if ((impGetNonPrefixOpcode(codeAddr, codeEndp) == CEE_LDNULL))

switch (impGetNonPrefixOpcode(codeAddr + 1, codeEndp))

{

case CEE_CGT_UN:

// isinst + ldnull + cgt.un

// convert to op1 == null ? false : *op1 == op2

{

GenTree* condNull;

//

// expand the null check:

//

// condNull ==> GT_NE

// / \.

// op1Copy CNS_INT

// null

//

condNull = gtNewOperNode(GT_NE, TYP_INT, gtClone(op1), gtNewNull());

GenTree* temp;

GenTree* condMT;

//

// expand the methodtable match:

//

// condMT ==> GT_EQ

// / \.

// GT_IND op2 (typically CNS_INT)

// |

// op1Copy

//

// This can replace op1 with a GT_COMMA that evaluates op1 into a local

//

op1 = impCloneExpr(op1, &temp, CHECK_SPILL_ALL, nullptr DEBUGARG("CASTCLASS eval op1"));

//

// op1 is now known to be a non-complex tree

// thus we can use gtClone(op1) from now on

//

GenTree* op2Var = op2;

temp = gtNewMethodTableLookup(temp);

condMT = gtNewOperNode(GT_EQ, TYP_INT, temp, op2);

GenTree* qmarkNull;

//

// Generate QMARK - COLON tree

//

// qmarkNull ==> GT_QMARK

// / \.

// condNull GT_COLON

// / \.

// condMT CNS_INT

// false

//

temp = new (this, GT_COLON) GenTreeColon(TYP_INT, condMT, gtNewFalse());

qmarkNull = gtNewQmarkNode(TYP_INT, condNull, temp->AsColon());

// Make QMark node a top level node by spilling it.

unsigned tmp = lvaGrabTemp(true DEBUGARG("spilling QMark"));

impStoreTemp(tmp, qmarkNull, CHECK_SPILL_NONE);

GenTree* lclVar = gtNewLclvNode(tmp, TYP_INT);

impPushOnStack(lclVar, TYP_INT);

return 3;

}

case CEE_CEQ:

// isinst + ldnull + ceq

// convert to op1 == null ? true : *op1 != op2

break;

case CEE_BRTRUE:

case CEE_BRTRUE_S:

break;

case CEE_BRFALSE:

case CEE_BRFALSE_S:

break;

default:

return -1;

}