https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106525
Bug ID: 106525
Summary: s390: Inefficient branchless conditionals for unsigned
long long
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: jens.seifert at de dot ibm.com
Target Milestone: ---
Created attachment 53409
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53409&action=edit
source code
1) -(a > b)
clgr %r2,%r3
lhi %r2,0
alcr %r2,%r2
sllg %r2,%r2,63
srag %r2,%r2,63
Last 2 could be merged to LCDFR. But optimal is:
slgrk %r2,%r3,%r2
slbgr %r2,%r2
lgfr %r2,%r2
Note: lgfr is not required => 2 instructions only.
2) -(a <= b)
slgr %r3,%r2
lhi %r2,0
alcr %r2,%r2
sllg %r2,%r2,63
srag %r2,%r2,63
Last 2 could be merged to LCDFR. But optimal is:
clgr %r2,%r3
slbgr %r2,%r2
lgfr %r2,%r2
Note: lgfr is not required => 2 instructions only.
3) unsigned 64-bit compare for qsort (a > b) - (a < b)
clgr %r2,%r3
lhi %r1,0
alcr %r1,%r1
clgr %r3,%r2
lhi %r2,0
alcr %r2,%r2
srk %r2,%r1,%r2
lgfr %r2,%r2
Optimal:
slgrk %r1,%r2,%r3
slgrk 0,%r3,%r2
slbgr %r2,%r3
slbgr %r1,%r2
lgfr %r2,%r1
Note: lgfr not required => 4 instructions only
