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Add a last resort tryInstructionSplit() to RAGreedy.

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Live ranges with a constrained register class may benefit from splitting
around individual uses. It allows the remaining live range to use a
larger register class where it may allocate. This is like spilling to a
different register class.

This is only attempted on constrained register classes.

<rdar://problem/11438902>

llvm-svn: 157354
This commit is contained in:
Jakob Stoklund Olesen 2012-05-23 22:37:27 +00:00
parent ad5fae97e3
commit 2313afcd00
2 changed files with 87 additions and 1 deletions
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66
lib/CodeGen/RegAllocGreedy.cpp
View File

@ -286,6 +286,8 @@ private:
SmallVectorImpl<LiveInterval*>&);
unsigned tryBlockSplit(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
unsigned tryInstructionSplit(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
unsigned tryLocalSplit(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
unsigned trySplit(LiveInterval&, AllocationOrder&,
@ -1265,6 +1267,65 @@ unsigned RAGreedy::tryBlockSplit(LiveInterval &VirtReg, AllocationOrder &Order,
return 0;
}
//===----------------------------------------------------------------------===//
// Per-Instruction Splitting
//===----------------------------------------------------------------------===//
/// tryInstructionSplit - Split a live range around individual instructions.
/// This is normally not worthwhile since the spiller is doing essentially the
/// same thing. However, when the live range is in a constrained register
/// class, it may help to insert copies such that parts of the live range can
/// be moved to a larger register class.
///
/// This is similar to spilling to a larger register class.
unsigned
RAGreedy::tryInstructionSplit(LiveInterval &VirtReg, AllocationOrder &Order,
SmallVectorImpl<LiveInterval*> &NewVRegs) {
// There is no point to this if there are no larger sub-classes.
if (!RegClassInfo.isProperSubClass(MRI->getRegClass(VirtReg.reg)))
return 0;
// Always enable split spill mode, since we're effectively spilling to a
// register.
LiveRangeEdit LREdit(&VirtReg, NewVRegs, *MF, *LIS, VRM, this);
SE->reset(LREdit, SplitEditor::SM_Size);
ArrayRef<SlotIndex> Uses = SA->getUseSlots();
if (Uses.size() <= 1)
return 0;
DEBUG(dbgs() << "Split around " << Uses.size() << " individual instrs.\n");
// Split around every non-copy instruction.
for (unsigned i = 0; i != Uses.size(); ++i) {
if (const MachineInstr *MI = Indexes->getInstructionFromIndex(Uses[i]))
if (MI->isFullCopy()) {
DEBUG(dbgs() << " skip:\t" << Uses[i] << '\t' << *MI);
continue;
}
SE->openIntv();
SlotIndex SegStart = SE->enterIntvBefore(Uses[i]);
SlotIndex SegStop = SE->leaveIntvAfter(Uses[i]);
SE->useIntv(SegStart, SegStop);
}
if (LREdit.empty()) {
DEBUG(dbgs() << "All uses were copies.\n");
return 0;
}
SmallVector<unsigned, 8> IntvMap;
SE->finish(&IntvMap);
DebugVars->splitRegister(VirtReg.reg, LREdit.regs());
ExtraRegInfo.resize(MRI->getNumVirtRegs());
// Assign all new registers to RS_Spill. This was the last chance.
setStage(LREdit.begin(), LREdit.end(), RS_Spill);
return 0;
}
//===----------------------------------------------------------------------===//
// Local Splitting
//===----------------------------------------------------------------------===//
@ -1561,7 +1622,10 @@ unsigned RAGreedy::trySplit(LiveInterval &VirtReg, AllocationOrder &Order,
if (LIS->intervalIsInOneMBB(VirtReg)) {
NamedRegionTimer T("Local Splitting", TimerGroupName, TimePassesIsEnabled);
SA->analyze(&VirtReg);
return tryLocalSplit(VirtReg, Order, NewVRegs);
unsigned PhysReg = tryLocalSplit(VirtReg, Order, NewVRegs);
if (PhysReg || !NewVRegs.empty())
return PhysReg;
return tryInstructionSplit(VirtReg, Order, NewVRegs);
}
NamedRegionTimer T("Global Splitting", TimerGroupName, TimePassesIsEnabled);

22
test/CodeGen/Thumb2/inflate-regs.ll Normal file
View File

@ -0,0 +1,22 @@
; RUN: llc < %s -mcpu=cortex-a8 | FileCheck %s
target triple = "thumbv7-apple-ios"
; CHECK: local_split
;
; The load must go into d0-15 which are all clobbered by the asm.
; RAGreedy should split the range and use d16-d31 to avoid a spill.
;
; CHECK: vldr s
; CHECK-NOT: vstr
; CHECK: vadd.f32
; CHECK-NOT: vstr
; CHECK: vorr
; CHECK: vstr s
define void @local_split(float* nocapture %p) nounwind ssp {
entry:
%x = load float* %p, align 4
%a = fadd float %x, 1.0
tail call void asm sideeffect "", "~{d0},~{d1},~{d2},~{d3},~{d4},~{d5},~{d6},~{d7},~{d8},~{d9},~{d10},~{d11},~{d12},~{d13},~{d14},~{d15}"() nounwind
store float %a, float* %p, align 4
ret void
}