Intel Itanium 9150M, Manual

Page: 29 / 420

3:20 Volume 3: Instruction Reference
br
br — Branch
Format: (
qp
) br.
btype
.
bwh
.
ph
.
dh target
25
ip_relative_form B1
(
qp
) br.
btype
.
bwh
.
ph
.
dh b
1
=
target
25
call_form, ip_relative_form B3
br.
btype
.
bwh
.
ph
.
dh target
25
counted_form, ip_relative_form B2
br.
ph
.
dh target
25
pseudo-op
(
qp
) br.
btype
.
bwh
.
ph
.
dh b
2
indirect_form B4
(
qp
) br.
btype
.
bwh
.
ph
.
dh b
1
=
b
2
call_form, indirect_form B5
br.
ph
.
dh b
2
pseudo-op
Description:
A branch condition is evaluated, and either a branch is taken, or execution continues
with the next sequential instruction. The execution of a branch logically follows the
execution of all previous non-branch instructions in the same instruction group. On a
taken branch, execution begins at slot 0.
Branches can be either IP-relative, or indirect. For IP-relative branches, the
target
25
operand, in assembly, specifies a label to branch to. This is encoded in the branch
instruction as a signed immediate displacement (
imm
21
) between the target bundle and
the bundle containing this instruction (
imm
21
=
target
25
- IP >> 4). For indirect branches,
the target address is taken from BR
b
2
.
There are two pseudo-ops for unconditional branches. These are encoded like a
conditional branch (
btype
= cond), with the
qp
field specifying PR 0, and with the
bwh
hint of sptk.
The branch type determines how the branch condition is calculated and whether the
branch has other effects (such as writing a link register). For the basic branch types,
Table 2-6. Branch Types
btype Function Branch Condition Target Address
cond or none Conditional branch Qualifying predicate IP-rel or Indirect
call Conditional procedure call Qualifying predicate IP-rel or Indirect
ret Conditional procedure return Qualifying predicate Indirect
ia Invoke IA-32 instruction set Unconditional Indirect
cloop Counted loop branch Loop count IP-rel
ctop, cexit Mod-scheduled counted loop Loop count and epilog
count IP-rel
wtop, wexit Mod-scheduled while loop Qualifying predicate and
epilog count IP-rel