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Fix evil VirtRegRewriter bug. 

The rewriter can keep track of multiple stack slots in the same register if they
happen to have the same value. When an instruction modifies a stack slot by
defining a register that is mapped to a stack slot, other stack slots in that
register are no longer valid.

This is a very rare problem, and I don't have a simple test case. I get the
impression that VirtRegRewriter knows it is about to be deleted, inventing a
last opaque problem.

<rdar://problem/9204040>

llvm-svn: 128562
This commit is contained in:
Jakob Stoklund Olesen 2011-03-30 18:14:07 +00:00
parent 69129256dd
commit ae917a3740
1 changed files with 28 additions and 0 deletions
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28
llvm/lib/CodeGen/VirtRegRewriter.cpp
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@ -261,6 +261,10 @@ public:
/// now).
void ModifyStackSlotOrReMat(int SlotOrReMat);
/// ClobberSharingStackSlots - When a register mapped to a stack slot changes,
/// other stack slots sharing the same register are no longer valid.
void ClobberSharingStackSlots(int StackSlot);
/// AddAvailableRegsToLiveIn - Availability information is being kept coming
/// into the specified MBB. Add available physical registers as potential
/// live-in's. If they are reused in the MBB, they will be added to the
@ -831,6 +835,26 @@ void AvailableSpills::ModifyStackSlotOrReMat(int SlotOrReMat) {
PhysRegsAvailable.erase(I);
}
void AvailableSpills::ClobberSharingStackSlots(int StackSlot) {
std::map<int, unsigned>::iterator It =
SpillSlotsOrReMatsAvailable.find(StackSlot);
if (It == SpillSlotsOrReMatsAvailable.end()) return;
unsigned Reg = It->second >> 1;
// Erase entries in PhysRegsAvailable for other stack slots.
std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
while (I != PhysRegsAvailable.end() && I->first == Reg) {
std::multimap<unsigned, int>::iterator NextI = llvm::next(I);
if (I->second != StackSlot) {
DEBUG(dbgs() << "Clobbered sharing SS#" << I->second << " in "
<< PrintReg(Reg, TRI) << '\n');
SpillSlotsOrReMatsAvailable.erase(I->second);
PhysRegsAvailable.erase(I);
}
I = NextI;
}
}
// ************************** //
// Reuse Info Implementation //
// ************************** //
@ -2550,6 +2574,10 @@ LocalRewriter::RewriteMBB(LiveIntervals *LIs,
}
}
// If StackSlot is available in a register that also holds other stack
// slots, clobber those stack slots now.
Spills.ClobberSharingStackSlots(StackSlot);
assert(PhysReg && "VR not assigned a physical register?");
MRI->setPhysRegUsed(PhysReg);
unsigned RReg = SubIdx ? TRI->getSubReg(PhysReg, SubIdx) : PhysReg;