https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124009
Bug ID: 124009
Summary: Improve select between -1,1
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: law at gcc dot gnu.org
Target Milestone: ---
int foo(int x, int y) { return (y < x) ? 1 : -1; }
WHen compiled on riscv64 with -O2 -march=rv64gcbv_zicond we get something like
this:
slt a1,a1,a0 # 27 [c=4 l=4] slt_didi3
li a5,2 # 28 [c=4 l=4] *movdi_64bit/1
czero.eqz a0,a5,a1 # 29 [c=4 l=4] *czero.eqz.didi
addi a0,a0,-1 # 17 [c=4 l=4] *adddi3/1
But it seems like slt to generate 0/1, then shifting that left resulting in
0/2, then subtracting 1 to get -1,1 would be a better sequence. Obviously
there are generalizations that could be done here as well.
