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Fix liveness computations in BranchFolding. 

The old code would look at kills and defs in one pass over the
instruction operands, causing problems with this code:

  %R0<def>, %CPSR<def,dead> = tLSLri %R5<kill>, 2, pred:14, pred:%noreg
  %R0<def>, %CPSR<def,dead> = tADDrr %R4<kill>, %R0<kill>, pred:14, %pred:%noreg

The last instruction kills and redefines %R0, so it is still live after
the instruction.

This caused a register scavenger crash when compiling 483.xalancbmk for
armv6. I am not including a test case because it requires too much bad
luck to expose this old bug.

First you need to convince the register allocator to use %R0 twice on
the tADDrr instruction, then you have to convince BranchFolding to do
something that causes it to run the register scavenger on he bad block.

<rdar://problem/9898200>

llvm-svn: 136973
This commit is contained in:
Jakob Stoklund Olesen 2011-08-05 18:47:07 +00:00
parent 30097b7c41
commit d633abebf6
1 changed files with 16 additions and 13 deletions
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29
llvm/lib/CodeGen/BranchFolding.cpp
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@ -1624,26 +1624,29 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
if (!TIB->isSafeToMove(TII, 0, DontMoveAcrossStore)) if (!TIB->isSafeToMove(TII, 0, DontMoveAcrossStore))
break; break;
// Remove kills from LocalDefsSet, these registers had short live ranges.
for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) {
MachineOperand &MO = TIB->getOperand(i);
if (!MO.isReg() || !MO.isUse() || !MO.isKill())
continue;
unsigned Reg = MO.getReg();
if (!Reg || !LocalDefsSet.count(Reg))
continue;
for (const unsigned *OR = TRI->getOverlaps(Reg); *OR; ++OR)
LocalDefsSet.erase(*OR);
}
// Track local defs so we can update liveins. // Track local defs so we can update liveins.
for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) { for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) {
MachineOperand &MO = TIB->getOperand(i); MachineOperand &MO = TIB->getOperand(i);
if (!MO.isReg()) if (!MO.isReg() || !MO.isDef() || MO.isDead())
continue; continue;
unsigned Reg = MO.getReg(); unsigned Reg = MO.getReg();
if (!Reg) if (!Reg)
continue; continue;
if (MO.isDef()) { LocalDefs.push_back(Reg);
if (!MO.isDead()) { for (const unsigned *OR = TRI->getOverlaps(Reg); *OR; ++OR)
LocalDefs.push_back(Reg); LocalDefsSet.insert(*OR);
LocalDefsSet.insert(Reg);
for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
LocalDefsSet.insert(*SR);
}
} else if (MO.isKill() && LocalDefsSet.count(Reg)) {
LocalDefsSet.erase(Reg);
for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
LocalDefsSet.erase(*SR);
}
} }
HasDups = true;; HasDups = true;;