https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95704
--- Comment #3 from Jens Seifert <jens.seifert at de dot ibm.com> ---
GCC 8.3 generates:
_Z3shloy:
.LFB0:
.cfi_startproc
addi 9,5,-64
cmpwi 7,9,0
blt 7,.L2
sld 4,3,9
li 3,0
blr
.p2align 4,,15
.L2:
srdi 9,3,1
subfic 10,5,63
sld 4,4,5
srd 9,9,10
sld 3,3,5
or 4,9,4
blr
.long 0
.byte 0,9,0,0,0,0,0,0
.cfi_endproc
8 instructions if taking L2. The branch free code I propsed:
_Z15shl_branch_lessoy:
.LFB1:
.cfi_startproc
rldicl 5,5,0,32
subfic 9,5,64
addi 10,5,-64
sld 10,3,10
srd 9,3,9
sld 4,4,5
or 9,9,10
or 4,9,4
sld 3,3,5
blr
8 instructions no branch. Almost everything can be executed in parallel.
rldicl 5,5,0,32 gets added by gcc, which is not necessary.
