https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100046
Bug ID: 100046
Summary: compare with itself
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: luc.vanoostenryck at gmail dot com
Target Milestone: ---
Created attachment 50569
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50569&action=edit
compare with itself
The attached file reproduced here:
int b3_06(int x, int y, int z) {
int a = (x | z) ^ (y | z);
int b = (x ^ y) & ~z;
return a == b;
}
The generated assembly for for arm64 is:
b3_06:
eor w3, w1, w0
bic w3, w3, w2
cmp w3, w3
cset w0, eq
ret
So, GCC is able to see that both expressions are equivalent. Nice.
But then there is this compare with itself :(
The problem seems to exist forever on all targets (see
https://gcc.godbolt.org/z/qrYWsznof ).
