In some rare cases, the register allocator can spill registers but end up not utilizing registers at all. The fundamental problem is linearscan's backtracking can end up freeing more than one allocated registers. However,  reloads and restores might be folded into uses / defs and freed registers might not be used at all.

VirtRegMap keeps track of allocations so it knows what's not used. As a horrible hack, the stack coloring can color spill slots with *free* registers. That is, it replace reload and spills with copies from and to the free register. It unfold instructions that load and store the spill slot and replace them with register using variants.

Not yet enabled. This is part 1. More coming.

llvm-svn: 70787

llvm-svn: 70524

spillPhysRegAroundRegDefsUses() may have invalidated iterators stored in fixed_ IntervalPtrs. Reset them.

llvm-svn: 70378

Determine allocation 'preference' with right register class. I haven't seen this changing codegen so no test case.

llvm-svn: 70351

This fixes a very subtle bug. vr defined by an implicit_def is allowed overlap with any register since it doesn't actually modify anything. However, if it's used as a two-address use, its live range can be extended and it can be spilled. The spiller must take care not to emit a reload for the vn number that's defined by the implicit_def. This is both a correctness and performance issue.

llvm-svn: 69743

- Find more reloads from SS.

llvm-svn: 69606

Added a linearscan register allocation optimization. When the register allocator spill an interval with multiple uses in the same basic block, it creates a different virtual register for each of the reloads. e.g.

	%reg1498<def> = MOV32rm %reg1024, 1, %reg0, 12, %reg0, Mem:LD(4,4) [sunkaddr39 + 0]
        %reg1506<def> = MOV32rm %reg1024, 1, %reg0, 8, %reg0, Mem:LD(4,4) [sunkaddr42 + 0]
        %reg1486<def> = MOV32rr %reg1506
        %reg1486<def> = XOR32rr %reg1486, %reg1498, %EFLAGS<imp-def,dead>
        %reg1510<def> = MOV32rm %reg1024, 1, %reg0, 4, %reg0, Mem:LD(4,4) [sunkaddr45 + 0]

=>

        %reg1498<def> = MOV32rm %reg2036, 1, %reg0, 12, %reg0, Mem:LD(4,4) [sunkaddr39 + 0]
        %reg1506<def> = MOV32rm %reg2037, 1, %reg0, 8, %reg0, Mem:LD(4,4) [sunkaddr42 + 0]
        %reg1486<def> = MOV32rr %reg1506
        %reg1486<def> = XOR32rr %reg1486, %reg1498, %EFLAGS<imp-def,dead>
        %reg1510<def> = MOV32rm %reg2038, 1, %reg0, 4, %reg0, Mem:LD(4,4) [sunkaddr45 + 0]

From linearscan's point of view, each of reg2036, 2037, and 2038 are separate registers, each is "killed" after a single use. The reloaded register is available and it's often clobbered right away. e.g. In thise case reg1498 is allocated EAX while reg2036 is allocated RAX. This means we end up with multiple reloads from the same stack slot in the same basic block.

Now linearscan recognize there are other reloads from same SS in the same BB. So it'll "downgrade" RAX (and its aliases) after reg2036 is allocated until the next reload (reg2037) is done. This greatly increase the likihood reloads from SS are reused.

This speeds up sha1 from OpenSSL by 5.8%. It is also an across the board win for SPEC2000 and 2006.

llvm-svn: 69585

Fix a bug in spill weight computation. If the alias is a super-register, and the super-register is in the register class we are trying to allocate. Then add the weight to all sub-registers of the super-register even if they are not aliases.                                                                                                  
e.g. allocating for GR32, bh is not used, updating bl spill weight.                                                                                                        
     bl should get the same spill weight otherwise it will be choosen                                                                                              
     as a spill candidate since spilling bh doesn't make ebx available.
This fix PR2866.

llvm-svn: 67574

llvm-svn: 67544

llvm-svn: 66870

Reorganization: Move the Spiller out of VirtRegMap.cpp into its own files.  No (intended) functionality change.

llvm-svn: 66720

llvm-svn: 62600

llvm-svn: 62547

llvm-svn: 61715

- If a def is spilt, remember its spill index to allow its reuse.

llvm-svn: 58375

- Create and update spill slot live intervals.
- Lots of bug fixes.

llvm-svn: 58367

Committing a good chunk of the pre-register allocation live interval splitting pass. It's handling simple cases and appear to do good things. Next: avoid splitting an interval multiple times; renumber registers when possible; record stack slot live intervals for coloring; rematerialize defs when possible.

llvm-svn: 58044

instead of requiring all "short description" strings to begin with
two spaces. This makes these strings less mysterious, and it fixes
some cases where short description strings mistakenly did not
begin with two spaces.

llvm-svn: 57521

llvm-svn: 57259

llvm-svn: 56848

"If a re-materializable instruction has a register
operand, the spiller will change the register operand's
spill weight to HUGE_VAL to avoid it being spilled.
However, if the operand is already in the queue ready
to be spilled, avoid re-materializing it".

llvm-svn: 56837

If a re-materializable instruction has a register operand, the spiller will change the register operand's spill weight to HUGE_VAL to avoid it being spilled. However, if the operand is already in the queue ready to be spilled, avoid re-materializing it.

llvm-svn: 56835

RA problem by expanding the live interval of an
earlyclobber def back one slot.  Remove
overlap-earlyclobber throughout.  Remove 
earlyclobber bits and their handling from
live internals.

llvm-svn: 56539

Check bits for preferred register.

llvm-svn: 56384

Fix PR2808. When regalloc runs out of register, it spill a physical register around the live interval being allocated. Do not continue to try to spill another register, just grab the physical register and move on.

llvm-svn: 56381

have previously been assigned conflicting physreg.

llvm-svn: 56364

and redo as linked list walk.  Logic moved into RA.
Per review feedback.

llvm-svn: 56326

llvm-svn: 56314

with an earlyclobber operand elsewhere.  Propagate
this bit and the earlyclobber bit through SDISel.
Change linear-scan RA not to allocate regs in a way 
that conflicts with an earlyclobber.  See also comments.

llvm-svn: 56290

Fix PR2757. Ignore liveinterval register allocation preference if the preference register is not in the right register class. This can happen due to sub-register coalescing.

llvm-svn: 56006

llvm-svn: 55779

Convert several std::vectors over to SmallVector, and use reserve() as appropriate for cases where std::vector is still used.

llvm-svn: 54820

llvm-svn: 54770

Make the allocation of LiveIntervals explicit, rather than holding them in the r2iMap_ by value.  This will prevent references to them from being invalidated
if the map is changed.

llvm-svn: 54763

to multiply the instruction count by a constant factor in a few places, which
caused the register allocator to require many more iterations.

llvm-svn: 53959

live intervals itself to use an instruction count approximation that is 
not affected by inserting empty indices.

llvm-svn: 53937

as a questionable case, but the code isn't actually needed.

llvm-svn: 52657

Enhanced heuristic to determine the *best* register to spill. Instead of picking the register with the lowest spill weight. Consider (up to) 2 additional registers with spill weights that are close to the lowest spill weight. The one with fewest defs and uses that conflicts with the current interval (weighted by loop depth) is the spill candidate.

This is not always a win, but there are much more wins than loses and wins tend to be more noticeable.

llvm-svn: 52554

llvm-svn: 52040

llvm-svn: 51934