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Constrain register classes instead of emitting copies.

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Sometimes register class constraints are trivial, like GR32->GR32_NOSP,
or GPR->rGPR.  Teach InstrEmitter to simply constrain the virtual
register instead of emitting a copy in these cases.

Normally, these copies are handled by the coalescer.  This saves some
coalescer work.

llvm-svn: 140340
This commit is contained in:
Jakob Stoklund Olesen 2011-09-22 21:39:34 +00:00
parent 1d3105c3d3
commit dedb558e4d
1 changed files with 5 additions and 3 deletions
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8
lib/CodeGen/SelectionDAG/InstrEmitter.cpp
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@ -280,15 +280,17 @@ InstrEmitter::AddRegisterOperand(MachineInstr *MI, SDValue Op,
MCID.OpInfo[IIOpNum].isOptionalDef();
// If the instruction requires a register in a different class, create
// a new virtual register and copy the value into it.
// a new virtual register and copy the value into it, but first attempt to
// shrink VReg's register class within reason. For example, if VReg == GR32
// and II requires a GR32_NOSP, just constrain VReg to GR32_NOSP.
const unsigned MinRCSize = 4;
if (II) {
const TargetRegisterClass *SrcRC = MRI->getRegClass(VReg);
const TargetRegisterClass *DstRC = 0;
if (IIOpNum < II->getNumOperands())
DstRC = TII->getRegClass(*II, IIOpNum, TRI);
assert((DstRC || (MCID.isVariadic() && IIOpNum >= MCID.getNumOperands())) &&
"Don't have operand info for this instruction!");
if (DstRC && !SrcRC->hasSuperClassEq(DstRC)) {
if (DstRC && !MRI->constrainRegClass(VReg, DstRC, MinRCSize)) {
unsigned NewVReg = MRI->createVirtualRegister(DstRC);
BuildMI(*MBB, InsertPos, Op.getNode()->getDebugLoc(),
TII->get(TargetOpcode::COPY), NewVReg).addReg(VReg);