https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94026
Bug ID: 94026
Summary: combine missed opportunity to simplify comparisons
with zero
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: felix.yang at huawei dot com
Target Milestone: ---
Created attachment 47966
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47966&action=edit
proposed patch to fix this issue
Simple test case:
int
foo (int c, int d)
{
int a = (c >> d) & 7;
if (a >= 2) {
return 1;
}
return 0;
}
Compile option: gcc -S -O2 test.c
On aarch64, GCC trunk emits 4 instrunctions:
asr w0, w0, 8
tst w0, 6
cset w0, ne
ret
which can be further simplified into:
tst x0, 1536
cset w0, ne
ret
We see the same issue on other targets such as i386 and x86-64.
Attached please find proposed patch for this issue.
