https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114173
Bug ID: 114173
Summary: miss optimization of redundant load operation, may
confused by type conversion
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: absoler at smail dot nju.edu.cn
Target Milestone: ---
Hi, here's the code:
```
typedef signed char int8_t;
typedef unsigned char uint8_t;
typedef signed short int int16_t;
typedef unsigned short int uint16_t;
typedef signed int int32_t;
typedef unsigned int uint32_t;
typedef signed long int int64_t;
typedef unsigned long int uint64_t;
/* --- Struct/Union Declarations --- */
struct S1 {
uint32_t f0;
int32_t f1;
uint16_t f2;
};
/* --- GLOBAL VARIABLES --- */
int32_t g_6 = 0xA0CEC519L;
int32_t g_63[10] =
{0x62155B98L,0xEEA2DBBAL,0xEEA2DBBAL,0x62155B98L,0xEEA2DBBAL,0xEEA2DBBAL,0x62155B98L,0xEEA2DBBAL,0xEEA2DBBAL,0x62155B98L};
struct S1 g_304 =
{0x917144CEL,-8L,0x6D84L,-2L,0xD005B892436443A6LL,0xF5L,0x7EDC5F4166794133LL};
/* --- FORWARD DECLARATIONS --- */
void func_1() {
int32_t b = 1;
int32_t c;
int8_t d;
if (d = c = (uint16_t)((uint8_t)g_63[4] + b) - b) {
uint16_t *e = &g_304.f0;
*e = c;
}
}
```
compiled with gcc-13.2.0 -O3, generated binary is:
https://godbolt.org/z/P9scnWqsa
```
00000000004015f0 <func_1>:
func_1():
/root/loadtest3/test/output2.c:43
4015f0: cmpb $0x0,0x2ab9(%rip) # 4040b0 <g_63+0x10>
4015f7: movzbl 0x2ab2(%rip),%eax # 4040b0 <g_63+0x10>
4015fe: je 401607 <func_1+0x17>
/root/loadtest3/test/output2.c:45
401600: mov %ax,0x2a79(%rip) # 404080 <g_304>
/root/loadtest3/test/output2.c:47
401607: retq
401608: nopl 0x0(%rax,%rax,1)
```
the compare and load instructions can swap and $eax can be used in the compare,
instead of a memory access
