Summary:
Targets often have instructions that can sign-extend certain cases faster
than the equivalent shift-left/arithmetic-shift-right. Such cases can be
identified by matching a shift-left/shift-right pair but there are some
issues with this in the context of combines. For example, suppose you can
sign-extend 8-bit up to 32-bit with a target extend instruction.
%1:_(s32) = G_SHL %0:_(s32), i32 24 # (I've inlined the G_CONSTANT for brevity)
%2:_(s32) = G_ASHR %1:_(s32), i32 24
%3:_(s32) = G_ASHR %2:_(s32), i32 1
would reasonably combine to:
%1:_(s32) = G_SHL %0:_(s32), i32 24
%2:_(s32) = G_ASHR %1:_(s32), i32 25
which no longer matches the special case. If your shifts and extend are
equal cost, this would break even as a pair of shifts but if your shift is
more expensive than the extend then it's cheaper as:
%2:_(s32) = G_SEXT_INREG %0:_(s32), i32 8
%3:_(s32) = G_ASHR %2:_(s32), i32 1
It's possible to match the shift-pair in ISel and emit an extend and ashr.
However, this is far from the only way to break this shift pair and make
it hard to match the extends. Another example is that with the right
known-zeros, this:
%1:_(s32) = G_SHL %0:_(s32), i32 24
%2:_(s32) = G_ASHR %1:_(s32), i32 24
%3:_(s32) = G_MUL %2:_(s32), i32 2
can become:
%1:_(s32) = G_SHL %0:_(s32), i32 24
%2:_(s32) = G_ASHR %1:_(s32), i32 23
All upstream targets have been configured to lower it to the current
G_SHL,G_ASHR pair but will likely want to make it legal in some cases to
handle their faster cases.
To follow-up: Provide a way to legalize based on the constant. At the
moment, I'm thinking that the best way to achieve this is to provide the
MI in LegalityQuery but that opens the door to breaking core principles
of the legalizer (legality is not context sensitive). That said, it's
worth noting that looking at other instructions and acting on that
information doesn't violate this principle in itself. It's only a
violation if, at the end of legalization, a pass that checks legality
without being able to see the context would say an instruction might not be
legal. That's a fairly subtle distinction so to give a concrete example,
saying %2 in:
%1 = G_CONSTANT 16
%2 = G_SEXT_INREG %0, %1
is legal is in violation of that principle if the legality of %2 depends
on %1 being constant and/or being 16. However, legalizing to either:
%2 = G_SEXT_INREG %0, 16
or:
%1 = G_CONSTANT 16
%2:_(s32) = G_SHL %0, %1
%3:_(s32) = G_ASHR %2, %1
depending on whether %1 is constant and 16 does not violate that principle
since both outputs are genuinely legal.
Reviewers: bogner, aditya_nandakumar, volkan, aemerson, paquette, arsenm
Subscribers: sdardis, jvesely, wdng, nhaehnle, rovka, kristof.beyls, javed.absar, hiraditya, jrtc27, atanasyan, Petar.Avramovic, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D61289
llvm-svn: 368487
https://reviews.llvm.org/D65698
This adds a KnownBits analysis pass for GISel. This was done as a
pass (compared to static functions) so that we can add other features
such as caching queries(within a pass and across passes) in the future.
This patch only adds the basic pass boiler plate, and implements a lazy
non caching knownbits implementation (ported from SelectionDAG). I've
also hooked up the AArch64PreLegalizerCombiner pass to use this - there
should be no compile time regression as the analysis is lazy.
llvm-svn: 368065
Extract the sources to the GCD of the original size and target size,
padding with implicit_def as necessary.
Also fix the case where the requested source type is wider than the
original result type. This was ignoring the type, and just using the
destination. Do the operation in the requested type and truncate back.
llvm-svn: 366367
Use an anyext to the requested type for the leftover operand to
produce a slightly wider type, and then truncate the final merge.
I have another implementation almost ready which handles arbitrary
widens, but I think it produces worse code in this example (which I
think is 90% due to not folding redundant copies or folding out
implicit_def users), so I wanted to add this as a baseline first.
llvm-svn: 366366
Avoids using a plain unsigned for registers throughoug codegen.
Doesn't attempt to change every register use, just something a little
more than the set needed to build after changing the return type of
MachineOperand::getReg().
llvm-svn: 364191
This was ignoring the flag on fneg, and using the source instruction's
flags. Also fixes tests missing from r358702.
Note the expansion itself isn't correct without nnan, but that should
be fixed separately.
llvm-svn: 363637
Because CodeGen can't depend on GlobalISel, we need a way to encapsulate the CSE
configs that can be passed between TargetPassConfig and the targets' custom
pass configs. This CSEConfigBase allows targets to create custom CSE configs
which is then used by the GISel passes for the CSEMIRBuilder.
This support will be used in a follow up commit to allow constant-only CSE for
-O0 compiles in D60580.
llvm-svn: 358368
This fixes two problems with CSE done in buildConstant. First, this
would hit an assert when used with a vector result type. Solve this by
allowing CSE on the vector elements, but not on the result vector for
now.
Second, this was also performing the CSE based on the input
ConstantInt pointer. The underlying buildConstant could potentially
convert the constant depending on the result type, giving in a
different ConstantInt*. Stop allowing the APInt and ConstantInt forms
from automatically casting to the result type to avoid any similar
problems in the future.
llvm-svn: 353077
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
https://reviews.llvm.org/D52803
This patch adds support to continuously CSE instructions during
each of the GISel passes. It consists of a GISelCSEInfo analysis pass
that can be used by the CSEMIRBuilder.
llvm-svn: 351283
Summary:
This allows us to register it with the MachineFunction delegate and be
notified automatically about erasure and creation of instructions. However,
we still need explicit notification for modifications such as those caused
by setReg() or replaceRegWith().
There is a catch with this though. The notification for creation is
delivered before any operands can be added. While appropriate for
scheduling combiner work. This is unfortunate for debug output since an
opcode by itself doesn't provide sufficient information on what happened.
As a result, the work list remembers the instructions (when debug output is
requested) and emits a more complete dump later.
Another nit is that the MachineFunction::Delegate provides const pointers
which is inconvenient since we want to use it to schedule future
modification. To resolve this GISelWorkList now has an optional pointer to
the MachineFunction which describes the scope of the work it is permitted
to schedule. If a given MachineInstr* is in this function then it is
permitted to schedule work to be performed on the MachineInstr's. An
alternative to this would be to remove the const from the
MachineFunction::Delegate interface, however delegates are not permitted
to modify the MachineInstr's they receive.
In addition to this, the observer has three interface changes.
* erasedInstr() is now erasingInstr() to indicate it is about to be erased
but still exists at the moment.
* changingInstr() and changedInstr() have been added to report changes
before and after they are made. This allows us to trace the changes
in the debug output.
* As a convenience changingAllUsesOfReg() and
finishedChangingAllUsesOfReg() will report changingInstr() and
changedInstr() for each use of a given register. This is primarily useful
for changes caused by MachineRegisterInfo::replaceRegWith()
With this in place, both combine rules have been updated to report their
changes to the observer.
Finally, make some cosmetic changes to the debug output and make Combiner
and CombinerHelp
Reviewers: aditya_nandakumar, bogner, volkan, rtereshin, javed.absar
Reviewed By: aditya_nandakumar
Subscribers: mgorny, rovka, kristof.beyls, llvm-commits
Differential Revision: https://reviews.llvm.org/D52947
llvm-svn: 349167
Summary:
In addition to knowing that an instruction is changed. It's also useful to
know when it's about to change. For example, it might print the instruction so
you can track the changes in a debug log, it might remove it from some queue
while it's being worked on, or it might want to change several instructions as
a single transaction and act on all the changes at once.
Added changingInstr() to all existing uses of changedInstr()
Reviewers: aditya_nandakumar
Reviewed By: aditya_nandakumar
Subscribers: rovka, kristof.beyls, llvm-commits
Differential Revision: https://reviews.llvm.org/D55623
llvm-svn: 348992
Summary:
There's little of interest that can be done to an already-erased instruction.
You can't inspect it, write it to a debug log, etc. It ought to be notification
that we're about to erase it. Rename the function to clarify the timing of the
event and reflect current usage.
Also fixed one case where we were trying to print an erased instruction.
Reviewers: aditya_nandakumar
Reviewed By: aditya_nandakumar
Subscribers: rovka, kristof.beyls, llvm-commits
Differential Revision: https://reviews.llvm.org/D55611
llvm-svn: 348976
https://reviews.llvm.org/D55294
Previously MachineIRBuilder::buildInstr used to accept variadic
arguments for sources (which were either unsigned or
MachineInstrBuilder). While this worked well in common cases, it doesn't
allow us to build instructions that have multiple destinations.
Additionally passing in other optional parameters in the end (such as
flags) is not possible trivially. Also a trivial call such as
B.buildInstr(Opc, Reg1, Reg2, Reg3)
can be interpreted differently based on the opcode (2defs + 1 src for
unmerge vs 1 def + 2srcs).
This patch refactors the buildInstr to
buildInstr(Opc, ArrayRef<DstOps>, ArrayRef<SrcOps>)
where DstOps and SrcOps are typed unions that know how to add itself to
MachineInstrBuilder.
After this patch, most invocations would look like
B.buildInstr(Opc, {s32, DstReg}, {SrcRegs..., SrcMIBs..});
Now all the other calls (such as buildAdd, buildSub etc) forward to
buildInstr. It also makes it possible to build instructions with
multiple defs.
Additionally in a subsequent patch, we should make it possible to add
flags directly while building instructions.
Additionally, the main buildInstr method is now virtual and other
builders now only have to override buildInstr (for say constant
folding/cseing) is straightforward.
Also attached here (https://reviews.llvm.org/F7675680) is a clang-tidy
patch that should upgrade the API calls if necessary.
llvm-svn: 348815
https://reviews.llvm.org/D54980
This provides a standard API across GISel passes to observe and notify
passes about changes (insertions/deletions/mutations) to MachineInstrs.
This patch also removes the recordInsertion method in MachineIRBuilder
and instead provides method to setObserver.
Reviewed by: vkeles.
llvm-svn: 348406
We can now select CLZ via the TableGen'erated code, so support G_CTLZ
and G_CTLZ_ZERO_UNDEF throughout the pipeline for types <= s32.
Legalizer:
If the CLZ instruction is available, use it for both G_CTLZ and
G_CTLZ_ZERO_UNDEF. Otherwise, use a libcall for G_CTLZ_ZERO_UNDEF and
lower G_CTLZ in terms of it.
In order to achieve this we need to add support to the LegalizerHelper
for the legalization of G_CTLZ_ZERO_UNDEF for s32 as a libcall (__clzsi2).
We also need to allow lowering of G_CTLZ in terms of G_CTLZ_ZERO_UNDEF
if that is supported as a libcall, as opposed to just if it is Legal or
Custom. Due to a minor refactoring of the helper function in charge of
this, we will also allow the same behaviour for G_CTTZ and G_CTPOP.
This is not going to be a problem in practice since we don't yet have
support for treating G_CTTZ and G_CTPOP as libcalls (not even in
DAGISel).
Reg bank select:
Map G_CTLZ to GPR. G_CTLZ_ZERO_UNDEF should not make it to this point.
Instruction select:
Nothing to do.
llvm-svn: 347545
MachineModuleInfo can only be used in code using lib/CodeGen, hence we
can keep a more specific reference to LLVMTargetMachine rather than just
TargetMachine around.
llvm-svn: 346182
This reverts commit d1341152d91398e9a882ba2ee924147ea2f9b589.
This patch originally made use of Nested MachineIRBuilder buildInstr
calls, and since order of argument processing is not well defined, the
instructions were built slightly in a different order (still correct).
I've removed the nested buildInstr calls to have a defined order now.
Patch was tested by Mikael.
llvm-svn: 340309
Daniel Sanders