SQLite

  for(i=0; i<pTab->nCol; i++){
    if( i==pTab->iPKey ){
      sqlite3VdbeAddOp2(v, OP_Null, 0, regNew+i);
    }else{
      j = aXRef[i];
      if( j>=0 ){
        sqlite3ExprCode(pParse, pChanges->a[j].pExpr, regNew+i);
        if( tmask&TRIGGER_BEFORE ){
          /* Must preserve copied values even in case the original is
          ** reloaded in the After-BEFORE-trigger-reload-loop below.
          ** Ticket d85fffd6ffe856092ed8daefa811b1e399706b28 */
          sqlite3VdbeSwapOpcode(v, -1, OP_SCopy, OP_Copy);
        }
      }else if( 0==(tmask&TRIGGER_BEFORE) || i>31 || (newmask & MASKBIT32(i)) ){
        /* This branch loads the value of a column that will not be changed 
        ** into a register. This is done if there are no BEFORE triggers, or
        ** if there are one or more BEFORE triggers that use this value via
        ** a new.* reference in a trigger program.
        */
        testcase( i==31 );

      sqlite3VdbeAddOp4Int(v, OP_NotFound, iDataCur, labelContinue,regKey,nKey);
      VdbeCoverage(v);
    }else{
      sqlite3VdbeAddOp3(v, OP_NotExists, iDataCur, labelContinue, regOldRowid);
      VdbeCoverage(v);
    }

    /* After-BEFORE-trigger-reload-loop:
    ** If it did not delete it, the BEFORE trigger may still have modified 
    ** some of the columns of the row being updated. Load the values for 
    ** all columns not modified by the update statement into their registers
    ** in case this has happened. Only unmodified columns are reloaded.
    ** The values computed for modified columns use the values before the
    ** BEFORE trigger runs.  See test case trigger1-18.0 (added 2018-04-26)
    ** for an example.
    */

#else
# define sqlite3VdbeVerifyNoMallocRequired(A,B)
# define sqlite3VdbeVerifyNoResultRow(A)
#endif
VdbeOp *sqlite3VdbeAddOpList(Vdbe*, int nOp, VdbeOpList const *aOp, int iLineno);
void sqlite3VdbeAddParseSchemaOp(Vdbe*,int,char*);
void sqlite3VdbeChangeOpcode(Vdbe*, u32 addr, u8);
void sqlite3VdbeSwapOpcode(Vdbe*, u32 addr, u8, u8);
void sqlite3VdbeChangeP1(Vdbe*, u32 addr, int P1);
void sqlite3VdbeChangeP2(Vdbe*, u32 addr, int P2);
void sqlite3VdbeChangeP3(Vdbe*, u32 addr, int P3);
void sqlite3VdbeChangeP5(Vdbe*, u16 P5);
void sqlite3VdbeJumpHere(Vdbe*, int addr);
int sqlite3VdbeChangeToNoop(Vdbe*, int addr);
int sqlite3VdbeDeletePriorOpcode(Vdbe*, u8 op);

void sqlite3VdbeChangeP3(Vdbe *p, u32 addr, int val){
  sqlite3VdbeGetOp(p,addr)->p3 = val;
}
void sqlite3VdbeChangeP5(Vdbe *p, u16 p5){
  assert( p->nOp>0 || p->db->mallocFailed );
  if( p->nOp>0 ) p->aOp[p->nOp-1].p5 = p5;
}

/* Change the opcode to iNew if it was previously iOld */
void sqlite3VdbeSwapOpcode(Vdbe *p, u32 addr, u8 iOld, u8 iNew){
  VdbeOp *pOp = sqlite3VdbeGetOp(p,addr);
  if( pOp->opcode==iOld ) pOp->opcode = iNew;
}

/*
** Change the P2 operand of instruction addr so that it points to
** the address of the next instruction to be coded.
*/
void sqlite3VdbeJumpHere(Vdbe *p, int addr){
  sqlite3VdbeChangeP2(p, addr, p->nOp);

} {1 1000 2}  ;# Not: 1 1000 1000 
do_execsql_test trigger1-18.1 {
  DELETE FROM t18;
  INSERT INTO t18(a,b,c) VALUES(1,2,3);
  UPDATE t18 SET c=b, b=b+1 WHERE a=1;
  SELECT * FROM t18;
} {1 3 2}     ;# Not: 1 1001 1000

# 2018-04-26 ticket [https://www.sqlite.org/src/tktview/d85fffd6ffe856092e]
# VDBE Program uses an expired value.
#
do_execsql_test trigger1-19.0 {
  CREATE TABLE t19(a INT PRIMARY KEY, b, c)WITHOUT ROWID;
  INSERT INTO t19(a,b,c) VALUES(1,2,3);
  CREATE TRIGGER t19r3 BEFORE UPDATE ON t19 BEGIN SELECT new.b; END;
  UPDATE t19 SET c=b WHERE a=1;
  SELECT * FROM t19;
} {1 2 2}

finish_test