This is related to PR51392.
Before this patch, the timeline view was rounding doubles to the first decimal,
using a logic similar to this:
```
double AverageTime = (double)Input / CumulativeExecutions;
double Result = floor((AverageTime * 10) + 0.5) / 10
```
Here, Input and CumulativeExecutions are both unsigned integers.
The last operation is what effectively performs the rounding of AverageTime.
PR51392 has been raised because - under specific -m32 configurations of GCC -
one of the timeline tests reports slighlty different values (due to a different
rounding choice).
This patch tries to minimise the propagation of floating-point error by
hoisting the multiply by 10, so that it is performed on the unsigned.
```
double AverageTime = (double)(Input * 10) / CumulativeExecutions;
floor(AverageTime + 0.5) / 10
```
So we are trading a floating point multiply for a integer multiply (which can be
expanded using a simple MUL or using an `ADD + LEA` sequence). This decrease in
floating point operations executed should also help with decreasing the error in
the computation..
Strictly speaking, that computation will always be potentially subject to error
(depending on what values are passed in input). However, this patch should
improve the situation and make bug like PR51392 less frequent.
(cherry picked from commit 45685a1fc4524579a25b03eb1a27e8fcb792afc7)
Applied clang-format to all files. Discarded BottleneckAnalysis.h
80-column width violation since it contains an example of report.
Caught some typos and minor style details.
Reviewed By: andreadb
Differential Revision: https://reviews.llvm.org/D105900
This patch addresses the last remaining problems reported in PR51008.
Previous fixes for PR51008 worked under the wrong assumption that code regions
are always named (except maybe for the default region, which was automatically
named "main").
In reality, it is quite common for users to declare multiple anonymous regions.
So we cannot really use the region name as the key string of a JSON object. In
practice, code region names are completely optional.
Using "main" for the default region was also problematic because there can be
another region with that same name.
This patch fixes these issues by introducing a json::array of regions. Each
region has a "Name" field, which would default to the empty string for anonymous
regions.
Added a few more tests to verify that the JSON file format is still valid, and
that multiple anonymous regions all appear in the final output.
This patch renames object "Resources" to "TargetInfo".
Moved the getJSONTargetInfo method from class InstructionView to the
PipelinePrinter.
Removed uses of std::stringstream.
Removed unused method View::printViewJSON().
Instead of printing each region individually when using JSON format,
this patch creates a JSON object which is updated with the values of
each region, printing them at the end. New test is added for JSON output
with multiple regions.
Bug: https://bugs.llvm.org/show_bug.cgi?id=51008
Reviewed By: andreadb
Differential Revision: https://reviews.llvm.org/D105618
This commit also makes some slight changes to the scheduling model for AMDGPU to set the RetireOOO flag for all scheduling classes.
This flag is only used by llvm-mca and allows instructions to retire out of order.
See the differential link below for a deeper explanation of everything.
Differential Revision: https://reviews.llvm.org/D104730
Based on the discussion in PR50922, minor changes have been done to properly
output a valid JSON. Removed "not implemented" keys.
Differential Revision: https://reviews.llvm.org/D105064
Change --max-timeline-cycles=0 to mean no limit on the number of cycles.
Use this in AMDGPU tests to show all instructions in the timeline view
instead of having it arbitrarily truncated.
Differential Revision: https://reviews.llvm.org/D104846
0 latency instructions now get processed and retired properly within the in-order pipeline. Had to fix a bug within TimelineView.cpp as well that would show up when a 0 latency instruction was the first instruction in the source.
Differential Revision: https://reviews.llvm.org/D104675
Put the dtor of mca::CustomBehaviour into the cpp file to avoid
undefined vtable when linking libLLVMMCACustomBehaviourAMDGPU as shared
library.
Differential Revision: https://reviews.llvm.org/D104401
The original change was pushed in main as commit f7a23ecece52.
It was then reverted by commit a04f01bab2 because it caused linker failures
on buildbots that don't build the AMDGPU target.
--
Some instructions are not defined well enough within the target’s scheduling
model for llvm-mca to be able to properly simulate its behaviour. The ideal
solution to this situation is to modify the scheduling model, but that’s not
always a viable strategy. Maybe other parts of the backend depend on that
instruction being modelled the way that it is. Or maybe the instruction is quite
complex and it’s difficult to fully capture its behaviour with tablegen. The
CustomBehaviour class (which I will refer to as CB frequently) is designed to
provide intuitive scaffolding for developers to implement the correct modelling
for these instructions.
More details are available in the original commit log message (f7a23ecece52).
Differential Revision: https://reviews.llvm.org/D104149
Some instructions are not defined well enough within the target’s scheduling
model for llvm-mca to be able to properly simulate its behaviour. The ideal
solution to this situation is to modify the scheduling model, but that’s not
always a viable strategy. Maybe other parts of the backend depend on that
instruction being modelled the way that it is. Or maybe the instruction is quite
complex and it’s difficult to fully capture its behaviour with tablegen. The
CustomBehaviour class (which I will refer to as CB frequently) is designed to
provide intuitive scaffolding for developers to implement the correct modelling
for these instructions.
Implementation details:
llvm-mca does its best to extract relevant register, resource, and memory
information from every MCInst when lowering them to an mca::Instruction. It then
uses this information to detect dependencies and simulate stalls within the
pipeline. For some instructions, the information that gets captured within the
mca::Instruction is not enough for mca to simulate them properly. In these
cases, there are two main possibilities:
1. The instruction has a dependency that isn’t detected by mca.
2. mca is incorrectly enforcing a dependency that shouldn’t exist.
For the rest of this discussion, I will be focusing on (1), but I have put some
thought into (2) and I may revisit it in the future.
So we have an instruction that has dependencies that aren’t picked up by mca.
The basic idea for both pipelines in mca is that when an instruction wants to be
dispatched, we first check for register hazards and then we check for resource
hazards. This is where CB is injected. If no register or resource hazards have
been detected, we make a call to CustomBehaviour::checkCustomHazard() to give
the target specific CB the chance to detect and enforce any custom dependencies.
The return value for checkCustomHazaard() is an unsigned int representing the
(minimum) number of cycles that the instruction needs to stall for. It’s fine to
underestimate this value because when StallCycles gets down to 0, we’ll end up
checking for all the hazards again before the instruction is actually
dispatched. However, it’s important not to overestimate the value and the more
accurate your estimate is, the more efficient mca’s execution can be.
In general, for checkCustomHazard() to be able to detect these custom
dependencies, it needs information about the current instruction and also all of
the instructions that are still executing within the pipeline. The mca pipeline
uses mca::Instruction rather than MCInst and the current information encoded
within each mca::Instruction isn’t sufficient for my use cases. I had to add a
few extra attributes to the mca::Instruction class and have them get set by the
MCInst during instruction building. For example, the current mca::Instruction
doesn’t know its opcode, and it also doesn’t know anything about its immediate
operands (both of which I had to add to the class).
With information about the current instruction, a list of all currently
executing instructions, and some target specific objects (MCSubtargetInfo and
MCInstrInfo which the base CB class has references to), developers should be
able to detect and enforce most custom dependencies within checkCustomHazard. If
you need more information than is present in the mca::Instruction, feel free to
add attributes to that class and have them set during the lowering sequence from
MCInst.
Fortunately, in the in-order pipeline, it’s very convenient for us to pass these
arguments to checkCustomHazard. The hazard checking is taken care of within
InOrderIssueStage::canExecute(). This function takes a const InstRef as a
parameter (representing the instruction that currently wants to be dispatched)
and the InOrderIssueStage class maintains a SmallVector<InstRef, 4> which holds
all of the currently executing instructions. For the out-of-order pipeline, it’s
a bit trickier to get the list of executing instructions and this is why I have
held off on implementing it myself. This is the main topic I will bring up when
I eventually make a post to discuss and ask for feedback.
CB is a base class where targets implement their own derived classes. If a
target specific CB does not exist (or we pass in the -disable-cb flag), the base
class is used. This base class trivially returns 0 from its checkCustomHazard()
implementation (meaning that the current instruction needs to stall for 0 cycles
aka no hazard is detected). For this reason, targets or users who choose not to
use CB shouldn’t see any negative impacts to accuracy or performance (in
comparison to pre-patch llvm-mca).
Differential Revision: https://reviews.llvm.org/D104149
This is based on the assumption that most simulated instructions don't define
more than one or two registers. This is true for example on x86, where
most instruction definitions don't declare more than one register write.
The default code region size has been increased from 8 to 16. This is based on
the assumption that, for small microbenchmarks, the typical code snippet size is
often less than 16 instructions.
mca::Instruction now uses bitfields to pack flags.
No functional change intended.
Moved the logic that checks for RAW hazards from the InOrderIssueStage to the
RegisterFile.
Changed how the InOrderIssueStage keeps track of backend stalls. Stall events
are now generated from method notifyStallEvent().
No functional change intended.
This makes it possible for targets to define their own MCObjectFileInfo.
This MCObjectFileInfo is then used to determine things like section alignment.
This is a follow up to D101462 and prepares for the RISCV backend defining the
text section alignment depending on the enabled extensions.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D101921
In order to create the code regions for llvm-mca to analyze, llvm-mca creates an
AsmCodeRegionGenerator and calls AsmCodeRegionGenerator::parseCodeRegions().
Within this function, both an MCAsmParser and MCTargetAsmParser are created so
that MCAsmParser::Run() can be used to create the code regions for us.
These parser classes were created for llvm-mc so they are designed to emit code
with an MCStreamer and MCTargetStreamer that are expected to be setup and passed
into the MCAsmParser constructor. Because llvm-mca doesn’t want to emit any
code, an MCStreamerWrapper class gets created instead and passed into the
MCAsmParser constructor. This wrapper inherits from MCStreamer and overrides
many of the emit methods to just do nothing. The exception is the
emitInstruction() method which calls Regions.addInstruction(Inst).
This works well and allows llvm-mca to utilize llvm-mc’s MCAsmParser to build
our code regions, however there are a few directives which rely on the
MCTargetStreamer. llvm-mc assumes that the MCStreamer that gets passed into the
MCAsmParser’s constructor has a valid pointer to an MCTargetStreamer. Because
llvm-mca doesn’t setup an MCTargetStreamer, when the parser encounters one of
those directives, a segfault will occur.
In x86, each one of these 7 directives will cause this segfault if they exist in
the input assembly to llvm-mca:
.cv_fpo_proc
.cv_fpo_setframe
.cv_fpo_pushreg
.cv_fpo_stackalloc
.cv_fpo_stackalign
.cv_fpo_endprologue
.cv_fpo_endproc
I haven’t looked at other targets, but I wouldn’t be surprised if some of the
other ones also have certain directives which could result in this same
segfault.
My proposed solution is to simply initialize an MCTargetStreamer after we
initialize the MCStreamerWrapper. The MCTargetStreamer requires an ostream
object, but we don’t actually want any of these directives to be emitted
anywhere, so I use an ostream created with the nulls() function. Since this
needs to happen after the MCStreamerWrapper has been initialized, it needs to
happen within the AsmCodeRegionGenerator::parseCodeRegions() function. The
MCTargetStreamer also needs an MCInstPrinter which is easiest to initialize
within the main() function of llvm-mca. So this MCInstPrinter gets constructed
within main() then passed into the parseCodeRegions() function as a parameter.
(If you feel like it would be appropriate and possible to create the
MCInstPrinter within the parseCodeRegions() function, then feel free to modify
my solution. That would stop us from having to pass it into the function and
would limit its scope / lifetime.)
My solution stops the segfault from happening and still passes all of the
current (expected) llvm-mca tests. I also added a new test for x86 that checks
for this segfault on an input that includes one of the .cv_fpo directives (this
test fails without my solution, but passes with it).
As far as I can tell, all of the functions that I modified are only called from
within llvm-mca so there shouldn’t be any worries about breaking other tools.
Differential Revision: https://reviews.llvm.org/D102709
This untangles the MCContext and the MCObjectFileInfo. There is a circular
dependency between MCContext and MCObjectFileInfo. Currently this dependency
also exists during construction: You can't contruct a MOFI without a MCContext
without constructing the MCContext with a dummy version of that MOFI first.
This removes this dependency during construction. In a perfect world,
MCObjectFileInfo wouldn't depend on MCContext at all, but only be stored in the
MCContext, like other MC information. This is future work.
This also shifts/adds more information to the MCContext making it more
available to the different targets. Namely:
- TargetTriple
- ObjectFileType
- SubtargetInfo
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D101462
lookupTarget() can update the passed triple argument. This happens
when no triple is given on the command line, and the architecture
argument does not match the architecture in the default triple.
For example, passing -march=aarch64 on the command line, and the
default triple being x86_64-windows-msvc, the triple is changed
to aarch64-windows-msvc.
However, this triple is not saved, and later in the code, the
triple is constructed again from the triple name, which is the
default triple at this point. Thus the default triple is passed
to constructor of MCSubtargetInfo instance.
The triple is only used determine the object file format, and by
chance, the AArch64 target also uses the COFF file format, and
all is fine. Obviously, the AArch64 target does not support all
available binary file formats, e.g. XCOFF and GOFF, and llvm-mca
crashes in this case.
The fix is to update the triple name with the changed triple
name for the target lookup. Then the default object file format
for the architecture is used, in the example ELF.
Reviewed By: andreadb, abhina.sreeskantharajan
Differential Revision: https://reviews.llvm.org/D100992
Problem:
On SystemZ we need to open text files in text mode. On Windows, files opened in text mode adds a CRLF '\r\n' which may not be desirable.
Solution:
This patch adds two new flags
- OF_CRLF which indicates that CRLF translation is used.
- OF_TextWithCRLF = OF_Text | OF_CRLF indicates that the file is text and uses CRLF translation.
Developers should now use either the OF_Text or OF_TextWithCRLF for text files and OF_None for binary files. If the developer doesn't want carriage returns on Windows, they should use OF_Text, if they do want carriage returns on Windows, they should use OF_TextWithCRLF.
So this is the behaviour per platform with my patch:
z/OS:
OF_None: open in binary mode
OF_Text : open in text mode
OF_TextWithCRLF: open in text mode
Windows:
OF_None: open file with no carriage return
OF_Text: open file with no carriage return
OF_TextWithCRLF: open file with carriage return
The Major change is in llvm/lib/Support/Windows/Path.inc to only set text mode if the OF_CRLF is set.
```
if (Flags & OF_CRLF)
CrtOpenFlags |= _O_TEXT;
```
These following files are the ones that still use OF_Text which I left unchanged. I modified all these except raw_ostream.cpp in recent patches so I know these were previously in Binary mode on Windows.
./llvm/lib/Support/raw_ostream.cpp
./llvm/lib/TableGen/Main.cpp
./llvm/tools/dsymutil/DwarfLinkerForBinary.cpp
./llvm/unittests/Support/Path.cpp
./clang/lib/StaticAnalyzer/Core/HTMLDiagnostics.cpp
./clang/lib/Frontend/CompilerInstance.cpp
./clang/lib/Driver/Driver.cpp
./clang/lib/Driver/ToolChains/Clang.cpp
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D99426
This is a follow-up for:
D98604 [MCA] Ensure that writes occur in-order
When instructions are aligned by the order of writes, they retire
in-order naturally. There is no need for an RCU, so it is disabled.
Differential Revision: https://reviews.llvm.org/D98628
This patch adds a pipeline to support in-order CPUs such as ARM
Cortex-A55.
In-order pipeline implements a simplified version of Dispatch,
Scheduler and Execute stages as a single stage. Entry and Retire
stages are common for both in-order and out-of-order pipelines.
Differential Revision: https://reviews.llvm.org/D94928
All these potential null pointer dereferences are reported by my static analyzer for null smart pointer dereferences, which has a different implementation from `alpha.cplusplus.SmartPtr`.
The checked pointers in this patch are initialized by Target::createXXX functions. When the creator function pointer is not correctly set, a null pointer will be returned, or the creator function may originally return a null pointer.
Some of them may not make sense as they may be checked before entering the function, but I fixed them all in this patch. I submit this fix because 1) similar checks are found in some other places in the LLVM codebase for the same return value of the function; and, 2) some of the pointers are dereferenced before they are checked, which may definitely trigger a null pointer dereference if the return value is nullptr.
Reviewed By: tejohnson, MaskRay, jpienaar
Differential Revision: https://reviews.llvm.org/D91410
No longer rely on an external tool to build the llvm component layout.
Instead, leverage the existing `add_llvm_componentlibrary` cmake function and
introduce `add_llvm_component_group` to accurately describe component behavior.
These function store extra properties in the created targets. These properties
are processed once all components are defined to resolve library dependencies
and produce the header expected by llvm-config.
Differential Revision: https://reviews.llvm.org/D90848
A SMLoc allows MCStreamer to report location-aware diagnostics, which
were previously done by adding SMLoc to various methods (e.g. emit*) in an ad-hoc way.
Since the file:line is most important, the column is less important and
the start token location suffices in many cases, this patch reverts
b7e7131af2dd7bdb03fa42a3bc1b4bc72ab95ce1
```
// old
symbol-binding-changed.s:6:8: error: local changed binding to STB_GLOBAL
.globl local
^
// new
symbol-binding-changed.s:6:1: error: local changed binding to STB_GLOBAL
.globl local
^
```
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D90511
including printing them.
Reviewers: andreadb, lebedev.ri
Differential Review: https://reviews.llvm.org/D86390
Introduces a new base class "InstructionView" that such views derive from.
Other views still use the "View" base class.
MCTargetOptionsCommandFlags.inc and CommandFlags.inc are headers which contain
cl::opt with static storage.
These headers are meant to be incuded by tools to make it easier to parametrize
codegen/mc.
However, these headers are also included in at least two libraries: lldCommon
and handle-llvm. As a result, when creating DYLIB, clang-cpp holds a reference
to the options, and lldCommon holds another reference. Linking the two in a
single executable, as zig does[0], results in a double registration.
This patch explores an other approach: the .inc files are moved to regular
files, and the registration happens on-demand through static declaration of
options in the constructor of a static object.
[0] https://bugzilla.redhat.com/show_bug.cgi?id=1756977#c5
Differential Revision: https://reviews.llvm.org/D75579
Lots of headers pass around MemoryBuffer objects, but very few open
them. Let those that do include FileSystem.h.
Saves ~250 includes of Chrono.h & FileSystem.h:
$ diff -u thedeps-before.txt thedeps-after.txt | grep '^[-+] ' | sort | uniq -c | sort -nr
254 - ../llvm/include/llvm/Support/FileSystem.h
253 - ../llvm/include/llvm/Support/Chrono.h
237 - ../llvm/include/llvm/Support/NativeFormatting.h
237 - ../llvm/include/llvm/Support/FormatProviders.h
192 - ../llvm/include/llvm/ADT/StringSwitch.h
190 - ../llvm/include/llvm/Support/FormatVariadicDetails.h
...
This requires duplicating the file_t typedef, which is unfortunate. I
sunk the choice of mapping mode down into the cpp file using variable
template specializations instead of class members in headers.
This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.
This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.
This doesn't actually modify StringRef yet, I'll do that in a follow-up.
It's been an empty target since r360498 and friends
(`git log --grep='Move InstPrinter files to MCTargetDesc.' llvm/lib/Target`),
but due to hwo the way these targets are structured it was silently
an empty target without anyone noticing.
No behavior change.
