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Make local RA smarter about reusing input register of a copy

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as output.  Needed for (functional) correctness in inline asm,
and should be generally beneficial.  7361612.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95050 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dale Johannesen
2010-02-02 02:08:02 +00:00
parent 44eedb9805
commit 5ce0ee9c09
3 changed files with 18 additions and 2 deletions
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14
lib/CodeGen/RegAllocLocal.cpp
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@@ -764,8 +764,11 @@ void RALocal::AllocateBasicBlock(MachineBasicBlock &MBB) {
// Determine whether this is a copy instruction. The cases where the
// source or destination are phys regs are handled specially.
unsigned SrcCopyReg, DstCopyReg, SrcCopySubReg, DstCopySubReg;
unsigned SrcCopyPhysReg = 0U;
bool isCopy = TII->isMoveInstr(*MI, SrcCopyReg, DstCopyReg,
SrcCopySubReg, DstCopySubReg);
if (isCopy && TargetRegisterInfo::isVirtualRegister(SrcCopyReg))
SrcCopyPhysReg = getVirt2PhysRegMapSlot(SrcCopyReg);
// Loop over the implicit uses, making sure that they are at the head of the
// use order list, so they don't get reallocated.
@@ -977,13 +980,24 @@ void RALocal::AllocateBasicBlock(MachineBasicBlock &MBB) {
// If DestVirtReg already has a value, use it.
if (!(DestPhysReg = getVirt2PhysRegMapSlot(DestVirtReg))) {
// If this is a copy try to reuse the input as the output;
// that will make the copy go away.
// If this is a copy, the source reg is a phys reg, and
// that reg is available, use that phys reg for DestPhysReg.
// If this is a copy, the source reg is a virtual reg, and
// the phys reg that was assigned to that virtual reg is now
// available, use that phys reg for DestPhysReg. (If it's now
// available that means this was the last use of the source.)
if (isCopy &&
TargetRegisterInfo::isPhysicalRegister(SrcCopyReg) &&
isPhysRegAvailable(SrcCopyReg)) {
DestPhysReg = SrcCopyReg;
assignVirtToPhysReg(DestVirtReg, DestPhysReg);
} else if (isCopy &&
TargetRegisterInfo::isVirtualRegister(SrcCopyReg) &&
SrcCopyPhysReg && isPhysRegAvailable(SrcCopyPhysReg)) {
DestPhysReg = SrcCopyPhysReg;
assignVirtToPhysReg(DestVirtReg, DestPhysReg);
} else
DestPhysReg = getReg(MBB, MI, DestVirtReg);
}