https://bugs.llvm.org/show_bug.cgi?id=49924
Bug ID: 49924
Summary: Missed load elimination
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
struct A
{
int x;
} *A_ptr;
struct B
{
struct A a;
int y;
} *B_ptr;
int
test ()
{
struct A ap = { 0 };
B_ptr->y = 123;
*A_ptr = ap;
return B_ptr->y;
}
ICC/GCC:
test():
mov rax, QWORD PTR B_ptr[rip] #15.3
mov rdx, QWORD PTR A_ptr[rip] #16.4
mov DWORD PTR [4+rax], 123 #15.3
mov eax, 123 #17.10
mov DWORD PTR [rdx], 0 #16.4
ret #17.10
A_ptr:
B_ptr:
LLVM trunk:
test(): # @test()
mov rax, qword ptr [rip + B_ptr]
mov dword ptr [rax + 4], 123
mov rax, qword ptr [rip + A_ptr]
mov dword ptr [rax], 0
mov rax, qword ptr [rip + B_ptr]
mov eax, dword ptr [rax + 4]
ret
A_ptr:
.quad 0
B_ptr:
.quad 0
https://godbolt.org/z/Pxx66j44r
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