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Overview
Comment:Additional small performance increase and size reduction to the sqlite3VdbeMakeLabel() mechanism.
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SHA3-256: 1bdee199a71e0a6c247b85e72de9e3a3099b7179c33288735721facef3b96459
User & Date: drh 2018-12-29 14:23:22
Context
2018-12-31
16:36
Fix the OP_OpenEphemeral opcode in the bytecode engine so that if it is called a second or subsequent time, it merely clears the existing table rather than creating a new one. Proposed fix for ticket [d0866b26f83e9c55e30de0821f5d]. check-in: 4678cb10 user: drh tags: trunk
2018-12-29
14:23
Additional small performance increase and size reduction to the sqlite3VdbeMakeLabel() mechanism. check-in: 1bdee199 user: drh tags: trunk
02:26
A new implementation of sqlite3VdbeMakeLabel() is faster and makes fewer memory allocations by deferring memory allocation until sqlite3VdbeResolveLabel() is called, at which point the code generator has a better idea of how big the relocation table needs to be. The sqlite3VdbeMakeLabel() routine now takes a Parse* parameter instead of Vdbe*. check-in: 4a0929ac user: drh tags: trunk
Changes
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Changes to src/sqliteInt.h.

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  int iRangeReg;       /* First register in temporary register block */
  int nErr;            /* Number of errors seen */
  int nTab;            /* Number of previously allocated VDBE cursors */
  int nMem;            /* Number of memory cells used so far */
  int szOpAlloc;       /* Bytes of memory space allocated for Vdbe.aOp[] */
  int iSelfTab;        /* Table associated with an index on expr, or negative
                       ** of the base register during check-constraint eval */
  int nLabel;          /* Number of labels used */
  int nLabelAlloc;     /* Number of slots in aLabel */
  int *aLabel;         /* Space to hold the labels */
  ExprList *pConstExpr;/* Constant expressions */
  Token constraintName;/* Name of the constraint currently being parsed */
  yDbMask writeMask;   /* Start a write transaction on these databases */
  yDbMask cookieMask;  /* Bitmask of schema verified databases */
  int regRowid;        /* Register holding rowid of CREATE TABLE entry */







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  int iRangeReg;       /* First register in temporary register block */
  int nErr;            /* Number of errors seen */
  int nTab;            /* Number of previously allocated VDBE cursors */
  int nMem;            /* Number of memory cells used so far */
  int szOpAlloc;       /* Bytes of memory space allocated for Vdbe.aOp[] */
  int iSelfTab;        /* Table associated with an index on expr, or negative
                       ** of the base register during check-constraint eval */
  int nLabel;          /* The *negative* of the number of labels used */
  int nLabelAlloc;     /* Number of slots in aLabel */
  int *aLabel;         /* Space to hold the labels */
  ExprList *pConstExpr;/* Constant expressions */
  Token constraintName;/* Name of the constraint currently being parsed */
  yDbMask writeMask;   /* Start a write transaction on these databases */
  yDbMask cookieMask;  /* Bitmask of schema verified databases */
  int regRowid;        /* Register holding rowid of CREATE TABLE entry */

Changes to src/vdbe.h.

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#   define COLNAME_N      1      /* Store only the name */
# else
#   define COLNAME_N      2      /* Store the name and decltype */
# endif
#endif

/*
** The following macro converts a relative address in the p2 field
** of a VdbeOp structure into a negative number so that 
** sqlite3VdbeAddOpList() knows that the address is relative.  Calling
** the macro again restores the address.
*/
#define ADDR(X)  (-1-(X))

/*
** The makefile scans the vdbe.c source file and creates the "opcodes.h"
** header file that defines a number for each opcode used by the VDBE.
*/
#include "opcodes.h"








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#   define COLNAME_N      1      /* Store only the name */
# else
#   define COLNAME_N      2      /* Store the name and decltype */
# endif
#endif

/*
** The following macro converts a label returned by sqlite3VdbeMakeLabel()
** into an index into the Parse.aLabel[] array that contains the resolved
** address of that label.

*/
#define ADDR(X)  (~(X))

/*
** The makefile scans the vdbe.c source file and creates the "opcodes.h"
** header file that defines a number for each opcode used by the VDBE.
*/
#include "opcodes.h"

Changes to src/vdbeaux.c.

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** the label is resolved to a specific address, the VDBE will scan
** through its operation list and change all values of P2 which match
** the label into the resolved address.
**
** The VDBE knows that a P2 value is a label because labels are
** always negative and P2 values are suppose to be non-negative.
** Hence, a negative P2 value is a label that has yet to be resolved.


**
** Zero is returned if a malloc() fails.










*/
int sqlite3VdbeMakeLabel(Parse *pParse){
  return ADDR(pParse->nLabel++);
}

/*
** Resolve label "x" to be the address of the next instruction to
** be inserted.  The parameter "x" must have been obtained from
** a prior call to sqlite3VdbeMakeLabel().
*/
static SQLITE_NOINLINE void resizeResolveLabel(Parse *p, Vdbe *v, int j){
  int nNewSize = p->nLabel+10;
  p->aLabel = sqlite3DbReallocOrFree(p->db, p->aLabel,
                     nNewSize*sizeof(p->aLabel[0]));
  if( p->aLabel==0 ){
    p->nLabelAlloc = 0;
  }else{
#ifdef SQLITE_DEBUG
    int i;
................................................................................
    p->aLabel[j] = v->nOp;
  }
}
void sqlite3VdbeResolveLabel(Vdbe *v, int x){
  Parse *p = v->pParse;
  int j = ADDR(x);
  assert( v->magic==VDBE_MAGIC_INIT );
  assert( j<p->nLabel );
  assert( j>=0 );
#ifdef SQLITE_DEBUG
  if( p->db->flags & SQLITE_VdbeAddopTrace ){
    printf("RESOLVE LABEL %d to %d\n", x, v->nOp);
  }
#endif
  if( p->nLabelAlloc < p->nLabel ){
    resizeResolveLabel(p,v,j);
  }else{
    assert( p->aLabel[j]==(-1) ); /* Labels may only be resolved once */
    p->aLabel[j] = v->nOp;
  }
}

................................................................................
#endif
        default: {
          if( pOp->p2<0 ){
            /* The mkopcodeh.tcl script has so arranged things that the only
            ** non-jump opcodes less than SQLITE_MX_JUMP_CODE are guaranteed to
            ** have non-negative values for P2. */
            assert( (sqlite3OpcodeProperty[pOp->opcode] & OPFLG_JUMP)!=0 );
            assert( ADDR(pOp->p2)<pParse->nLabel );
            pOp->p2 = aLabel[ADDR(pOp->p2)];
          }
          break;
        }
      }
      /* The mkopcodeh.tcl script has so arranged things that the only
      ** non-jump opcodes less than SQLITE_MX_JUMP_CODE are guaranteed to







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** the label is resolved to a specific address, the VDBE will scan
** through its operation list and change all values of P2 which match
** the label into the resolved address.
**
** The VDBE knows that a P2 value is a label because labels are
** always negative and P2 values are suppose to be non-negative.
** Hence, a negative P2 value is a label that has yet to be resolved.
** (Later:) This is only true for opcodes that have the OPFLG_JUMP
** property.
**

** Variable usage notes:
**
**     Parse.aLabel[x]     Stores the address that the x-th label resolves
**                         into.  For testing (SQLITE_DEBUG), unresolved
**                         labels stores -1, but that is not required.
**     Parse.nLabelAlloc   Number of slots allocated to Parse.aLabel[]
**     Parse.nLabel        The *negative* of the number of labels that have
**                         been issued.  The negative is stored because
**                         that gives a performance improvement over storing
**                         the equivalent positive value.
*/
int sqlite3VdbeMakeLabel(Parse *pParse){
  return --pParse->nLabel;
}

/*
** Resolve label "x" to be the address of the next instruction to
** be inserted.  The parameter "x" must have been obtained from
** a prior call to sqlite3VdbeMakeLabel().
*/
static SQLITE_NOINLINE void resizeResolveLabel(Parse *p, Vdbe *v, int j){
  int nNewSize = 10 - p->nLabel;
  p->aLabel = sqlite3DbReallocOrFree(p->db, p->aLabel,
                     nNewSize*sizeof(p->aLabel[0]));
  if( p->aLabel==0 ){
    p->nLabelAlloc = 0;
  }else{
#ifdef SQLITE_DEBUG
    int i;
................................................................................
    p->aLabel[j] = v->nOp;
  }
}
void sqlite3VdbeResolveLabel(Vdbe *v, int x){
  Parse *p = v->pParse;
  int j = ADDR(x);
  assert( v->magic==VDBE_MAGIC_INIT );
  assert( j<-p->nLabel );
  assert( j>=0 );
#ifdef SQLITE_DEBUG
  if( p->db->flags & SQLITE_VdbeAddopTrace ){
    printf("RESOLVE LABEL %d to %d\n", x, v->nOp);
  }
#endif
  if( p->nLabelAlloc + p->nLabel < 0 ){
    resizeResolveLabel(p,v,j);
  }else{
    assert( p->aLabel[j]==(-1) ); /* Labels may only be resolved once */
    p->aLabel[j] = v->nOp;
  }
}

................................................................................
#endif
        default: {
          if( pOp->p2<0 ){
            /* The mkopcodeh.tcl script has so arranged things that the only
            ** non-jump opcodes less than SQLITE_MX_JUMP_CODE are guaranteed to
            ** have non-negative values for P2. */
            assert( (sqlite3OpcodeProperty[pOp->opcode] & OPFLG_JUMP)!=0 );
            assert( ADDR(pOp->p2)<-pParse->nLabel );
            pOp->p2 = aLabel[ADDR(pOp->p2)];
          }
          break;
        }
      }
      /* The mkopcodeh.tcl script has so arranged things that the only
      ** non-jump opcodes less than SQLITE_MX_JUMP_CODE are guaranteed to