Additional small performance increase and size reduction to the

sqlite3VdbeMakeLabel() mechanism.

FossilOrigin-Name: 1bdee199a71e0a6c247b85e72de9e3a3099b7179c33288735721facef3b96459

3 files changed, 22 insertions, 12 deletions

diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 1db0bc4c8..e056088fc 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -3068,7 +3068,7 @@ struct Parse {
   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 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 */
diff --git a/src/vdbe.h b/src/vdbe.h
index 7a0312a04..8928798f1 100644
--- a/src/vdbe.h
+++ b/src/vdbe.h
@@ -156,12 +156,11 @@ typedef struct VdbeOpList VdbeOpList;
 #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.
+** 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)  (-1-(X))
+#define ADDR(X)  (~(X))
 
 /*
 ** The makefile scans the vdbe.c source file and creates the "opcodes.h"
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index 77e72e046..193b24db8 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -445,11 +445,22 @@ void sqlite3VdbeEndCoroutine(Vdbe *v, int regYield){
 ** 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.
 **
-** Zero is returned if a malloc() fails.
+** 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 ADDR(pParse->nLabel++);
+  return --pParse->nLabel;
 }
 
 /*
@@ -458,7 +469,7 @@ int sqlite3VdbeMakeLabel(Parse *pParse){
 ** a prior call to sqlite3VdbeMakeLabel().
 */
 static SQLITE_NOINLINE void resizeResolveLabel(Parse *p, Vdbe *v, int j){
-  int nNewSize = p->nLabel+10;
+  int nNewSize = 10 - p->nLabel;
   p->aLabel = sqlite3DbReallocOrFree(p->db, p->aLabel,
                      nNewSize*sizeof(p->aLabel[0]));
   if( p->aLabel==0 ){
@@ -476,14 +487,14 @@ 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<-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 ){
+  if( p->nLabelAlloc + p->nLabel < 0 ){
     resizeResolveLabel(p,v,j);
   }else{
     assert( p->aLabel[j]==(-1) ); /* Labels may only be resolved once */
@@ -761,7 +772,7 @@ static void resolveP2Values(Vdbe *p, int *pMaxFuncArgs){
             ** 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 );
+            assert( ADDR(pOp->p2)<-pParse->nLabel );
             pOp->p2 = aLabel[ADDR(pOp->p2)];
           }
           break;