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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.

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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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70787 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2009-05-03 18:32:42 +00:00
parent 87e3caf819
commit c781a243a3
12 changed files with 477 additions and 173 deletions
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2
include/llvm/Target/TargetInstrInfo.h
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@@ -391,7 +391,7 @@ public:
/// possible, returns true as well as the new instructions by reference.
virtual bool unfoldMemoryOperand(MachineFunction &MF, MachineInstr *MI,
unsigned Reg, bool UnfoldLoad, bool UnfoldStore,
SmallVectorImpl<MachineInstr*> &NewMIs) const{
SmallVectorImpl<MachineInstr*> &NewMIs) const{
return false;
}

12
include/llvm/Target/TargetRegisterInfo.h
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@@ -238,8 +238,6 @@ public:
return end();
}
/// getSize - Return the size of the register in bytes, which is also the size
/// of a stack slot allocated to hold a spilled copy of this register.
unsigned getSize() const { return RegSize; }
@@ -254,10 +252,6 @@ public:
int getCopyCost() const { return CopyCost; }
};
/// getCommonSubClass - find the largest common subclass of A and B. Return NULL
/// if there is no common subclass.
const TargetRegisterClass *getCommonSubClass(const TargetRegisterClass *A,
const TargetRegisterClass *B);
/// TargetRegisterInfo base class - We assume that the target defines a static
/// array of TargetRegisterDesc objects that represent all of the machine
@@ -644,6 +638,7 @@ public:
virtual void getInitialFrameState(std::vector<MachineMove> &Moves) const;
};
// This is useful when building IndexedMaps keyed on virtual registers
struct VirtReg2IndexFunctor : std::unary_function<unsigned, unsigned> {
unsigned operator()(unsigned Reg) const {
@@ -651,6 +646,11 @@ struct VirtReg2IndexFunctor : std::unary_function<unsigned, unsigned> {
}
};
/// getCommonSubClass - find the largest common subclass of A and B. Return NULL
/// if there is no common subclass.
const TargetRegisterClass *getCommonSubClass(const TargetRegisterClass *A,
const TargetRegisterClass *B);
} // End llvm namespace
#endif