This gets rid of some of the gory splitting details in RAGreedy and
makes them available to future SplitKit clients.
Slightly generalize the functionality to support multi-way splitting.
Specifically, SplitEditor::splitLiveThroughBlock() supports switching
between different register intervals in a block.
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RAGreedy::tryAssign will now evict interference from the preferred
register even when another register is free.
To support this, add the EvictionCost struct that counts how many hints
are broken by an eviction. We don't want to break one hint just to
satisfy another.
Rename canEvict to shouldEvict, and add the first bit of eviction policy
that doesn't depend on spill weights: Always make room in the preferred
register as long as the evictees can be split and aren't already
assigned to their preferred register.
Also make the CSR avoidance more accurate. When looking for a cheaper
register it is OK to use a new volatile register. Only CSR aliases that
have never been used before should be avoided.
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hasPredecessorHelper function allows predecessors to be cached to speed up
repeated invocations. This fixes PR10186.
X.isPredecessorOf(Y) now just calls Y.hasPredecessor(X)
Y.hasPredecessor(X) calls Y.hasPredecessorHelper(X, Visited, Worklist) with
empty Visited and Worklist sets (i.e. no caching over invocations).
Y.hasPredecessorHelper(X, Visited, Worklist) caches search state in Visited
and Worklist to speed up repeated calls. The Visited set is searched for X
before going to the worklist to further search the DAG if necessary.
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Add a MI->emitError() method that the backend can use to report errors
related to inline assembly. Call it from X86FloatingPoint.cpp when the
constraints are wrong.
This enables proper clang diagnostics from the backend:
$ clang -c pr30848.c
pr30848.c:5:12: error: Inline asm output regs must be last on the x87 stack
__asm__ ("" : "=u" (d)); /* { dg-error "output regs" } */
^
1 error generated.
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sink them into MC layer.
- Added MCInstrInfo, which captures the tablegen generated static data. Chang
TargetInstrInfo so it's based off MCInstrInfo.
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BranchProbabilityInfo (expect setEdgeWeight which is not available here).
Branch Weights are kept in MachineBasicBlocks. To turn off this analysis
set -use-mbpi=false.
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suffix (e.g. .xdata$myfunc). The suffix part isn't implemented yet, but
I'll get to it in the next patch.
Fix up all callers of the affected functions. Make them pass said suffix to
the function.
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When instructions are deleted, they leave tombstone SlotIndex entries.
The isZeroLength method should ignore these null indexes.
This causes RABasic to sometimes spill a callee-saved register in the
abi-isel.ll test, so don't run that test with -regalloc=basic. Prioritizing
register allocation according to spill weight can cause more registers to be
used.
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markers. In some cases a register def is dead on one path, but not on
another.
This is passing Clang self-hosting.
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this clang will use .debug_frame in, for example,
clang -g -c -m32 test.c
This matches gcc's behaviour. It looks like .debug_frame is a bit bigger
than .eh_frame, but has the big advantage of not being allocated.
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This makes a difference if a live interval is referring to a deleted
instruction. It can be important to insert an instruction before or after a
deleted instruction to avoid interference.
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This could happen when trying to use a value that had been eliminated after dead
code elimination and folding loads.
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give it a bit more responsibility. Also implement it for MachO.
If hacked to use cfi, 32 bit MachO will produce
.cfi_personality 155, L___gxx_personality_v0$non_lazy_ptr
and 64 bit will produce
.cfi_presonality ___gxx_personality_v0
The general idea is that .cfi_personality gets passed the final symbol. It is
up to codegen to produce it if using indirect representation (like 32 bit
MachO), but it is up to MC to decide which relocations to create.
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more callee-saved registers and introduce copies. Only allows it if scheduling
a node above calls would end up lessen register pressure.
Call operands also has added ABI restrictions for register allocation, so be
extra careful with hoisting them above calls.
rdar://9329627
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This has two effects: 1. We never inflate to a larger register class than what
the sub-target can handle. 2. Completely unconstrained virtual registers get the
largest possible register class.
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fix bugs exposed by the gcc dejagnu testsuite:
1. The load may actually be used by a dead instruction, which
would cause an assert.
2. The load may not be used by the current chain of instructions,
and we could move it past a side-effecting instruction. Change
how we process uses to define the problem away.
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The basic issue here is that bottom-up isel is matching the branch
and compare, and was failing to fold the load into the branch/compare
combo. Fixing this (by allowing folding into any instruction of a
sequence that is selected) allows us to produce things like:
cmpb $0, 52(%rax)
je LBB4_2
instead of:
movb 52(%rax), %cl
cmpb $0, %cl
je LBB4_2
This makes the generated -O0 code run a bit faster, but also speeds up
compile time by putting less pressure on the register allocator and
generating less code.
This was one of the biggest classes of missing load folding. Implementing
this shrinks 176.gcc's c-decl.s (as a random example) by about 4% in (verbose-asm)
line count.
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Change ELF systems to use CFI for producing the EH tables. This reduces the
size of the clang binary in Debug builds from 690MB to 679MB.
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This is done by pushing physical register definitions close to their
use, which happens to handle flag definitions if they're not glued to
the branch. This seems to be generally a good thing though, so I
didn't need to add a target hook yet.
The primary motivation is to generate code closer to what people
expect and rule out missed opportunity from enabling macro-op
fusion. As a side benefit, we get several 2-5% gains on x86
benchmarks. There is one regression:
SingleSource/Benchmarks/Shootout/lists slows down be -10%. But this is
an independent scheduler bug that will be tracked separately.
See rdar://problem/9283108.
Incidentally, pre-RA scheduling is only half the solution. Fixing the
later passes is tracked by:
<rdar://problem/8932804> [pre-RA-sched] on x86, attempt to schedule CMP/TEST adjacent with condition jump
Fixes:
<rdar://problem/9262453> Scheduler unnecessary break of cmp/jump fusion
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It is common for large live ranges to have few basic blocks with register uses
and many live-through blocks without any uses. This approach grows the Hopfield
network incrementally around the use blocks, completely avoiding checking
interference for some through blocks.
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induction variable. The preRA scheduler is unaware of induction vars,
so we look for potential "virtual register cycles" instead.
Fixes <rdar://problem/8946719> Bad scheduling prevents coalescing
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This allows us to always keep the smaller slot for an instruction which is what
we want when a register has early clobber defines.
Drop the UsingInstrs set and the UsingBlocks map. They are no longer needed.
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inlined path for the common case.
Most basic blocks don't contain a call that may throw, so the last split point
os simply the first terminator.
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Correctly terminate the range of register DBG_VALUEs when the register is
clobbered or when the basic block ends.
The code is now ready to deal with variables that are sometimes in a register
and sometimes on the stack. We just need to teach emitDebugLoc to say 'stack
slot'.
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I have convinced myself that it can only happen when a phi value dies. When it
happens, allocate new virtual registers for the components.
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Initially, slot indexes are quad-spaced. There is room for inserting up to 3
new instructions between the original instructions.
When we run out of indexes between two instructions, renumber locally using
double-spaced indexes. The original quad-spacing means that we catch up quickly,
and we only have to renumber a handful of instructions to get a monotonic
sequence. This is much faster than renumbering the whole function as we did
before.
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it. It's been assumed up til now that it would be in its immediate
successor. However, this isn't necessarily the case. It could be in one of its
successor's successors.
Modify the code to more thoroughly check for an 'eh.selector' call in
successors. It only looks at a successor if we get there as a result of an
unconditional branch.
Testcase ObjC/exceptions-4.m in r126968.
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This is much faster than using a pointer to a ManagedStatic object accessed with
a function call. The greedy register allocator is 5% faster overall just from
the SlotIndex default constructor savings.
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The SlotIndex created by the default construction does not represent a position
in the function, and it doesn't make sense to compare it to other indexes.
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This method could probably be used by LiveIntervalAnalysis::shrinkToUses, and
now it can use extendIntervalEndTo() which coalesces ranges.
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registers at phis. This enables us to eliminate a lot of pointless zexts during
the DAGCombine phase. This fixes <rdar://problem/8760114>.
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share entries. Add a DenseSet to MachineConstantPool for the MachineCPVs that
it owns.
This will hopefully fix the MC/ARM/elf-reloc-01.ll failure on the leaks bots.
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at phis. This enables us to eliminate a lot of pointless zexts during the DAGCombine
phase. This fixes <rdar://problem/8760114>.
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In other words, do not keep track of argument's location. The debugger (gdb) is not prepared to see line table entries for arguments. For the debugger, "second" line table entry marks beginning of function body.
This requires some coordination with debugger to get this working.
- The debugger needs to be aware of prolog_end attribute attached with line table entries.
- The compiler needs to accurately mark prolog_end in line table entries (at -O0 and at -O1+)
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Simplify the spill weight calculation a bit by bypassing
getApproximateInstructionCount() and using LiveInterval::getSize() directly.
This changes the computed spill weights, but only by a constant factor in each
function. It should not affect how spill weights compare against each other, and
so it shouldn't affect code generation.
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generating i8 shift amounts for things like i1024 types. Add
an assert in getNode to prevent this from occuring in the future,
fix the buggy transformation, revert my previous patch, and
document this gotcha in ISDOpcodes.h
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This is a lot easier than trying to get kill flags right during live range
splitting and rematerialization.
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After uses of a live range are removed, recompute the live range to only cover
the remaining uses. This is necessary after rematerializing the value before
some (but not all) uses.
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A live range cannot be split everywhere in a basic block. A split must go before
the first terminator, and if the variable is live into a landing pad, the split
must happen before the call that can throw.
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precisely track pressure on a selection DAG, but we can at least keep
it balanced. This design accounts for various interesting aspects of
selection DAGS: register and subregister copies, glued nodes, dead
nodes, unused registers, etc.
Added SUnit::NumRegDefsLeft and ScheduleDAGSDNodes::RegDefIter.
Note: I disabled PrescheduleNodesWithMultipleUses when register
pressure is enabled, based on no evidence other than I don't think it
makes sense to have both enabled.
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The greedy register allocator revealed some problems with the value mapping in
SplitKit. We would sometimes start mapping values before all defs were known,
and that could change a value from a simple 1-1 mapping to a multi-def mapping
that requires ssa update.
The new approach collects all defs and register assignments first without
filling in any live intervals. Only when finish() is called, do we compute
liveness and mapped values. At this time we know with certainty which values map
to multiple values in a split range.
This also has the advantage that we can compute live ranges based on the
remaining uses after rematerializing at split points.
The current implementation has many opportunities for compile time optimization.
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default implementation for x86, going through the stack in a similr
fashion to how the codegen implements BUILD_VECTOR. Eventually this
will get matched to VINSERTF128 if AVX is available.
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flags. They are still not enable in this revision.
Added TargetInstrInfo::isZeroCost() to fix a fundamental problem with
the scheduler's model of operand latency in the selection DAG.
Generalized unit tests to work with sched-cycles.
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These functions not longer assert when passed 0, but simply return false instead.
No functional change intended.
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when no virtual registers have been allocated.
It was only used to resize IndexedMaps, so provide an IndexedMap::resize()
method such that
Map.grow(MRI.getLastVirtReg());
can be replaced with the simpler
Map.resize(MRI.getNumVirtRegs());
This works correctly when no virtuals are allocated, and it bypasses the to/from
index conversions.
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physical register numbers.
This makes the hack used in LiveInterval official, and lets LiveInterval be
oblivious of stack slots.
The isPhysicalRegister() and isVirtualRegister() predicates don't know about
this, so when a variable may contain a stack slot, isStackSlot() should always
be tested first.
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of using a Location class with the same information.
When making a copy of a MachineOperand that was already stored in a
MachineInstr, it is necessary to clear the parent pointer on the copy. Otherwise
the register use-def lists become inconsistent.
Add MachineOperand::clearParent() to do that. An alternative would be a custom
MachineOperand copy constructor that cleared ParentMI. I didn't want to do that
because of the performance impact.
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Provide MRI::getNumVirtRegs() and TRI::index2VirtReg() functions to allow
iteration over virtual registers without depending on the representation of
virtual register numbers.
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Instead encode llvm IR level property "HasSideEffects" in an operand (shared
with IsAlignStack). Added MachineInstrs::hasUnmodeledSideEffects() to check
the operand when the instruction is an INLINEASM.
This allows memory instructions to be moved around INLINEASM instructions.
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We were never generating any of these nodes with variable indices, and there
was one legalizer function asserting on a non-constant index. If we ever have
a need to support variable indices, we can add this back again.
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This pass precomputes CFG block frequency information that can be used by the
register allocator to find optimal spill code placement.
Given an interference pattern, placeSpills() will compute which basic blocks
should have the current variable enter or exit in a register, and which blocks
prefer the stack.
The algorithm is ready to consume block frequencies from profiling data, but for
now it gets by with the static estimates used for spill weights.
This is a work in progress and still not hooked up to RegAllocGreedy.
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The analysis will be needed by both the greedy register allocator and the
X86FloatingPoint pass. It only needs to be computed once when the CFG doesn't
change.
This pass is very fast, usually showing up as 0.0% wall time.
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DAG scheduling during isel. Most new functionality is currently
guarded by -enable-sched-cycles and -enable-sched-hazard.
Added InstrItineraryData::IssueWidth field, currently derived from
ARM itineraries, but could be initialized differently on other targets.
Added ScheduleHazardRecognizer::MaxLookAhead to indicate whether it is
active, and if so how many cycles of state it holds.
Added SchedulingPriorityQueue::HasReadyFilter to allowing gating entry
into the scheduler's available queue.
ScoreboardHazardRecognizer now accesses the ScheduleDAG in order to
get information about it's SUnits, provides RecedeCycle for bottom-up
scheduling, correctly computes scoreboard depth, tracks IssueCount, and
considers potential stall cycles when checking for hazards.
ScheduleDAGRRList now models machine cycles and hazards (under
flags). It tracks MinAvailableCycle, drives the hazard recognizer and
priority queue's ready filter, manages a new PendingQueue, properly
accounts for stall cycles, etc.
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createMachineVerifierPass and MachineFunction::verify.
The banner is printed before the machine code dump, just like the printer pass.
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The heuristics split around the largest loop where the current register may be
allocated without interference.
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This is a three-way interval list intersection between a virtual register, a
live interval union, and a loop. It will be used to identify interference-free
loops for live range splitting.
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A MachineLoopRange contains the intervals of slot indexes covered by the blocks
in a loop. This representation of the loop blocks is more efficient to compare
against interfering registers during register coalescing.
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both forward and backward scheduling. Rename it to
ScoreboardHazardRecognizer (Scoreboard is one word). Remove integer
division from the scoreboard's critical path.
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This new register allocator is initially identical to RegAllocBasic, but it will
receive all of the tricks that RegAllocBasic won't get.
RegAllocGreedy will eventually replace linear scan.
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Scan the MachineFunction for DBG_VALUE instructions, and replace them with a
data structure similar to LiveIntervals. The live range of a DBG_VALUE is
determined by propagating it down the dominator tree until a new DBG_VALUE is
found. When a DBG_VALUE lives in a register, its live range is confined to the
live range of the register's value.
LiveDebugVariables runs before coalescing, so DBG_VALUEs are not artificially
extended when registers are joined.
The missing half will recreate DBG_VALUE instructions from the intervals when
register allocation is complete.
The pass is disabled by default. It can be enabled with the temporary command
line option -live-debug-variables.
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legalization time. Since at legalization time there is no mapping from
SDNode back to the corresponding LLVM instruction and the return
SDNode is target specific, this requires a target hook to check for
eligibility. Only x86 and ARM support this form of sibcall optimization
right now.
rdar://8707777
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so don't claim they are. They are allocated using DAG.getNode, so attempts
to access MemSDNode fields results in reading off the end of the allocated
memory. This fixes crashes with "llc -debug" due to debug code trying to
print MemSDNode fields for these barrier nodes (since the crashes are not
deterministic, use valgrind to see this). Add some nasty checking to try
to catch this kind of thing in the future.
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easier to debug, and to avoid complications when the CFG changes
in the middle of the instruction selection process.
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since it is trivial and will be shared between ppc and x86.
This substantially simplifies the X86 backend also.
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This is the first small step towards using closed intervals for liveness instead
of the half-open intervals we're using now.
We want to be able to distinguish between a SlotIndex that represents a variable
being live-out of a basic block, and an index representing a variable live-in to
its successor.
That requires two separate indexes between blocks. One for live-outs and one for
live-ins.
With this change, getMBBEndIdx(MBB).getPrevSlot() becomes stable so it stays
greater than any instructions inserted at the end of MBB.
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benchmarks hitting an assertion.
Adds LiveIntervalUnion::collectInterferingVRegs.
Fixes "late spilling" by checking for any unspillable live vregs among
all physReg aliases.
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and as such can be represented by an MVT - the more complicated
EVT is not needed. Use MVT for ValVT everywhere.
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with a SimpleValueType, while an EVT supports equality and
inequality comparisons with SimpleValueType.
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value type, so there is no point in passing it around using
an EVT. Use the simpler MVT everywhere. Rather than trying
to propagate this information maximally in all the code that
using the calling convention stuff, I chose to do a mainly
low impact change instead.
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1. Fix pre-ra scheduler so it doesn't try to push instructions above calls to
"optimize for latency". Call instructions don't have the right latency and
this is more likely to use introduce spills.
2. Fix if-converter cost function. For ARM, it should use instruction latencies,
not # of micro-ops since multi-latency instructions is completely executed
even when the predicate is false. Also, some instruction will be "slower"
when they are predicated due to the register def becoming implicit input.
rdar://8598427
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memory, so a MachineMemOperand is useful (not propagated
into the MachineInstr yet). No functional change except
for dump output.
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framework. It's purpose is not to improve register allocation per se,
but to make it easier to develop powerful live range splitting. I call
it the basic allocator because it is as simple as a global allocator
can be but provides the building blocks for sophisticated register
allocation with live range splitting.
A minimal implementation is provided that trivially spills whenever it
runs out of registers. I'm checking in now to get high-level design
and style feedback. I've only done minimal testing. The next step is
implementing a "greedy" allocation algorithm that does some register
reassignment and makes better splitting decisions.
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setup they require. Use this for ARM/Darwin to rematerialize the base
pointer from the frame pointer when required. rdar://8564268
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Pull an unsigned out of the Contents union such that it has the same size as two
pointers and no padding.
Arrange members such that the Contents union and all pointers can be 8-byte
aligned without padding.
This speeds up code generation by 0.8% on a 64-bit host. 32-bit hosts should be
unaffected.
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must be called in the pass's constructor. This function uses static dependency declarations to recursively initialize
the pass's dependencies.
Clients that only create passes through the createFooPass() APIs will require no changes. Clients that want to use the
CommandLine options for passes will need to manually call the appropriate initialization functions in PassInitialization.h
before parsing commandline arguments.
I have tested this with all standard configurations of clang and llvm-gcc on Darwin. It is possible that there are problems
with the static dependencies that will only be visible with non-standard options. If you encounter any crash in pass
registration/creation, please send the testcase to me directly.
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connected components. These components should be allocated different virtual
registers because there is no reason for them to be allocated together.
Add the ConnectedVNInfoEqClasses class to calculate the connected components,
and move values to new LiveIntervals.
Use it from SplitKit::rewrite by creating new virtual registers for the
components.
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This function is intended to be used when inserting a machine instruction that
trivially restricts the legal registers, like LEA requiring a GR32_NOSP
argument.
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LiveInterval::MergeValueNumberInto instead of trying to extend LiveRanges and
getting it wrong.
This fixed PR8249 where a valno with a multi-segment live range was defined by
an identity copy created by RemoveCopyByCommutingDef. Some of the live
segments disappeared.
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