The current Intel Atom microarchitecture has a feature whereby
when a function returns early then it is slightly faster to execute
a sequence of NOP instructions to wait until the return address is ready,
as opposed to simply stalling on the ret instruction until
the return address is ready.
When compiling for X86 Atom only, this patch will run a pass,
called "X86PadShortFunction" which will add NOP instructions where less
than four cycles elapse between function entry and return.
It includes tests.
This patch has been updated to address Nadav's review comments
- Optimize only at >= O1 and don't do optimization if -Os is set
- Stores MachineBasicBlock* instead of BBNum
- Uses DenseMap instead of std::map
- Fixes placement of braces
Patch by Andy Zhang.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171879 91177308-0d34-0410-b5e6-96231b3b80d8
a TargetMachine to construct (and thus isn't always available), to an
analysis group that supports layered implementations much like
AliasAnalysis does. This is a pretty massive change, with a few parts
that I was unable to easily separate (sorry), so I'll walk through it.
The first step of this conversion was to make TargetTransformInfo an
analysis group, and to sink the nonce implementations in
ScalarTargetTransformInfo and VectorTargetTranformInfo into
a NoTargetTransformInfo pass. This allows other passes to add a hard
requirement on TTI, and assume they will always get at least on
implementation.
The TargetTransformInfo analysis group leverages the delegation chaining
trick that AliasAnalysis uses, where the base class for the analysis
group delegates to the previous analysis *pass*, allowing all but tho
NoFoo analysis passes to only implement the parts of the interfaces they
support. It also introduces a new trick where each pass in the group
retains a pointer to the top-most pass that has been initialized. This
allows passes to implement one API in terms of another API and benefit
when some other pass above them in the stack has more precise results
for the second API.
The second step of this conversion is to create a pass that implements
the TargetTransformInfo analysis using the target-independent
abstractions in the code generator. This replaces the
ScalarTargetTransformImpl and VectorTargetTransformImpl classes in
lib/Target with a single pass in lib/CodeGen called
BasicTargetTransformInfo. This class actually provides most of the TTI
functionality, basing it upon the TargetLowering abstraction and other
information in the target independent code generator.
The third step of the conversion adds support to all TargetMachines to
register custom analysis passes. This allows building those passes with
access to TargetLowering or other target-specific classes, and it also
allows each target to customize the set of analysis passes desired in
the pass manager. The baseline LLVMTargetMachine implements this
interface to add the BasicTTI pass to the pass manager, and all of the
tools that want to support target-aware TTI passes call this routine on
whatever target machine they end up with to add the appropriate passes.
The fourth step of the conversion created target-specific TTI analysis
passes for the X86 and ARM backends. These passes contain the custom
logic that was previously in their extensions of the
ScalarTargetTransformInfo and VectorTargetTransformInfo interfaces.
I separated them into their own file, as now all of the interface bits
are private and they just expose a function to create the pass itself.
Then I extended these target machines to set up a custom set of analysis
passes, first adding BasicTTI as a fallback, and then adding their
customized TTI implementations.
The fourth step required logic that was shared between the target
independent layer and the specific targets to move to a different
interface, as they no longer derive from each other. As a consequence,
a helper functions were added to TargetLowering representing the common
logic needed both in the target implementation and the codegen
implementation of the TTI pass. While technically this is the only
change that could have been committed separately, it would have been
a nightmare to extract.
The final step of the conversion was just to delete all the old
boilerplate. This got rid of the ScalarTargetTransformInfo and
VectorTargetTransformInfo classes, all of the support in all of the
targets for producing instances of them, and all of the support in the
tools for manually constructing a pass based around them.
Now that TTI is a relatively normal analysis group, two things become
straightforward. First, we can sink it into lib/Analysis which is a more
natural layer for it to live. Second, clients of this interface can
depend on it *always* being available which will simplify their code and
behavior. These (and other) simplifications will follow in subsequent
commits, this one is clearly big enough.
Finally, I'm very aware that much of the comments and documentation
needs to be updated. As soon as I had this working, and plausibly well
commented, I wanted to get it committed and in front of the build bots.
I'll be doing a few passes over documentation later if it sticks.
Commits to update DragonEgg and Clang will be made presently.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171681 91177308-0d34-0410-b5e6-96231b3b80d8
URL: http://llvm.org/viewvc/llvm-project?rev=171524&view=rev
Log:
The current Intel Atom microarchitecture has a feature whereby when a function
returns early then it is slightly faster to execute a sequence of NOP
instructions to wait until the return address is ready,
as opposed to simply stalling on the ret instruction
until the return address is ready.
When compiling for X86 Atom only, this patch will run a pass, called
"X86PadShortFunction" which will add NOP instructions where less than four
cycles elapse between function entry and return.
It includes tests.
Patch by Andy Zhang.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171603 91177308-0d34-0410-b5e6-96231b3b80d8
returns early then it is slightly faster to execute a sequence of NOP
instructions to wait until the return address is ready,
as opposed to simply stalling on the ret instruction
until the return address is ready.
When compiling for X86 Atom only, this patch will run a pass, called
"X86PadShortFunction" which will add NOP instructions where less than four
cycles elapse between function entry and return.
It includes tests.
Patch by Andy Zhang.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171524 91177308-0d34-0410-b5e6-96231b3b80d8
SSE transition penalty. The pass is enabled through the "x86-use-vzeroupper"
llc command line option. This is only the first step (very naive and
conservative one) to sketch out the idea, but proper DFA is coming next
to allow smarter decisions. Comments and ideas now and in further commits
will be very appreciated.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@138317 91177308-0d34-0410-b5e6-96231b3b80d8
specified in the same file that the library itself is created. This is
more idiomatic for CMake builds, and also allows us to correctly specify
dependencies that are missed due to bugs in the GenLibDeps perl script,
or change from compiler to compiler. On Linux, this returns CMake to
a place where it can relably rebuild several targets of LLVM.
I have tried not to change the dependencies from the ones in the current
auto-generated file. The only places I've really diverged are in places
where I was seeing link failures, and added a dependency. The goal of
this patch is not to start changing the dependencies, merely to move
them into the correct location, and an explicit form that we can control
and change when necessary.
This also removes a serialization point in the build because we don't
have to scan all the libraries before we begin building various tools.
We no longer have a step of the build that regenerates a file inside the
source tree. A few other associated cleanups fall out of this.
This isn't really finished yet though. After talking to dgregor he urged
switching to a single CMake macro to construct libraries with both
sources and dependencies in the arguments. Migrating from the two macros
to that style will be a follow-up patch.
Also, llvm-config is still generated with GenLibDeps.pl, which means it
still has slightly buggy dependencies. The internal CMake
'llvm-config-like' macro uses the correct explicitly specified
dependencies however. A future patch will switch llvm-config generation
(when using CMake) to be based on these deps as well.
This may well break Windows. I'm getting a machine set up now to dig
into any failures there. If anyone can chime in with problems they see
or ideas of how to solve them for Windows, much appreciated.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136433 91177308-0d34-0410-b5e6-96231b3b80d8
The first problem to fix is to stop creating synthetic *Table_gen
targets next to all of the LLVM libraries. These had no real effect as
CMake specifies that add_custom_command(OUTPUT ...) directives (what the
'tablegen(...)' stuff expands to) are implicitly added as dependencies
to all the rules in that CMakeLists.txt.
These synthetic rules started to cause problems as we started more and
more heavily using tablegen files from *subdirectories* of the one where
they were generated. Within those directories, the set of tablegen
outputs was still available and so these synthetic rules added them as
dependencies of those subdirectories. However, they were no longer
properly associated with the custom command to generate them. Most of
the time this "just worked" because something would get to the parent
directory first, and run tablegen there. Once run, the files existed and
the build proceeded happily. However, as more and more subdirectories
have started using this, the probability of this failing to happen has
increased. Recently with the MC refactorings, it became quite common for
me when touching a large enough number of targets.
To add insult to injury, several of the backends *tried* to fix this by
adding explicit dependencies back to the parent directory's tablegen
rules, but those dependencies didn't work as expected -- they weren't
forming a linear chain, they were adding another thread in the race.
This patch removes these synthetic rules completely, and adds a much
simpler function to declare explicitly that a collection of tablegen'ed
files are referenced by other libraries. From that, we can add explicit
dependencies from the smaller libraries (such as every architectures
Desc library) on this and correctly form a linear sequence. All of the
backends are updated to use it, sometimes replacing the existing attempt
at adding a dependency, sometimes adding a previously missing dependency
edge.
Please let me know if this causes any problems, but it fixes a rather
persistent and problematic source of build flakiness on our end.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136023 91177308-0d34-0410-b5e6-96231b3b80d8
backend. Moved some MCAsmInfo files down into the MCTargetDesc
sublibraries, removed some (i suspect long) dead files from other parts
of the CMake build, etc. Also copied the include directory hack from the
Makefile.
Finally, updated the lib deps. I spot checked this, and think its
correct, but review appreciated there.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135234 91177308-0d34-0410-b5e6-96231b3b80d8
target machine from those that are only needed by codegen. The goal is to
sink the essential target description into MC layer so we can start building
MC based tools without needing to link in the entire codegen.
First step is to refactor TargetRegisterInfo. This patch added a base class
MCRegisterInfo which TargetRegisterInfo is derived from. Changed TableGen to
separate register description from the rest of the stuff.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133782 91177308-0d34-0410-b5e6-96231b3b80d8
of testing for its presence at cmake time.
This way the build automatically regenerates the makefiles when a svn
update brings in a new sublibrary.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126068 91177308-0d34-0410-b5e6-96231b3b80d8
Next time the build is broken due to wrong library dependencies, just
try building again (if you are on some Unix and are building all LLVM
targets) or ask someone to commit the regenerated LLVMLibDeps.cmake.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110593 91177308-0d34-0410-b5e6-96231b3b80d8
pass that inserted it.
It is no longer necessary to limit the live ranges of FP registers to a single
basic block.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108536 91177308-0d34-0410-b5e6-96231b3b80d8
bit (we're not trying to build a shared library yet) and generating
the X86GenEDInfo.inc and ARMGenEDInfo.inc files as necessary.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101188 91177308-0d34-0410-b5e6-96231b3b80d8
On Nehalem and newer CPUs there is a 2 cycle latency penalty on using a register
in a different domain than where it was defined. Some instructions have
equvivalents for different domains, like por/orps/orpd.
The SSEDomainFix pass tries to minimize the number of domain crossings by
changing between equvivalent opcodes where possible.
This is a work in progress, in particular the pass doesn't do anything yet. SSE
instructions are tagged with their execution domain in TableGen using the last
two bits of TSFlags. Note that not all instructions are tagged correctly. Life
just isn't that simple.
The SSE execution domain issue is very similar to the ARM NEON/VFP pipeline
issue handled by NEONMoveFixPass. This pass may become target independent to
handle both.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99524 91177308-0d34-0410-b5e6-96231b3b80d8
This is work in progress. So far, SSE execution domain tables are added to
X86InstrInfo, and a skeleton pass is enabled with -sse-domain-fix.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99345 91177308-0d34-0410-b5e6-96231b3b80d8
- Although it would be nice to allow this decoupling, the assembler needs to be able to reason about MCSymbolRefExprs in too many places to make this viable. We can use a target specific encoding of the variant if this becomes an issue.
- This patch also extends llvm-mc to support parsing of the modifiers, as opposed to lumping them in with the symbol.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@98592 91177308-0d34-0410-b5e6-96231b3b80d8
incarnations), integrated into the MC framework.
The disassembler is table-driven, using a custom TableGen backend to
generate hierarchical tables optimized for fast decode. The disassembler
consumes MemoryObjects and produces arrays of MCInsts, adhering to the
abstract base class MCDisassembler (llvm/MC/MCDisassembler.h).
The disassembler is documented in detail in
- lib/Target/X86/Disassembler/X86Disassembler.cpp (disassembler runtime)
- utils/TableGen/DisassemblerEmitter.cpp (table emitter)
You can test the disassembler by running llvm-mc -disassemble for i386
or x86_64 targets. Please let me know if you encounter any problems
with it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91749 91177308-0d34-0410-b5e6-96231b3b80d8
