https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97464
Bug ID: 97464
Summary: Missed redundant store optimization opportunity
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: pdimov at gmail dot com
Target Milestone: ---
The code
void f( int& x, float& y )
{
++x;
y = 1;
--x;
}
compiles to
f(int&, float&):
mov eax, DWORD PTR [rdi]
mov DWORD PTR [rsi], 0x3f800000
mov DWORD PTR [rdi], eax
ret
(https://godbolt.org/z/so4h3v)
but the load from, and the store to, [rdi] are redundant. It's obvious that
TBAA is active, but it for some reason doesn't go far enough.
This is a simplified example from "realer" code where x is a reference count
whose unnecessary manipulations could have been optimized out entirely.
