Major refactoring of the branch predictor unit.
- Clearer control flow of the main branch predictor
- Remove `uncondBranch` and `btbUpdate` functions in favour of a
common `historyUpdate` function. There is now only one lookup
function for conditional branches and the new `historyUpdate` for
speculative history update.
- Added a new *target provider* class.
- More expressive statistics depending on the different branch types.
- Cleanup the branch history management
Change-Id: I21fa555b5663e4abad7c836fc1d41a9c8b205263
Signed-off-by: David Schall <david.schall@ed.ac.uk>
The return address stack (RAS) is restructured to be a separate SimObject.
This enables disabling the RAS and better separation of the functionality.
Furthermore, easier statistics and debugging.
Change-Id: I8aacf7d4c8e308165d0e7e15bc5a5d0df77f8192
Signed-off-by: David Schall <david.schall@ed.ac.uk>
Simplify indirect predictor interface. Several of the existing
functions where merged together into four clear once. Those
four are similar to the main direction predictor interface.
'lookup', 'update', 'squash' and 'commit'. This makes the
interface much more clear, allows better functionality isolation
and makes it simpler to develop new predictor models.
A new parameter is added to allow additional buffer space for
speculative path history.
Change-Id: I6d6b43965b2986ef959953a64c428e50bc68d38e
Signed-off-by: David Schall <david.schall@ed.ac.uk>
- A new abstract BTB class is created to enable different BTB
implementations. The new BTB class gets its own parameter
and stats.
- An enum is added to differentiate branch instruction types.
This enum is used to enhance statistics and BPU management.
- The existing BTB is moved into `simple_btb` as default.
- An additional function is added to store the static instruction in
the BTB. This function is used for the decoupled front-end.
- Update configs to match new BTB parameters.
Change-Id: I99b29a19a1b57e59ea2b188ed7d62a8b79426529
Signed-off-by: David Schall <david.schall@ed.ac.uk>
The DEBUG macro is not part of any compiler standards (differently from
NDEBUG, which elides assertions).
It is only meant to differentiate gem5.debug from .fast and .opt builds.
gem5 developers have used it to insert helper code that is supposed to
aid the debugging process in case anything goes wrong.
This generic name is likely to clash with other libraries linked with
gem5. This is the case of DRAMSim as an example.
Rather than using undef tricks, we just inject a GEM5_DEBUG macro
for gem5.debug builds.
Change-Id: Ie913ca30da615bd0075277a260bbdbc397b7ec87
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/69079
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
This makes what are configuration and what are internal SCons variables
explicit and separate, and makes it unnecessary to call out what
variables to export to C++.
These variables will also be plumbed into and out of kconfiglib in later
changes.
Change-Id: Iaf5e098d7404af06285c421dbdf8ef4171b3f001
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/56892
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
The default value of IPredEntry::tag is 0, and if we just blindly
compare the tag we're looking for against this value, we might run into
cases where we match against an uninitialized IPredEntry. In that case,
IPredEntry::target has not been initialized, and if we try to use it in
lookup(...) we'll dereference nullptr and segfault.
To avoid that, we can just add one additional check that makes sure that
not only does the tag of the IPredEntry match, but also that the value
of target is not null, and so the IPredEntry *actually* has tag 0 and
isn't just uninitialized.
Change-Id: I892d0df7c00a0a4cd3ca215fe3a7586ddbca9395
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/53403
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Apply the gem5 namespace to the codebase.
Some anonymous namespaces could theoretically be removed,
but since this change's main goal was to keep conflicts
at a minimum, it was decided not to modify much the
general shape of the files.
A few missing comments of the form "// namespace X" that
occurred before the newly added "} // namespace gem5"
have been added for consistency.
std out should not be included in the gem5 namespace, so
they weren't.
ProtoMessage has not been included in the gem5 namespace,
since I'm not familiar with how proto works.
Regarding the SystemC files, although they belong to gem5,
they actually perform integration between gem5 and SystemC;
therefore, it deserved its own separate namespace.
Files that are automatically generated have been included
in the gem5 namespace.
The .isa files currently are limited to a single namespace.
This limitation should be later removed to make it easier
to accomodate a better API.
Regarding the files in util, gem5:: was prepended where
suitable. Notice that this patch was tested as much as
possible given that most of these were already not
previously compiling.
Change-Id: Ia53d404ec79c46edaa98f654e23bc3b0e179fe2d
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/46323
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>
As part of recent decisions regarding namespace
naming conventions, all namespaces will be changed
to snake case.
::Stats became ::statistics.
"statistics" was chosen over "stats" to avoid generating
conflicts with the already existing variables (there are
way too many "stats" in the codebase), which would make
this patch even more disturbing for the users.
Change-Id: If877b12d7dac356f86e3b3d941bf7558a4fd8719
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45421
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
As part of recent decisions regarding namespace
naming conventions, all namespaces will be changed
to snake case.
::ProbePoints became ::probing.
"probing" was chosen over "probe_points" because the
namespace contains more than solely probe points; it
contains all classes related to the act of probing.
Change-Id: I44567974a521707593739a2bd5933391803e5b51
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45412
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
The only thing brought in by arch/types.hh is TheISA::PCState. Instead
of having the other types around where they could be used accidentally,
and to make it more obvious what's being exported, this change splits
PCState out into a new switching header called arch/pcstate.hh. The
original arch/types.hh is no longer a switching header, and includes
pcstate.hh.
Change-Id: I8dfd298349e4565f316f7b9a028703289ada6010
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40177
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
The nullStaticInstPtr was low overhead, but the nopStaticInstPtr needed
an actual StaticInst implementation it could point to, and that brought
with it some (minor) additional dependencies. Specifically, the
implementation of advancePC needs the definition of TheISA::PCState,
while all other signatures/impementations in StaticInst are already
passing around that type by reference or could be made to, reducing
dependencies further.
Change-Id: I9ac6a6e5a3106858ea1fc727648f61dc39738a59
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42968
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
These were not caught by the previous patches because
the grep used ignored:
- anonymous structures
(e.g., "struct {")
- opening braces without leading spaces
(e.g., "struct Name{"),
- weird chars in auto-generation files
(e.g., "struct $name {").
- extra characters after the opening brace.
(e.g., "struct Name { // Comment")
- typedefs (note that this is not caught by the verifier)
(e.g., "typedef struct Name {")
Most of this has been fixed be grepping structures
with the following regex:
grep -nrE --exclude-dir=systemc \
"^ *(typedef)* *(struct|class|enum|union) [^{]*{$" src/
The following makes sure that "struct{" is captured:
grep -nrE --exclude-dir=systemc \
"^ *(struct|class|enum|union){" src/
To find cases that contain a comment after the
opening brace:
grep -nrE --exclude-dir=systemc \
"^ *(struct|class|enum|union)[^{]*{\s*//" src/
Change-Id: I9f822bed628d13b1a09ccd6059373aff63a8d7bd
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/43505
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
In most ISAs except MIPS and Power, this was implemented as
inst->advancePC(). It works just fine to call this function all the
time, but the idea had originally been that for ISAs which could simply
advance the PC using the PC itself, they could save the virtual function
call. Since the only ISAs which could skip the call were MIPS and Power,
and neither is at the point where that level of performance tuning
matters, this function can be collapsed with little downside.
If this turns out to be a performance bottleneck in the future, the way
the PC is managed could be revisited to see if we can factor out this
trip to the instruction object in the first place.
Change-Id: I533d1ad316e5c936466c529b7f1238a9ab87bd1c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39335
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Alex Dutu <alexandru.dutu@amd.com>
The systemc dir was not included in this fix.
First it was identified that there were only occurrences
at 0, 1, 2 and 3 levels of indentation (and a single
occurrence of 2 and 3 spaces), using:
grep -nrE --exclude-dir=systemc \
"^ *struct [A-Za-z].* {$" src/
Then the following commands were run to replace:
<indent level>struct X ... {
by:
<indent level>struct X ...
<indent level>{
Level 0:
grep -nrl --exclude-dir=systemc
"^struct [A-Za-z].* {$" src/ | \
xargs sed -Ei \
's/^struct ([A-Za-z].*) \{$/struct \1\n\{/g'
Level 1:
grep -nrl --exclude-dir=systemc \
"^ struct [A-Za-z].* {$" src/ | \
xargs sed -Ei \
's/^ struct ([A-Za-z].*) \{$/ struct \1\n \{/g'
and so on.
Change-Id: I362ef58c86912dabdd272c7debb8d25d587cd455
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39017
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
The systemc dir was not included in this fix.
First it was identified that there were only occurrences
at 0, 1, and 2 levels of indentation, using:
grep -nrE --exclude-dir=systemc \
"^ *class [A-Za-z].* {$" src/
Then the following commands were run to replace:
<indent level>class X ... {
by:
<indent level>class X ...
<indent level>{
Level 0:
grep -nrl --exclude-dir=systemc
"^class [A-Za-z].* {$" src/ | \
xargs sed -Ei \
's/^class ([A-Za-z].*) \{$/class \1\n\{/g'
Level 1:
grep -nrl --exclude-dir=systemc \
"^ class [A-Za-z].* {$" src/ | \
xargs sed -Ei \
's/^ class ([A-Za-z].*) \{$/ class \1\n \{/g'
and so on.
Change-Id: I17615ce16a333d69867b27c7bae0f4fdafd8b2eb
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39015
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
This was an inline function defined for each ISA, but really it makes
more sense for it to be defined by the instruction classes. The actual
return address for any given instruction can best be calculated when you
know what that instruction actually does, and also the instructions will
know about ISA level PC management.
Change-Id: I2c5203aefa90f2f26ecd94e82b925c6b552e33d3
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39324
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
