unsigned long le1_bit(unsigned long x) {
return x == 0 || (x & (x - 1)) == 0;
}
yields with 4.0.0 20050201:
le1_bit: clr v0
lda t0,-1(a0)
beq a0,L1
and a0,t0,t0
bne t0,L2
L1: lda v0,1
L2: ret
that is, two unnecessary jumps as compared to the completely straight-forward
translation:
le1_bit: cmpeq a0,0,t0
lda t1,-1(a0)
and a0,t1,t1
cmpeq t1,0,t1
or t0,t1,v0
ret
--
Summary: Unnecessary jumps for comparisons
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P2
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: falk at debian dot org
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: alphaev68-unknown-linux-gnu
GCC host triplet: alphaev68-unknown-linux-gnu
GCC target triplet: alphaev68-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19778
