llvm-project/llvm/lib/CodeGen
Alexey Samsonov dfcaf9c8d8 Rewrite calculateDbgValueHistory to make it (hopefully) more transparent.
This change preserves the original algorithm of generating history
for user variables, but makes it more clear.

High-level description of algorithm:
Scan all the machine basic blocks and machine instructions in the order
they are emitted to the object file. Do the following:
1) If we see a DBG_VALUE instruction, add it to the history of the
corresponding user variable. Keep track of all user variables, whose
locations are described by a register.
2) If we see a regular instruction, look at all the registers it clobbers,
and terminate the location range for all variables described by these registers.
3) At the end of the basic block, terminate location ranges for all
user variables described by some register.

Although this change shouldn't be user-visible (the contents of .debug_loc section
should be the same), it changes some internal assumptions about the set
of instructions used to track the variable locations. Watching the bots.

llvm-svn: 209225
2014-05-20 18:34:54 +00:00
..
AsmPrinter Rewrite calculateDbgValueHistory to make it (hopefully) more transparent. 2014-05-20 18:34:54 +00:00
SelectionDAG Legalizer: Make bswap promotion safe for vectors. 2014-05-20 09:42:31 +00:00
AggressiveAntiDepBreaker.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
AggressiveAntiDepBreaker.h [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-16 04:21:27 +00:00
AllocationOrder.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
AllocationOrder.h Check hint registers for interference only once before evictions 2013-12-05 21:18:40 +00:00
Analysis.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
AntiDepBreaker.h Revert "Give internal classes hidden visibility." 2013-09-11 18:05:11 +00:00
AtomicExpandLoadLinkedPass.cpp [C++] Use 'nullptr'. 2014-04-24 06:44:33 +00:00
BasicTargetTransformInfo.cpp Fix a spelling error 2014-05-08 13:42:57 +00:00
BranchFolding.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
BranchFolding.h Revert "Give internal classes hidden visibility." 2013-09-11 18:05:11 +00:00
CMakeLists.txt Atomics: promote ARM's IR-based atomics pass to CodeGen. 2014-04-17 18:22:47 +00:00
CalcSpillWeights.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
CallingConvLower.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
CodeGen.cpp Atomics: promote ARM's IR-based atomics pass to CodeGen. 2014-04-17 18:22:47 +00:00
CodeGenPrepare.cpp Add missing line breaks to debug output in CodeGenPrepare 2014-05-13 21:54:22 +00:00
CriticalAntiDepBreaker.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
CriticalAntiDepBreaker.h [C++11] Add 'override' keyword to virtual methods that override their base class. 2014-03-07 09:26:03 +00:00
DFAPacketizer.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
DeadMachineInstructionElim.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
DwarfEHPrepare.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
EarlyIfConversion.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
EdgeBundles.cpp Convert several loops over MachineFunction basic blocks to range-based loops 2014-04-30 18:29:51 +00:00
ErlangGC.cpp [C++11] Add 'override' keyword to virtual methods that override their base class. 2014-03-07 09:26:03 +00:00
ExecutionDepsFix.cpp Clean up language and grammar. 2014-05-20 17:11:11 +00:00
ExpandISelPseudos.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
ExpandPostRAPseudos.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
GCMetadata.cpp Use unique_ptr for the result of Registry entries. 2014-04-15 05:53:26 +00:00
GCMetadataPrinter.cpp
GCStrategy.cpp Use unique_ptr to manage ownership of GCFunctionInfos in GCStrategy 2014-04-15 06:07:26 +00:00
IfConversion.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
InlineSpiller.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
InterferenceCache.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
InterferenceCache.h [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-16 04:21:27 +00:00
IntrinsicLowering.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
JITCodeEmitter.cpp
LLVMBuild.txt Prune redundant dependencies in LLVMBuild.txt. 2013-12-11 00:30:57 +00:00
LLVMTargetMachine.cpp Fix typos. 2014-05-19 21:18:47 +00:00
LatencyPriorityQueue.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
LexicalScopes.cpp Recommit r208506: DebugInfo: Include lexical scopes in inlined subroutines. 2014-05-14 01:08:28 +00:00
LiveDebugVariables.cpp This reapplies r207235 with an additional bugfixes caught by the msan 2014-04-25 20:49:25 +00:00
LiveDebugVariables.h [C++11] Add 'override' keyword to virtual methods that override their base class. 2014-03-07 09:26:03 +00:00
LiveInterval.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
LiveIntervalAnalysis.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
LiveIntervalUnion.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
LivePhysRegs.cpp Convert register liveness tracking to work on a sub-register level instead of just register units. 2013-12-14 06:52:56 +00:00
LiveRangeCalc.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
LiveRangeCalc.h [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-16 04:21:27 +00:00
LiveRangeEdit.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
LiveRegMatrix.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
LiveStackAnalysis.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
LiveVariables.cpp Convert more loops to range-based equivalents 2014-04-30 22:17:38 +00:00
LocalStackSlotAllocation.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
MachineBasicBlock.cpp [Modules] Make Support/Debug.h modular. This requires it to not change 2014-04-21 22:55:11 +00:00
MachineBlockFrequencyInfo.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
MachineBlockPlacement.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
MachineBranchProbabilityInfo.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
MachineCSE.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
MachineCodeEmitter.cpp
MachineCopyPropagation.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
MachineDominators.cpp
MachineFunction.cpp Convert several loops over MachineFunction basic blocks to range-based loops 2014-04-30 18:29:51 +00:00
MachineFunctionAnalysis.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
MachineFunctionPass.cpp [stackprotector] Use analysis from the StackProtector pass for stack layout in PEI a nd LocalStackSlot passes. 2013-12-19 03:17:11 +00:00
MachineFunctionPrinterPass.cpp [C++11] Add 'override' keyword to virtual methods that override their base class. 2014-03-07 09:26:03 +00:00
MachineInstr.cpp [BUG][REFACTOR] 2014-05-07 09:51:22 +00:00
MachineInstrBundle.cpp [C++11] Add 'override' keyword to virtual methods that override their base class. 2014-03-07 09:26:03 +00:00
MachineLICM.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
MachineLoopInfo.cpp [C++11] Replace llvm::next and llvm::prior with std::next and std::prev. 2014-03-02 12:27:27 +00:00
MachineModuleInfo.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
MachineModuleInfoImpls.cpp
MachinePassRegistry.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
MachinePostDominators.cpp
MachineRegisterInfo.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
MachineSSAUpdater.cpp [Modules] Make Support/Debug.h modular. This requires it to not change 2014-04-21 22:55:11 +00:00
MachineScheduler.cpp [C++11] Add 'override' keywords and remove 'virtual'. Additionally add 'final' and leave 'virtual' on some methods that are marked virtual without overriding anything and have no obvious overrides themselves. 2014-04-29 07:58:41 +00:00
MachineSink.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
MachineTraceMetrics.cpp Convert more loops to range-based equivalents 2014-04-30 22:17:38 +00:00
MachineVerifier.cpp Convert more loops to range-based equivalents 2014-04-30 22:17:38 +00:00
Makefile
OcamlGC.cpp
OptimizePHIs.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
PHIElimination.cpp Convert more loops to range-based equivalents 2014-04-30 22:17:38 +00:00
PHIEliminationUtils.cpp Switch a number of loops in lib/CodeGen over to range-based for-loops, now that 2014-03-17 19:36:09 +00:00
PHIEliminationUtils.h Fixed another place in CodeGen where we had a typo in our editor C++ filetype declaration. 2013-08-12 20:52:06 +00:00
Passes.cpp verify-di: Implement DebugInfoVerifier 2014-04-15 16:27:38 +00:00
PeepholeOptimizer.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
PostRASchedulerList.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
ProcessImplicitDefs.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
PrologEpilogInserter.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
PrologEpilogInserter.h [C++11] Add 'override' keyword to virtual methods that override their base class. 2014-03-07 09:26:03 +00:00
PseudoSourceValue.cpp Break PseudoSourceValue out of the Value hierarchy. It is now the root of its own tree containing FixedStackPseudoSourceValue (which you can use isa/dyn_cast on) and MipsCallEntry (which you can't). Anything that needs to use either a PseudoSourceValue* and Value* is strongly encouraged to use a MachinePointerInfo instead. 2014-04-15 07:22:52 +00:00
README.txt Correct wrong register in this example, pointed out by Baoshan Pang. 2013-06-07 08:30:55 +00:00
RegAllocBase.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
RegAllocBase.h [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-16 04:21:27 +00:00
RegAllocBasic.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
RegAllocFast.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
RegAllocGreedy.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
RegAllocPBQP.cpp Convert more loops to range-based equivalents 2014-04-30 22:17:38 +00:00
RegisterClassInfo.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
RegisterCoalescer.cpp Convert more loops to range-based equivalents 2014-04-30 22:17:38 +00:00
RegisterCoalescer.h [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-16 04:21:27 +00:00
RegisterPressure.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
RegisterScavenging.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
ScheduleDAG.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
ScheduleDAGInstrs.cpp Fix typos 2014-05-15 01:52:21 +00:00
ScheduleDAGPrinter.cpp Put the functionality for printing a value to a raw_ostream as an 2014-01-09 02:29:41 +00:00
ScoreboardHazardRecognizer.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
ShadowStackGC.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
SjLjEHPrepare.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
SlotIndexes.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
SpillPlacement.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
SpillPlacement.h [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-16 04:21:27 +00:00
Spiller.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
Spiller.h
SplitKit.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
SplitKit.h Clean up language and grammar. 2014-05-20 17:11:11 +00:00
StackColoring.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
StackMapLivenessAnalysis.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
StackMaps.cpp [Stackmaps] Pacify windows buildbot. 2014-05-01 22:39:26 +00:00
StackProtector.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
StackSlotColoring.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
TailDuplication.cpp Convert more loops to range-based equivalents 2014-04-30 22:17:38 +00:00
TargetFrameLoweringImpl.cpp
TargetInstrInfo.cpp [TargetInstrInfo] Fix the implementation of commuteInstruction to match the 2014-05-08 23:12:27 +00:00
TargetLoweringBase.cpp X86TTI: Adjust sdiv cost now that we can lower it on plain SSE2. 2014-04-27 18:47:54 +00:00
TargetLoweringObjectFileImpl.cpp Add comdat key field to llvm.global_ctors and llvm.global_dtors 2014-05-16 20:39:27 +00:00
TargetOptionsImpl.cpp Re-sort all of the includes with ./utils/sort_includes.py so that 2014-01-07 11:48:04 +00:00
TargetRegisterInfo.cpp [C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr. 2014-04-14 00:51:57 +00:00
TargetSchedule.cpp IfConverter: Use TargetSchedule for instruction latencies 2013-09-30 15:28:56 +00:00
TwoAddressInstructionPass.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +00:00
UnreachableBlockElim.cpp [C++11] Add 'override' keyword to virtual methods that override their base class. 2014-03-07 09:26:03 +00:00
VirtRegMap.cpp [Modules] Remove potential ODR violations by sinking the DEBUG_TYPE 2014-04-22 02:02:50 +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.