Nov 12 14:00:47 2021 +0100
Fix ipa-modref pure/const discovery
PR ipa/103200
* ipa-modref.c (analyze_function, modref_propagate_in_scc): Do
not mark pure/const function if there are side-effects.
with -fdump-ipa-all
$ grep found t.c.087i.modref
Function found to be const: sctlr_rmw/2
Function found to be const: sctlr_read_multiple/3
Function found to be const: sctlr_write_multiple/4
Function found to be const: sctlr_rmw_multiple/5
even though t.c.086i.pure-const correctly identifies asm volatile
as not const/pure.
