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Simplify INSERT_SUBREG emission.

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The register class created by INSERT_SUBREG and SUBREG_TO_REG must be
legal and support the SubIdx sub-registers.

The new getSubClassWithSubReg() hook can compute that.

This may create INSERT_SUBREG instructions defining a larger register
class than the sub-register being inserted.  That is OK,
RegisterCoalescer will constrain the register class as needed when it
eliminates the INSERT_SUBREG instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141198 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2011-10-05 18:31:00 +00:00
parent 42be280a28
commit 2c3bef8a15
1 changed files with 19 additions and 27 deletions
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46
lib/CodeGen/SelectionDAG/InstrEmitter.cpp
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@ -392,21 +392,6 @@ void InstrEmitter::AddOperand(MachineInstr *MI, SDValue Op,
}
}
/// getSuperRegisterRegClass - Returns the register class of a superreg A whose
/// "SubIdx"'th sub-register class is the specified register class and whose
/// type matches the specified type.
static const TargetRegisterClass*
getSuperRegisterRegClass(const TargetRegisterClass *TRC,
unsigned SubIdx, EVT VT) {
// Pick the register class of the superegister for this type
for (TargetRegisterInfo::regclass_iterator I = TRC->superregclasses_begin(),
E = TRC->superregclasses_end(); I != E; ++I)
if ((*I)->hasType(VT) && (*I)->getSubRegisterRegClass(SubIdx) == TRC)
return *I;
assert(false && "Couldn't find the register class");
return 0;
}
/// EmitSubregNode - Generate machine code for subreg nodes.
///
void InstrEmitter::EmitSubregNode(SDNode *Node,
@ -482,21 +467,28 @@ void InstrEmitter::EmitSubregNode(SDNode *Node,
SDValue N0 = Node->getOperand(0);
SDValue N1 = Node->getOperand(1);
SDValue N2 = Node->getOperand(2);
unsigned SubReg = getVR(N1, VRBaseMap);
unsigned SubIdx = cast<ConstantSDNode>(N2)->getZExtValue();
const TargetRegisterClass *TRC = MRI->getRegClass(SubReg);
const TargetRegisterClass *SRC =
getSuperRegisterRegClass(TRC, SubIdx, Node->getValueType(0));
// Figure out the register class to create for the destreg.
// Note that if we're going to directly use an existing register,
// it must be precisely the required class, and not a subclass
// thereof.
if (VRBase == 0 || SRC != MRI->getRegClass(VRBase)) {
// Create the reg
assert(SRC && "Couldn't find source register class");
// Figure out the register class to create for the destreg. It should be
// the largest legal register class supporting SubIdx sub-registers.
// RegisterCoalescer will constrain it further if it decides to eliminate
// the INSERT_SUBREG instruction.
//
// %dst = INSERT_SUBREG %src, %sub, SubIdx
//
// is lowered by TwoAddressInstructionPass to:
//
// %dst = COPY %src
// %dst:SubIdx = COPY %sub
//
// There is no constraint on the %src register class.
//
const TargetRegisterClass *SRC = TLI->getRegClassFor(Node->getValueType(0));
SRC = TRI->getSubClassWithSubReg(SRC, SubIdx);
assert(SRC && "No register class supports VT and SubIdx for INSERT_SUBREG");
if (VRBase == 0 || !SRC->hasSubClassEq(MRI->getRegClass(VRBase)))
VRBase = MRI->createVirtualRegister(SRC);
}
// Create the insert_subreg or subreg_to_reg machine instruction.
MachineInstr *MI = BuildMI(*MF, Node->getDebugLoc(), TII->get(Opc));