https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109416
Bug ID: 109416
Summary: Missed constant propagation cases after reload
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: sinan.lin at linux dot alibaba.com
Target Milestone: ---
gcc splits a movdi_32bit pattern into two insns after reload in rv32, which
brings constant propagation opportunities.
e.g.
```
long long int Data;
void init() {
Data = 0x0;
}
void init2() {
Data = 0xf00000000;
}
void init3() {
Data = 0xf0000000f;
}
```
asm output
```
init:
lui a5,%hi(Data)
li a3,0
li a4,0
sw a3,%lo(Data)(a5)
sw a4,%lo(Data+4)(a5)
ret
init2:
lui a5,%hi(Data)
li a2,0
li a3,15
sw a2,%lo(Data)(a5)
sw a3,%lo(Data+4)(a5)
ret
init3:
lui a5,%hi(Data)
li a2,15
li a3,15
sw a2,%lo(Data)(a5)
sw a3,%lo(Data+4)(a5)
ret
```
could be optimized into
```
init:
lui a5,%hi(Data)
sw zero,%lo(Data)(a5)
sw zero,%lo(Data+4)(a5)
ret
init2:
lui a5,%hi(Data)
li a2,15
sw zero,%lo(Data)(a5)
sw a2,%lo(Data+4)(a5)
ret
init3:
lui a5,%hi(Data)
li a2,15
sw a2,%lo(Data)(a5)
sw a2,%lo(Data+4)(a5)
ret
```
A similar case in AArch64
```
__int128 Data;
void init() {
Data = 0xfffff;
}
```
output
```
init:
adrp x0, .LANCHOR0
add x0, x0, :lo12:.LANCHOR0
mov x2, 1048575
mov x3, 0
stp x2, x3, [x0]
ret
```
could be optimized into
```
init:
adrp x0, .LANCHOR0
add x0, x0, :lo12:.LANCHOR0
mov x2, 1048575
stp x2, xzr, [x0]
ret
```
