llvm-project/llvm/lib/CodeGen
Peter Collingbourne d799d28540 FastISel: Remove unused/un-overridden entry points. NFCI.
llvm-svn: 283366
2016-10-05 19:25:20 +00:00
..
AsmPrinter Improve DEBUG_VALUE assembly comments for spilled bitpieces 2016-10-05 18:36:02 +00:00
GlobalISel [RegisterBankInfo] Change the default mapping for Copy and PHI. 2016-09-29 19:51:46 +00:00
MIRParser [MIRParser] Delete dead code. NFCI. 2016-09-21 18:26:08 +00:00
SelectionDAG FastISel: Remove unused/un-overridden entry points. NFCI. 2016-10-05 19:25:20 +00:00
AggressiveAntiDepBreaker.cpp MachineFunction: Return reference for getFrameInfo(); NFC 2016-07-28 18:40:00 +00:00
AggressiveAntiDepBreaker.h CodeGen: Use MachineInstr& in AntiDepBreaker API, NFC 2016-02-27 19:33:37 +00:00
AllocationOrder.cpp Use the range variant of find instead of unpacking begin/end 2016-08-11 22:21:41 +00:00
AllocationOrder.h Use the range variant of find instead of unpacking begin/end 2016-08-11 22:21:41 +00:00
Analysis.cpp [CGP] Be less conservative about tail-duplicating a ret to allow tail calls 2016-09-08 00:48:37 +00:00
AntiDepBreaker.h CodeGen: Use MachineInstr& in AntiDepBreaker API, NFC 2016-02-27 19:33:37 +00:00
AtomicExpandPass.cpp Support expanding partial-word cmpxchg to full-word cmpxchg in AtomicExpandPass. 2016-06-17 18:11:48 +00:00
BasicTargetTransformInfo.cpp
BranchFolding.cpp BranchFolder: Fix invalid undef flags after merge. 2016-09-20 01:14:42 +00:00
BranchFolding.h Branch Folding: Accept explicit threshold for tail merge size. 2016-08-18 18:57:29 +00:00
BuiltinGCs.cpp [GC] Consolidate all built in GCs into a single file [NFC] 2016-01-19 03:57:18 +00:00
CMakeLists.txt Add a counter-function insertion pass 2016-09-01 09:42:39 +00:00
CalcSpillWeights.cpp CodeGen: Use MachineInstr& in TargetInstrInfo, NFC 2016-06-30 00:01:54 +00:00
CallingConvLower.cpp CodeGen: Factor out code for tail call result compatibility check; NFC 2016-03-30 22:46:04 +00:00
CodeGen.cpp Add a counter-function insertion pass 2016-09-01 09:42:39 +00:00
CodeGenPrepare.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
CountingFunctionInserter.cpp Add a counter-function insertion pass 2016-09-01 09:42:39 +00:00
CriticalAntiDepBreaker.cpp MachineFunction: Return reference for getFrameInfo(); NFC 2016-07-28 18:40:00 +00:00
CriticalAntiDepBreaker.h [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
DFAPacketizer.cpp [Packetizer] Add debugging code to stop packetization after N instructions 2016-08-19 21:12:52 +00:00
DeadMachineInstructionElim.cpp CodeGen: Give MachineBasicBlock::reverse_iterator a handle to the current MI 2016-09-11 18:51:28 +00:00
DetectDeadLanes.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
DwarfEHPrepare.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
EarlyIfConversion.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
EdgeBundles.cpp Fix some Clang-tidy modernize-use-using and Include What You Use warnings; other minor fixes. 2016-08-25 00:45:04 +00:00
ExecutionDepsFix.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
ExpandISelPseudos.cpp CodeGen: Use MachineInstr& in ExpandISelPseudos, NFC 2016-06-30 23:09:39 +00:00
ExpandPostRAPseudos.cpp ExpandPostRAPseudos should transfer implicit uses, not only implicit defs 2016-07-15 22:31:14 +00:00
FaultMaps.cpp
FuncletLayout.cpp MachineFunctionProperties/MIRParser: Rename AllVRegsAllocated->NoVRegs, compute it 2016-08-25 01:27:13 +00:00
GCMetadata.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
GCMetadataPrinter.cpp Reapply r276973 "Adjust Registry interface to not require plugins to export a registry" 2016-08-05 11:01:08 +00:00
GCRootLowering.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
GCStrategy.cpp Reapply r276973 "Adjust Registry interface to not require plugins to export a registry" 2016-08-05 11:01:08 +00:00
GlobalMerge.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
IfConversion.cpp IfConversion: Add implicit uses for redefined regs with live subregisters 2016-09-28 20:07:41 +00:00
ImplicitNullChecks.cpp Finish renaming remaining analyzeBranch functions 2016-09-14 20:43:16 +00:00
InlineSpiller.cpp Place the lowered phi instruction(s) before the DEBUG_VALUE entry 2016-09-16 14:07:29 +00:00
InterferenceCache.cpp
InterferenceCache.h
InterleavedAccessPass.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
IntrinsicLowering.cpp
LLVMBuild.txt Include ProfileData as CodeGen's required library. 2016-02-22 22:54:14 +00:00
LLVMTargetMachine.cpp llc: Add -start-before/-stop-before options 2016-09-23 21:46:02 +00:00
LatencyPriorityQueue.cpp Use the range variant of find instead of unpacking begin/end 2016-08-11 22:21:41 +00:00
LexicalScopes.cpp Rewrite loops to use range-based for. (NFC) 2016-09-28 17:31:17 +00:00
LiveDebugValues.cpp Teach LiveDebugValues about lexical scopes. 2016-09-28 17:51:14 +00:00
LiveDebugVariables.cpp Remove dead code from LiveDebugVariables.cpp (NFC) 2016-09-28 21:34:23 +00:00
LiveDebugVariables.h [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
LiveInterval.cpp Create subranges for new intervals resulting from live interval splitting 2016-08-24 13:37:55 +00:00
LiveIntervalAnalysis.cpp Do not consider subreg defs as reads when computing subrange liveness 2016-09-02 19:48:55 +00:00
LiveIntervalUnion.cpp Use the range variant of find instead of unpacking begin/end 2016-08-11 22:21:41 +00:00
LivePhysRegs.cpp MachineFunction: Return reference for getFrameInfo(); NFC 2016-07-28 18:40:00 +00:00
LiveRangeCalc.cpp LiveRangeCalc: Fix reporting of invalid vreg usage in liveness calculation 2016-09-19 16:49:45 +00:00
LiveRangeCalc.h Do not consider subreg defs as reads when computing subrange liveness 2016-09-02 19:48:55 +00:00
LiveRangeEdit.cpp Create subranges for new intervals resulting from live interval splitting 2016-08-24 13:37:55 +00:00
LiveRangeUtils.h CodeGen: Refactor renameDisconnectedComponents() as a pass 2016-05-31 22:38:06 +00:00
LiveRegMatrix.cpp Move helpers into anonymous namespaces. NFC. 2016-08-06 11:13:10 +00:00
LiveStackAnalysis.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
LiveVariables.cpp CodeGen: Use MachineInstr& in LiveVariables API, NFC 2016-07-01 01:51:32 +00:00
LocalStackSlotAllocation.cpp MachineFunction: Return reference for getFrameInfo(); NFC 2016-07-28 18:40:00 +00:00
LowLevelType.cpp GlobalISel: produce correct code for signext/zeroext ABI flags. 2016-09-21 12:57:45 +00:00
LowerEmuTLS.cpp Re-commit optimization bisect support (r267022) without new pass manager support. 2016-04-22 22:06:11 +00:00
MIRPrinter.cpp GlobalISel: disambiguate types when printing MIR 2016-09-12 11:20:10 +00:00
MIRPrinter.h
MIRPrintingPass.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
MachineBasicBlock.cpp Use StringRef instead of raw pointers in MCAsmInfo/MCInstrInfo APIs (NFC) 2016-10-01 06:46:33 +00:00
MachineBlockFrequencyInfo.cpp s/static inline/static/ for headers I have changed in r279475. NFC. 2016-08-31 16:48:13 +00:00
MachineBlockPlacement.cpp Revert "Codegen: Tail-duplicate during placement." 2016-10-05 01:39:29 +00:00
MachineBranchProbabilityInfo.cpp Use the range variant of find/find_if instead of unpacking begin/end 2016-08-12 03:55:06 +00:00
MachineCSE.cpp [CodeGen] Rename MachineInstr::isInvariantLoad to isDereferenceableInvariantLoad. NFC 2016-09-10 01:03:20 +00:00
MachineCombiner.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
MachineCopyPropagation.cpp MachineFunctionProperties/MIRParser: Rename AllVRegsAllocated->NoVRegs, compute it 2016-08-25 01:27:13 +00:00
MachineDominanceFrontier.cpp
MachineDominators.cpp [MDT] Always verify machine dominfo if expensive checking is enabled. 2016-06-24 17:15:04 +00:00
MachineFunction.cpp Use StringRef in Datalayout API (NFC) 2016-10-01 05:57:55 +00:00
MachineFunctionPass.cpp [MFProperties][NFC] Rename clear into reset to match BitVector naming. 2016-08-26 22:09:08 +00:00
MachineFunctionPrinterPass.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
MachineInstr.cpp AMDGPU: Support commuting a FrameIndex operand 2016-09-13 19:03:12 +00:00
MachineInstrBundle.cpp Move instances of std::function. 2016-06-12 16:13:55 +00:00
MachineLICM.cpp [CodeGen] Rename MachineInstr::isInvariantLoad to isDereferenceableInvariantLoad. NFC 2016-09-10 01:03:20 +00:00
MachineLoopInfo.cpp MachineLoop: add methods findLoopControlBlock and findLoopPreheader 2016-08-15 08:22:42 +00:00
MachineModuleInfo.cpp CodeGen: Remove MachineFunctionAnalysis => Enable (Machine)ModulePasses 2016-08-24 01:52:46 +00:00
MachineModuleInfoImpls.cpp
MachinePassRegistry.cpp
MachinePipeliner.cpp Finish renaming remaining analyzeBranch functions 2016-09-14 20:43:16 +00:00
MachinePostDominators.cpp
MachineRegionInfo.cpp Introduce DominanceFrontierAnalysis to the new PassManager to compute DominanceFrontier. NFC 2016-02-25 17:54:15 +00:00
MachineRegisterInfo.cpp [TargetRegisterInfo, AArch64] Add target hook for isConstantPhysReg(). 2016-09-27 22:17:27 +00:00
MachineSSAUpdater.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
MachineScheduler.cpp MachineScheduler: Slightly simplify release node 2016-09-22 21:39:56 +00:00
MachineSink.cpp Fix some Clang-tidy modernize-use-using and Include What You Use warnings; other minor fixes. 2016-08-25 00:45:04 +00:00
MachineTraceMetrics.cpp [ADT] Change PostOrderIterator to use NodeRef. NFC. 2016-08-15 21:52:54 +00:00
MachineVerifier.cpp GlobalISel: remove "unsized" LLT 2016-09-15 10:09:59 +00:00
OptimizePHIs.cpp CodeGen: Avoid dereferencing end() in OptimizePHIs::OptimizeBB 2016-08-17 00:43:59 +00:00
PHIElimination.cpp MachineFunction: Introduce NoPHIs property 2016-08-23 21:19:49 +00:00
PHIEliminationUtils.cpp Place the lowered phi instruction(s) before the DEBUG_VALUE entry 2016-09-16 14:07:29 +00:00
PHIEliminationUtils.h
ParallelCG.cpp Apply another batch of fixes from clang-tidy's performance-unnecessary-value-param. 2016-06-17 20:41:14 +00:00
PatchableFunction.cpp MachineFunctionProperties/MIRParser: Rename AllVRegsAllocated->NoVRegs, compute it 2016-08-25 01:27:13 +00:00
PeepholeOptimizer.cpp Fix some Clang-tidy modernize-use-using and Include What You Use warnings; other minor fixes. 2016-08-25 00:45:04 +00:00
PostRAHazardRecognizer.cpp CodeGen: Use MachineInstr& in PostRAHazardRecognizer, NFC 2016-07-01 00:50:29 +00:00
PostRASchedulerList.cpp MachineFunctionProperties/MIRParser: Rename AllVRegsAllocated->NoVRegs, compute it 2016-08-25 01:27:13 +00:00
PreISelIntrinsicLowering.cpp [PM] Port PreISelIntrinsicLowering to the new PM 2016-06-24 20:13:42 +00:00
ProcessImplicitDefs.cpp Revert "CodeGen: MachineInstr::getIterator() => getInstrIterator(), NFC" 2016-02-22 20:49:58 +00:00
PrologEpilogInserter.cpp MachineFunctionProperties/MIRParser: Rename AllVRegsAllocated->NoVRegs, compute it 2016-08-25 01:27:13 +00:00
PseudoSourceValue.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
README.txt
RegAllocBase.cpp Create subranges for new intervals resulting from live interval splitting 2016-08-24 13:37:55 +00:00
RegAllocBase.h Recommit r265547, and r265610,r265639,r265657 on top of it, plus 2016-04-13 03:08:27 +00:00
RegAllocBasic.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
RegAllocFast.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
RegAllocGreedy.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
RegAllocPBQP.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
RegUsageInfoCollector.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
RegUsageInfoPropagate.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
RegisterClassInfo.cpp
RegisterCoalescer.cpp Missed a semicolon in r279835 2016-08-26 16:50:57 +00:00
RegisterCoalescer.h
RegisterPressure.cpp Use the range variant of find/find_if instead of unpacking begin/end 2016-08-12 03:55:06 +00:00
RegisterScavenging.cpp [RegisterScavenger] Remove aliasing registers of operands from the candidate set 2016-09-06 10:10:21 +00:00
RegisterUsageInfo.cpp Move helpers into anonymous namespaces. NFC. 2016-08-06 11:13:10 +00:00
RenameIndependentSubregs.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
ResetMachineFunctionPass.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
SafeStack.cpp Revert r283248. It caused failures in the hexagon buildbots. 2016-10-04 20:57:19 +00:00
SafeStackColoring.cpp [safestack] Fix assertion failure in stack coloring. 2016-09-16 22:04:10 +00:00
SafeStackColoring.h StackColoring for SafeStack. 2016-06-29 20:37:43 +00:00
SafeStackLayout.cpp [safestack] Layout large allocas first to reduce fragmentation. 2016-08-02 23:21:30 +00:00
SafeStackLayout.h StackColoring for SafeStack. 2016-06-29 20:37:43 +00:00
ScheduleDAG.cpp ScheduleDAG: Match enum names when printing sdep kinds 2016-09-23 18:28:31 +00:00
ScheduleDAGInstrs.cpp Fix machine operand traversal in ScheduleDAGInstrs::fixupKills 2016-10-05 13:15:06 +00:00
ScheduleDAGPrinter.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
ScoreboardHazardRecognizer.cpp Replace "fallthrough" comments with LLVM_FALLTHROUGH 2016-08-17 05:10:15 +00:00
ShadowStackGCLowering.cpp [GC] Consolidate all built in GCs into a single file [NFC] 2016-01-19 03:57:18 +00:00
ShrinkWrap.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
SjLjEHPrepare.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
SlotIndexes.cpp CodeGen: Use MachineInstr& in SlotIndexes.cpp, NFC 2016-07-01 15:08:52 +00:00
SpillPlacement.cpp Reapply r263460: [SpillPlacement] Fix a quadratic behavior in spill placement. 2016-05-19 22:40:37 +00:00
SpillPlacement.h Reapply r263460: [SpillPlacement] Fix a quadratic behavior in spill placement. 2016-05-19 22:40:37 +00:00
Spiller.h Recommit r265547, and r265610,r265639,r265657 on top of it, plus 2016-04-13 03:08:27 +00:00
SplitKit.cpp Place the lowered phi instruction(s) before the DEBUG_VALUE entry 2016-09-16 14:07:29 +00:00
SplitKit.h Create subranges for new intervals resulting from live interval splitting 2016-08-24 13:37:55 +00:00
StackColoring.cpp MachineFunction: Return reference for getFrameInfo(); NFC 2016-07-28 18:40:00 +00:00
StackMapLivenessAnalysis.cpp MachineFunctionProperties/MIRParser: Rename AllVRegsAllocated->NoVRegs, compute it 2016-08-25 01:27:13 +00:00
StackMaps.cpp [Stackmap] Added callsite counts to emitted function information. 2016-09-14 20:22:03 +00:00
StackProtector.cpp [CodeGen] stop short-circuiting the SSP code for sspstrong. 2016-09-20 21:30:01 +00:00
StackSlotColoring.cpp MachineFunction: Return reference for getFrameInfo(); NFC 2016-07-28 18:40:00 +00:00
TailDuplication.cpp Revert "Codegen: Tail-duplicate during placement." 2016-10-05 01:39:29 +00:00
TailDuplicator.cpp Revert "Codegen: Tail-duplicate during placement." 2016-10-05 01:39:29 +00:00
TargetFrameLoweringImpl.cpp MachineFunction: Return reference for getFrameInfo(); NFC 2016-07-28 18:40:00 +00:00
TargetInstrInfo.cpp Use StringRef instead of raw pointers in MCAsmInfo/MCInstrInfo APIs (NFC) 2016-10-01 06:46:33 +00:00
TargetLoweringBase.cpp [Target] move reciprocal estimate settings from TargetOptions to TargetLowering 2016-10-04 20:46:43 +00:00
TargetLoweringObjectFileImpl.cpp Revert "Remove extra argument used once on 2016-09-20 22:03:28 +00:00
TargetOptionsImpl.cpp MachineFunction: Return reference for getFrameInfo(); NFC 2016-07-28 18:40:00 +00:00
TargetPassConfig.cpp llc: Add -start-before/-stop-before options 2016-09-23 21:46:02 +00:00
TargetRegisterInfo.cpp Use the range variant of find instead of unpacking begin/end 2016-08-11 22:21:41 +00:00
TargetSchedule.cpp TargetSchedule: Do not consider subregister definitions as reads. 2016-08-24 02:32:29 +00:00
TwoAddressInstructionPass.cpp [TwoAddressInstruction] When commuting an instruction don't assume that the destination register is operand 0. Pass it from the caller. 2016-09-11 22:10:42 +00:00
UnreachableBlockElim.cpp [PM] Port UnreachableBlockElim to the new Pass Manager 2016-07-08 03:32:49 +00:00
VirtRegMap.cpp MachineFunctionProperties/MIRParser: Rename AllVRegsAllocated->NoVRegs, compute it 2016-08-25 01:27:13 +00:00
WinEHPrepare.cpp Use StringRef in Pass/PassManager APIs (NFC) 2016-10-01 02:56:57 +00:00
XRayInstrumentation.cpp [XRay] ARM 32-bit no-Thumb support in LLVM 2016-09-19 00:54:35 +00:00

README.txt

//===---------------------------------------------------------------------===//

Common register allocation / spilling problem:

        mul lr, r4, lr
        str lr, [sp, #+52]
        ldr lr, [r1, #+32]
        sxth r3, r3
        ldr r4, [sp, #+52]
        mla r4, r3, lr, r4

can be:

        mul lr, r4, lr
        mov r4, lr
        str lr, [sp, #+52]
        ldr lr, [r1, #+32]
        sxth r3, r3
        mla r4, r3, lr, r4

and then "merge" mul and mov:

        mul r4, r4, lr
        str r4, [sp, #+52]
        ldr lr, [r1, #+32]
        sxth r3, r3
        mla r4, r3, lr, r4

It also increase the likelihood the store may become dead.

//===---------------------------------------------------------------------===//

bb27 ...
        ...
        %reg1037 = ADDri %reg1039, 1
        %reg1038 = ADDrs %reg1032, %reg1039, %NOREG, 10
    Successors according to CFG: 0x8b03bf0 (#5)

bb76 (0x8b03bf0, LLVM BB @0x8b032d0, ID#5):
    Predecessors according to CFG: 0x8b0c5f0 (#3) 0x8b0a7c0 (#4)
        %reg1039 = PHI %reg1070, mbb<bb76.outer,0x8b0c5f0>, %reg1037, mbb<bb27,0x8b0a7c0>

Note ADDri is not a two-address instruction. However, its result %reg1037 is an
operand of the PHI node in bb76 and its operand %reg1039 is the result of the
PHI node. We should treat it as a two-address code and make sure the ADDri is
scheduled after any node that reads %reg1039.

//===---------------------------------------------------------------------===//

Use local info (i.e. register scavenger) to assign it a free register to allow
reuse:
        ldr r3, [sp, #+4]
        add r3, r3, #3
        ldr r2, [sp, #+8]
        add r2, r2, #2
        ldr r1, [sp, #+4]  <==
        add r1, r1, #1
        ldr r0, [sp, #+4]
        add r0, r0, #2

//===---------------------------------------------------------------------===//

LLVM aggressively lift CSE out of loop. Sometimes this can be negative side-
effects:

R1 = X + 4
R2 = X + 7
R3 = X + 15

loop:
load [i + R1]
...
load [i + R2]
...
load [i + R3]

Suppose there is high register pressure, R1, R2, R3, can be spilled. We need
to implement proper re-materialization to handle this:

R1 = X + 4
R2 = X + 7
R3 = X + 15

loop:
R1 = X + 4  @ re-materialized
load [i + R1]
...
R2 = X + 7 @ re-materialized
load [i + R2]
...
R3 = X + 15 @ re-materialized
load [i + R3]

Furthermore, with re-association, we can enable sharing:

R1 = X + 4
R2 = X + 7
R3 = X + 15

loop:
T = i + X
load [T + 4]
...
load [T + 7]
...
load [T + 15]
//===---------------------------------------------------------------------===//

It's not always a good idea to choose rematerialization over spilling. If all
the load / store instructions would be folded then spilling is cheaper because
it won't require new live intervals / registers. See 2003-05-31-LongShifts for
an example.

//===---------------------------------------------------------------------===//

With a copying garbage collector, derived pointers must not be retained across
collector safe points; the collector could move the objects and invalidate the
derived pointer. This is bad enough in the first place, but safe points can
crop up unpredictably. Consider:

        %array = load { i32, [0 x %obj] }** %array_addr
        %nth_el = getelementptr { i32, [0 x %obj] }* %array, i32 0, i32 %n
        %old = load %obj** %nth_el
        %z = div i64 %x, %y
        store %obj* %new, %obj** %nth_el

If the i64 division is lowered to a libcall, then a safe point will (must)
appear for the call site. If a collection occurs, %array and %nth_el no longer
point into the correct object.

The fix for this is to copy address calculations so that dependent pointers
are never live across safe point boundaries. But the loads cannot be copied
like this if there was an intervening store, so may be hard to get right.

Only a concurrent mutator can trigger a collection at the libcall safe point.
So single-threaded programs do not have this requirement, even with a copying
collector. Still, LLVM optimizations would probably undo a front-end's careful
work.

//===---------------------------------------------------------------------===//

The ocaml frametable structure supports liveness information. It would be good
to support it.

//===---------------------------------------------------------------------===//

The FIXME in ComputeCommonTailLength in BranchFolding.cpp needs to be
revisited. The check is there to work around a misuse of directives in inline
assembly.

//===---------------------------------------------------------------------===//

It would be good to detect collector/target compatibility instead of silently
doing the wrong thing.

//===---------------------------------------------------------------------===//

It would be really nice to be able to write patterns in .td files for copies,
which would eliminate a bunch of explicit predicates on them (e.g. no side 
effects).  Once this is in place, it would be even better to have tblgen 
synthesize the various copy insertion/inspection methods in TargetInstrInfo.

//===---------------------------------------------------------------------===//

Stack coloring improvements:

1. Do proper LiveStackAnalysis on all stack objects including those which are
   not spill slots.
2. Reorder objects to fill in gaps between objects.
   e.g. 4, 1, <gap>, 4, 1, 1, 1, <gap>, 4 => 4, 1, 1, 1, 1, 4, 4

//===---------------------------------------------------------------------===//

The scheduler should be able to sort nearby instructions by their address. For
example, in an expanded memset sequence it's not uncommon to see code like this:

  movl $0, 4(%rdi)
  movl $0, 8(%rdi)
  movl $0, 12(%rdi)
  movl $0, 0(%rdi)

Each of the stores is independent, and the scheduler is currently making an
arbitrary decision about the order.

//===---------------------------------------------------------------------===//

Another opportunitiy in this code is that the $0 could be moved to a register:

  movl $0, 4(%rdi)
  movl $0, 8(%rdi)
  movl $0, 12(%rdi)
  movl $0, 0(%rdi)

This would save substantial code size, especially for longer sequences like
this. It would be easy to have a rule telling isel to avoid matching MOV32mi
if the immediate has more than some fixed number of uses. It's more involved
to teach the register allocator how to do late folding to recover from
excessive register pressure.