https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114030
Bug ID: 114030
Summary: redundant load of inline function's arguments
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: absoler at smail dot nju.edu.cn
Target Milestone: ---
hi, here's the code. Redundant load will be introduced compiled with gcc-13.2.0
-O3.
```
// https://godbolt.org/z/3oGWq6anq
union U0 {
int f0;
long long f1;
int f2;
const unsigned char f3;
char f4;
};
union U2 {
char f0;
unsigned short f1;
unsigned short f2;
};
/* --- GLOBAL VARIABLES --- */
int g_3 = 0xD86E52D8L;
union U0 g_34 = {-1L};
union U2 g_35 = {0L};
int g_49 = 0xDC590CB2L;
int g_54[6][5] =
{{0L,0L,0L,0L,0L},{0x6833E1ABL,(-2L),0x6833E1ABL,(-2L),0x6833E1ABL},{0L,0L,0L,0L,0L},{0x6833E1ABL,(-2L),0x6833E1ABL,(-2L),0x6833E1ABL},{0L,0L,0L,0L,0L},{0x6833E1ABL,(-2L),0x6833E1ABL,(-2L),0x6833E1ABL}};
union U2 g_81 = {0L};
/* --- FORWARD DECLARATIONS --- */
static char(safe_rshift_func_int8_t_s_s)(char left, int right) { return
((left < 0) || (((int)right) < 0) || (((int)right) >= 32)) ? ((left))
: (left >> ((int)right));}
static unsigned char(safe_lshift_func_uint8_t_u_u)(unsigned char left, unsigned
int right) { return ((((unsigned int)right) >= 32) || (left >
((255) >> ((unsigned int)right)))) ? ((left)) :
(left << ((unsigned int)right));}
static char(safe_lshift_func_int8_t_s_s)(char left, int right) { return
((left < 0) || (((int)right) < 0) || (((int)right) >= 32) || (left >
((127) >> ((int)right)))) ? ((left)) : (left <<
((int)right));}
void func_1(void);
void func_31(union U0 p_32, union U2 p_33);
int func_42(union U0 p_43, int * p_44);
void func_1() {
func_31(g_34, g_35);
}
void func_31(union U0 g, union U2 h) {
int *i = &g_3;
g_34.f2 = 1;
*i = func_42((safe_rshift_func_int8_t_s_s(0, g.f4), g), &g_49);
}
int func_42(union U0 j, int *k) {
unsigned l_51 = 4294967295UL;
int *l = &g_3;
*l = g_54[4][0] |=
~safe_lshift_func_uint8_t_u_u(safe_lshift_func_int8_t_s_s((0x7BD129AC07F4C733LL
^ l_51), 6), j.f3);
return j.f0;
}
```
compiled binary is:
```
00000000004015b0 <func_1>:
func_1():
/root/myCSmith/test/output2.c:57
4015b0: movzbl 0x2b49(%rip),%ecx # 404100 <g_34> # not
necessary
4015b7: mov 0x2b43(%rip),%edx # 404100 <g_34>
safe_lshift_func_uint8_t_u_u():
/root/myCSmith/test/output2.c:62
4015bd: mov $0xffffff33,%eax
func_31():
/root/myCSmith/test/output2.c:62
4015c2: movl $0x1,0x2b34(%rip) # 404100 <g_34>
safe_lshift_func_uint8_t_u_u():
/root/myCSmith/test/output2.c:49
4015cc: cmp $0x1f,%cl
4015cf: ja 4015ec <func_1+0x3c>
/root/myCSmith/test/output2.c:49 (discriminator 1)
4015d1: mov $0xff,%esi
4015d6: sar %cl,%esi
4015d8: cmp $0xcb,%esi
4015de: jle 4015ec <func_1+0x3c>
/root/myCSmith/test/output2.c:49 (discriminator 3)
4015e0: mov $0xcc,%eax
4015e5: shl %cl,%eax
func_42():
/root/myCSmith/test/output2.c:69 (discriminator 2)
4015e7: movzbl %al,%eax
4015ea: not %eax
/root/myCSmith/test/output2.c:68
4015ec: or %eax,0x2ade(%rip) # 4040d0 <g_54+0x50>
func_31():
/root/myCSmith/test/output2.c:63 (discriminator 2)
4015f2: mov %edx,0x2b10(%rip) # 404108 <g_3>
func_1():
/root/myCSmith/test/output2.c:58
4015f8: retq
4015f9: nopl 0x0(%rax)
```
the load at address 0x4015b0 is redundant.
This behavior is regression with gcc-13.2.0 and a necessary flag -O3, and can
be triggered with gcc-8.2.0 with -O2 flag.
if compiled with gcc-13.2.0 -O2, there won't be such a load operation.
