Merge micro-optimizations into trunk after fixing the build on MSVC.

Performance now shows 7.58% faster than the 3.8.6 release on x64 with
gcc 4.8.1 and -Os.

FossilOrigin-Name: 1de558bcb13edc4e9a42a0b05e4b0ed6b14286a4

13 files changed, 190 insertions, 181 deletions

diff --git a/src/btree.c b/src/btree.c
index fe34b4a83..522e945ac 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -4746,14 +4746,14 @@ int sqlite3BtreeMovetoUnpacked(
           ** single byte varint and the record fits entirely on the main
           ** b-tree page.  */
           testcase( pCell+nCell+1==pPage->aDataEnd );
-          c = xRecordCompare(nCell, (void*)&pCell[1], pIdxKey, 0);
+          c = xRecordCompare(nCell, (void*)&pCell[1], pIdxKey);
         }else if( !(pCell[1] & 0x80) 
           && (nCell = ((nCell&0x7f)<<7) + pCell[1])<=pPage->maxLocal
         ){
           /* The record-size field is a 2 byte varint and the record 
           ** fits entirely on the main b-tree page.  */
           testcase( pCell+nCell+2==pPage->aDataEnd );
-          c = xRecordCompare(nCell, (void*)&pCell[2], pIdxKey, 0);
+          c = xRecordCompare(nCell, (void*)&pCell[2], pIdxKey);
         }else{
           /* The record flows over onto one or more overflow pages. In
           ** this case the whole cell needs to be parsed, a buffer allocated
@@ -4774,7 +4774,7 @@ int sqlite3BtreeMovetoUnpacked(
             sqlite3_free(pCellKey);
             goto moveto_finish;
           }
-          c = xRecordCompare(nCell, pCellKey, pIdxKey, 0);
+          c = xRecordCompare(nCell, pCellKey, pIdxKey);
           sqlite3_free(pCellKey);
         }
         assert( 
diff --git a/src/func.c b/src/func.c
index 0a8a9dda3..e1961118f 100644
--- a/src/func.c
+++ b/src/func.c
@@ -1492,6 +1492,7 @@ static void minmaxStep(
       sqlite3SkipAccumulatorLoad(context);
     }
   }else{
+    pBest->db = sqlite3_context_db_handle(context);
     sqlite3VdbeMemCopy(pBest, pArg);
   }
 }
diff --git a/src/malloc.c b/src/malloc.c
index daf646bc3..a4acd2f0c 100644
--- a/src/malloc.c
+++ b/src/malloc.c
@@ -305,7 +305,7 @@ void *sqlite3Malloc(u64 n){
     p = 0;
   }else if( sqlite3GlobalConfig.bMemstat ){
     sqlite3_mutex_enter(mem0.mutex);
-    mallocWithAlarm(n, &p);
+    mallocWithAlarm((int)n, &p);
     sqlite3_mutex_leave(mem0.mutex);
   }else{
     p = sqlite3GlobalConfig.m.xMalloc((int)n);
@@ -549,7 +549,7 @@ void *sqlite3Realloc(void *pOld, u64 nBytes){
     pNew = pOld;
   }else if( sqlite3GlobalConfig.bMemstat ){
     sqlite3_mutex_enter(mem0.mutex);
-    sqlite3StatusSet(SQLITE_STATUS_MALLOC_SIZE, nBytes);
+    sqlite3StatusSet(SQLITE_STATUS_MALLOC_SIZE, (int)nBytes);
     nDiff = nNew - nOld;
     if( sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED) >= 
           mem0.alarmThreshold-nDiff ){
@@ -559,7 +559,7 @@ void *sqlite3Realloc(void *pOld, u64 nBytes){
     assert( sqlite3MemdebugNoType(pOld, ~MEMTYPE_HEAP) );
     pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
     if( pNew==0 && mem0.alarmCallback ){
-      sqlite3MallocAlarm(nBytes);
+      sqlite3MallocAlarm((int)nBytes);
       pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
     }
     if( pNew ){
@@ -699,7 +699,7 @@ void *sqlite3DbRealloc(sqlite3 *db, void *p, u64 n){
       assert( sqlite3MemdebugHasType(p, MEMTYPE_DB) );
       assert( sqlite3MemdebugHasType(p, MEMTYPE_LOOKASIDE|MEMTYPE_HEAP) );
       sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
-      pNew = sqlite3_realloc(p, n);
+      pNew = sqlite3_realloc64(p, n);
       if( !pNew ){
         sqlite3MemdebugSetType(p, MEMTYPE_DB|MEMTYPE_HEAP);
         db->mallocFailed = 1;
diff --git a/src/table.c b/src/table.c
index 12d0cf548..c435b2bc0 100644
--- a/src/table.c
+++ b/src/table.c
@@ -73,7 +73,7 @@ static int sqlite3_get_table_cb(void *pArg, int nCol, char **argv, char **colv){
       if( z==0 ) goto malloc_failed;
       p->azResult[p->nData++] = z;
     }
-  }else if( p->nColumn!=nCol ){
+  }else if( (int)p->nColumn!=nCol ){
     sqlite3_free(p->zErrMsg);
     p->zErrMsg = sqlite3_mprintf(
        "sqlite3_get_table() called with two or more incompatible queries"
diff --git a/src/utf.c b/src/utf.c
index 557f3a95e..549983f6f 100644
--- a/src/utf.c
+++ b/src/utf.c
@@ -314,10 +314,10 @@ SQLITE_NOINLINE int sqlite3VdbeMemTranslate(Mem *pMem, u8 desiredEnc){
   *z = 0;
   assert( (pMem->n+(desiredEnc==SQLITE_UTF8?1:2))<=len );
 
+  c = pMem->flags;
   sqlite3VdbeMemRelease(pMem);
-  pMem->flags &= ~(MEM_Static|MEM_Dyn|MEM_Ephem);
+  pMem->flags = MEM_Str|MEM_Term|(c&MEM_AffMask);
   pMem->enc = desiredEnc;
-  pMem->flags |= (MEM_Term);
   pMem->z = (char*)zOut;
   pMem->zMalloc = pMem->z;
 
diff --git a/src/vdbe.c b/src/vdbe.c
index cc9e317e4..f964a7387 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -640,7 +640,7 @@ int sqlite3VdbeExec(
       assert( pOp->p2<=(p->nMem-p->nCursor) );
       pOut = &aMem[pOp->p2];
       memAboutToChange(p, pOut);
-      VdbeMemReleaseExtern(pOut);
+      if( VdbeMemDynamic(pOut) ) sqlite3VdbeMemSetNull(pOut);
       pOut->flags = MEM_Int;
     }
 
@@ -1079,7 +1079,7 @@ case OP_Null: {           /* out2-prerelease */
   while( cnt>0 ){
     pOut++;
     memAboutToChange(p, pOut);
-    VdbeMemReleaseExtern(pOut);
+    sqlite3VdbeMemSetNull(pOut);
     pOut->flags = nullFlag;
     cnt--;
   }
@@ -1174,7 +1174,6 @@ case OP_Move: {
     }
 #endif
     pIn1->flags = MEM_Undefined;
-    pIn1->xDel = 0;
     pIn1->zMalloc = zMalloc;
     REGISTER_TRACE(p2++, pOut);
     pIn1++;
@@ -1912,8 +1911,14 @@ case OP_Ge: {             /* same as TK_GE, jump, in1, in3 */
     }
 
     assert( pOp->p4type==P4_COLLSEQ || pOp->p4.pColl==0 );
-    ExpandBlob(pIn1);
-    ExpandBlob(pIn3);
+    if( pIn1->flags & MEM_Zero ){
+      sqlite3VdbeMemExpandBlob(pIn1);
+      flags1 &= ~MEM_Zero;
+    }
+    if( pIn3->flags & MEM_Zero ){
+      sqlite3VdbeMemExpandBlob(pIn3);
+      flags3 &= ~MEM_Zero;
+    }
     res = sqlite3MemCompare(pIn3, pIn1, pOp->p4.pColl);
   }
   switch( pOp->opcode ){
@@ -1938,8 +1943,8 @@ case OP_Ge: {             /* same as TK_GE, jump, in1, in3 */
     }
   }
   /* Undo any changes made by applyAffinity() to the input registers. */
-  pIn1->flags = (pIn1->flags&~MEM_TypeMask) | (flags1&MEM_TypeMask);
-  pIn3->flags = (pIn3->flags&~MEM_TypeMask) | (flags3&MEM_TypeMask);
+  pIn1->flags = flags1;
+  pIn3->flags = flags3;
   break;
 }
 
@@ -2107,10 +2112,10 @@ case OP_Or: {             /* same as TK_OR, in1, in2, out3 */
 case OP_Not: {                /* same as TK_NOT, in1, out2 */
   pIn1 = &aMem[pOp->p1];
   pOut = &aMem[pOp->p2];
-  if( pIn1->flags & MEM_Null ){
-    sqlite3VdbeMemSetNull(pOut);
-  }else{
-    sqlite3VdbeMemSetInt64(pOut, !sqlite3VdbeIntValue(pIn1));
+  sqlite3VdbeMemSetNull(pOut);
+  if( (pIn1->flags & MEM_Null)==0 ){
+    pOut->flags = MEM_Int;
+    pOut->u.i = !sqlite3VdbeIntValue(pIn1);
   }
   break;
 }
@@ -2125,10 +2130,10 @@ case OP_Not: {                /* same as TK_NOT, in1, out2 */
 case OP_BitNot: {             /* same as TK_BITNOT, in1, out2 */
   pIn1 = &aMem[pOp->p1];
   pOut = &aMem[pOp->p2];
-  if( pIn1->flags & MEM_Null ){
-    sqlite3VdbeMemSetNull(pOut);
-  }else{
-    sqlite3VdbeMemSetInt64(pOut, ~sqlite3VdbeIntValue(pIn1));
+  sqlite3VdbeMemSetNull(pOut);
+  if( (pIn1->flags & MEM_Null)==0 ){
+    pOut->flags = MEM_Int;
+    pOut->u.i = ~sqlite3VdbeIntValue(pIn1);
   }
   break;
 }
@@ -2437,10 +2442,10 @@ case OP_Column: {
   assert( p2<pC->nHdrParsed );
   assert( rc==SQLITE_OK );
   assert( sqlite3VdbeCheckMemInvariants(pDest) );
+  if( VdbeMemDynamic(pDest) ) sqlite3VdbeMemSetNull(pDest);
   if( pC->szRow>=aOffset[p2+1] ){
     /* This is the common case where the desired content fits on the original
     ** page - where the content is not on an overflow page */
-    VdbeMemReleaseExtern(pDest);
     sqlite3VdbeSerialGet(pC->aRow+aOffset[p2], aType[p2], pDest);
   }else{
     /* This branch happens only when content is on overflow pages */
@@ -2449,37 +2454,23 @@ case OP_Column: {
           && ((t>=12 && (t&1)==0) || (pOp->p5 & OPFLAG_TYPEOFARG)!=0))
      || (len = sqlite3VdbeSerialTypeLen(t))==0
     ){
-      /* Content is irrelevant for the typeof() function and for
-      ** the length(X) function if X is a blob.  So we might as well use
-      ** bogus content rather than reading content from disk.  NULL works
-      ** for text and blob and whatever is in the payloadSize64 variable
-      ** will work for everything else.  Content is also irrelevant if
-      ** the content length is 0. */
-      zData = t<=13 ? (u8*)&payloadSize64 : 0;
-      sMem.zMalloc = 0;
+      /* Content is irrelevant for
+      **    1. the typeof() function,
+      **    2. the length(X) function if X is a blob, and
+      **    3. if the content length is zero.
+      ** So we might as well use bogus content rather than reading
+      ** content from disk.  NULL will work for the value for strings
+      ** and blobs and whatever is in the payloadSize64 variable
+      ** will work for everything else. */
+      sqlite3VdbeSerialGet(t<=13 ? (u8*)&payloadSize64 : 0, t, pDest);
     }else{
-      memset(&sMem, 0, sizeof(sMem));
-      sqlite3VdbeMemMove(&sMem, pDest);
       rc = sqlite3VdbeMemFromBtree(pCrsr, aOffset[p2], len, !pC->isTable,
-                                   &sMem);
+                                   pDest);
       if( rc!=SQLITE_OK ){
         goto op_column_error;
       }
-      zData = (u8*)sMem.z;
-    }
-    sqlite3VdbeSerialGet(zData, t, pDest);
-    /* If we dynamically allocated space to hold the data (in the
-    ** sqlite3VdbeMemFromBtree() call above) then transfer control of that
-    ** dynamically allocated space over to the pDest structure.
-    ** This prevents a memory copy. */
-    if( sMem.zMalloc ){
-      assert( sMem.z==sMem.zMalloc );
-      assert( VdbeMemDynamic(pDest)==0 );
-      assert( (pDest->flags & (MEM_Blob|MEM_Str))==0 || pDest->z==sMem.z );
-      pDest->flags &= ~(MEM_Ephem|MEM_Static);
-      pDest->flags |= MEM_Term;
-      pDest->z = sMem.z;
-      pDest->zMalloc = sMem.zMalloc;
+      sqlite3VdbeSerialGet((const u8*)pDest->z, t, pDest);
+      pDest->flags &= ~MEM_Ephem;
     }
   }
   pDest->enc = encoding;
@@ -2659,7 +2650,6 @@ case OP_MakeRecord: {
   assert( pOp->p3>0 && pOp->p3<=(p->nMem-p->nCursor) );
   pOut->n = (int)nByte;
   pOut->flags = MEM_Blob;
-  pOut->xDel = 0;
   if( nZero ){
     pOut->u.nZero = nZero;
     pOut->flags |= MEM_Zero;
@@ -4853,7 +4843,7 @@ case OP_IdxGE:  {       /* jump */
   { int i; for(i=0; i<r.nField; i++) assert( memIsValid(&r.aMem[i]) ); }
 #endif
   res = 0;  /* Not needed.  Only used to silence a warning. */
-  rc = sqlite3VdbeIdxKeyCompare(pC, &r, &res);
+  rc = sqlite3VdbeIdxKeyCompare(db, pC, &r, &res);
   assert( (OP_IdxLE&1)==(OP_IdxLT&1) && (OP_IdxGE&1)==(OP_IdxGT&1) );
   if( (pOp->opcode&1)==(OP_IdxLT&1) ){
     assert( pOp->opcode==OP_IdxLE || pOp->opcode==OP_IdxLT );
@@ -5623,11 +5613,7 @@ case OP_AggStep: {
   assert( pOp->p3>0 && pOp->p3<=(p->nMem-p->nCursor) );
   ctx.pMem = pMem = &aMem[pOp->p3];
   pMem->n++;
-  t.flags = MEM_Null;
-  t.z = 0;
-  t.zMalloc = 0;
-  t.xDel = 0;
-  t.db = db;
+  sqlite3VdbeMemInit(&t, db, MEM_Null);
   ctx.pOut = &t;
   ctx.isError = 0;
   ctx.pColl = 0;
diff --git a/src/vdbe.h b/src/vdbe.h
index ef91010d8..f975f9554 100644
--- a/src/vdbe.h
+++ b/src/vdbe.h
@@ -212,10 +212,10 @@ void sqlite3VdbeSetVarmask(Vdbe*, int);
 int sqlite3MemCompare(const Mem*, const Mem*, const CollSeq*);
 
 void sqlite3VdbeRecordUnpack(KeyInfo*,int,const void*,UnpackedRecord*);
-int sqlite3VdbeRecordCompare(int,const void*,UnpackedRecord*,int);
+int sqlite3VdbeRecordCompare(int,const void*,UnpackedRecord*);
 UnpackedRecord *sqlite3VdbeAllocUnpackedRecord(KeyInfo *, char *, int, char **);
 
-typedef int (*RecordCompare)(int,const void*,UnpackedRecord*,int);
+typedef int (*RecordCompare)(int,const void*,UnpackedRecord*);
 RecordCompare sqlite3VdbeFindCompare(UnpackedRecord*);
 
 #ifndef SQLITE_OMIT_TRIGGER
diff --git a/src/vdbeInt.h b/src/vdbeInt.h
index 27b266986..9c7378a26 100644
--- a/src/vdbeInt.h
+++ b/src/vdbeInt.h
@@ -161,9 +161,6 @@ struct VdbeFrame {
 ** integer etc.) of the same value.
 */
 struct Mem {
-  sqlite3 *db;        /* The associated database connection */
-  char *z;            /* String or BLOB value */
-  double r;           /* Real value */
   union {
     i64 i;              /* Integer value used when MEM_Int is set in flags */
     int nZero;          /* Used when bit MEM_Zero is set in flags */
@@ -171,15 +168,19 @@ struct Mem {
     RowSet *pRowSet;    /* Used only when flags==MEM_RowSet */
     VdbeFrame *pFrame;  /* Used when flags==MEM_Frame */
   } u;
-  int n;              /* Number of characters in string value, excluding '\0' */
   u16 flags;          /* Some combination of MEM_Null, MEM_Str, MEM_Dyn, etc. */
   u8  enc;            /* SQLITE_UTF8, SQLITE_UTF16BE, SQLITE_UTF16LE */
+  int n;              /* Number of characters in string value, excluding '\0' */
+  double r;           /* Real value */
+  char *z;            /* String or BLOB value */
+  char *zMalloc;      /* Dynamic buffer allocated by sqlite3_malloc() */
+  /* ShallowCopy only needs to copy the information above */
+  sqlite3 *db;        /* The associated database connection */
+  void (*xDel)(void*);/* Destructor for Mem.z - only valid if MEM_Dyn */
 #ifdef SQLITE_DEBUG
   Mem *pScopyFrom;    /* This Mem is a shallow copy of pScopyFrom */
   void *pFiller;      /* So that sizeof(Mem) is a multiple of 8 */
 #endif
-  void (*xDel)(void *);  /* If not null, call this function to delete Mem.z */
-  char *zMalloc;      /* Dynamic buffer allocated by sqlite3_malloc() */
 };
 
 /* One or more of the following flags are set to indicate the validOK
@@ -396,8 +397,8 @@ u32 sqlite3VdbeSerialGet(const unsigned char*, u32, Mem*);
 void sqlite3VdbeDeleteAuxData(Vdbe*, int, int);
 
 int sqlite2BtreeKeyCompare(BtCursor *, const void *, int, int, int *);
-int sqlite3VdbeIdxKeyCompare(VdbeCursor*,UnpackedRecord*,int*);
-int sqlite3VdbeIdxRowid(sqlite3*, BtCursor *, i64 *);
+int sqlite3VdbeIdxKeyCompare(sqlite3*,VdbeCursor*,UnpackedRecord*,int*);
+int sqlite3VdbeIdxRowid(sqlite3*, BtCursor*, i64*);
 int sqlite3VdbeExec(Vdbe*);
 int sqlite3VdbeList(Vdbe*);
 int sqlite3VdbeHalt(Vdbe*);
@@ -414,6 +415,7 @@ void sqlite3VdbeMemSetInt64(Mem*, i64);
 #else
   void sqlite3VdbeMemSetDouble(Mem*, double);
 #endif
+void sqlite3VdbeMemInit(Mem*,sqlite3*,u16);
 void sqlite3VdbeMemSetNull(Mem*);
 void sqlite3VdbeMemSetZeroBlob(Mem*,int);
 void sqlite3VdbeMemSetRowSet(Mem*);
@@ -428,11 +430,8 @@ int sqlite3VdbeMemNumerify(Mem*);
 void sqlite3VdbeMemCast(Mem*,u8,u8);
 int sqlite3VdbeMemFromBtree(BtCursor*,u32,u32,int,Mem*);
 void sqlite3VdbeMemRelease(Mem *p);
-void sqlite3VdbeMemReleaseExternal(Mem *p);
 #define VdbeMemDynamic(X)  \
   (((X)->flags&(MEM_Agg|MEM_Dyn|MEM_RowSet|MEM_Frame))!=0)
-#define VdbeMemReleaseExtern(X)  \
-  if( VdbeMemDynamic(X) ) sqlite3VdbeMemReleaseExternal(X);
 int sqlite3VdbeMemFinalize(Mem*, FuncDef*);
 const char *sqlite3OpcodeName(int);
 int sqlite3VdbeMemGrow(Mem *pMem, int n, int preserve);
diff --git a/src/vdbeapi.c b/src/vdbeapi.c
index b64f33c8c..ef1167a52 100644
--- a/src/vdbeapi.c
+++ b/src/vdbeapi.c
@@ -662,8 +662,7 @@ static SQLITE_NOINLINE void *createAggContext(sqlite3_context *p, int nByte){
   Mem *pMem = p->pMem;
   assert( (pMem->flags & MEM_Agg)==0 );
   if( nByte<=0 ){
-    sqlite3VdbeMemReleaseExternal(pMem);
-    pMem->flags = MEM_Null;
+    sqlite3VdbeMemSetNull(pMem);
     pMem->z = 0;
   }else{
     sqlite3VdbeMemGrow(pMem, nByte, 0);
@@ -803,11 +802,21 @@ static const Mem *columnNullValue(void){
 #if defined(SQLITE_DEBUG) && defined(__GNUC__)
     __attribute__((aligned(8))) 
 #endif
-    = {0, "", (double)0, {0}, 0, MEM_Null, 0,
+    = {
+        /* .u          = */ {0},
+        /* .flags      = */ MEM_Null,
+        /* .enc        = */ 0,
+        /* .n          = */ 0,
+        /* .r          = */ (double)0,
+        /* .z          = */ 0,
+        /* .zMalloc    = */ 0,
+        /* .db         = */ 0,
+        /* .xDel       = */ 0,
 #ifdef SQLITE_DEBUG
-       0, 0,  /* pScopyFrom, pFiller */
+        /* .pScopyFrom = */ 0,
+        /* .pFiller    = */ 0,
 #endif
-       0, 0 };
+      };
   return &nullMem;
 }
 
@@ -1184,7 +1193,7 @@ int sqlite3_bind_blob64(
   if( nData>0x7fffffff ){
     return invokeValueDestructor(zData, xDel, 0);
   }else{
-    return bindText(pStmt, i, zData, nData, xDel, 0);
+    return bindText(pStmt, i, zData, (int)nData, xDel, 0);
   }
 }
 int sqlite3_bind_double(sqlite3_stmt *pStmt, int i, double rValue){
@@ -1241,7 +1250,7 @@ int sqlite3_bind_text64(
     return invokeValueDestructor(zData, xDel, 0);
   }else{
     if( enc==SQLITE_UTF16 ) enc = SQLITE_UTF16NATIVE;
-    return bindText(pStmt, i, zData, nData, xDel, enc);
+    return bindText(pStmt, i, zData, (int)nData, xDel, enc);
   }
 }
 #ifndef SQLITE_OMIT_UTF16
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index 3360d919b..8466bfb30 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -3085,7 +3085,6 @@ u32 sqlite3VdbeSerialGet(
       static const u16 aFlag[] = { MEM_Blob|MEM_Ephem, MEM_Str|MEM_Ephem };
       pMem->z = (char *)buf;
       pMem->n = (serial_type-12)/2;
-      pMem->xDel = 0;
       pMem->flags = aFlag[serial_type&1];
       return pMem->n;
     }
@@ -3303,8 +3302,9 @@ static int vdbeCompareMemString(
     int n1, n2;
     Mem c1;
     Mem c2;
-    memset(&c1, 0, sizeof(c1));
-    memset(&c2, 0, sizeof(c2));
+    c1.db = c2.db = pMem1->db;
+    c1.flags = c2.flags = 0;
+    c1.zMalloc = c2.zMalloc = 0;
     sqlite3VdbeMemShallowCopy(&c1, pMem1, MEM_Ephem);
     sqlite3VdbeMemShallowCopy(&c2, pMem2, MEM_Ephem);
     v1 = sqlite3ValueText((sqlite3_value*)&c1, pColl->enc);
@@ -3481,7 +3481,7 @@ static i64 vdbeRecordDecodeInt(u32 serial_type, const u8 *aKey){
 ** pPKey2->errCode is set to SQLITE_NOMEM and, if it is not NULL, the
 ** malloc-failed flag set on database handle (pPKey2->pKeyInfo->db).
 */
-int sqlite3VdbeRecordCompare(
+static int vdbeRecordCompareWithSkip(
   int nKey1, const void *pKey1,   /* Left key */
   UnpackedRecord *pPKey2,         /* Right key */
   int bSkip                       /* If true, skip the first field */
@@ -3663,6 +3663,13 @@ int sqlite3VdbeRecordCompare(
   );
   return pPKey2->default_rc;
 }
+int sqlite3VdbeRecordCompare(
+  int nKey1, const void *pKey1,   /* Left key */
+  UnpackedRecord *pPKey2          /* Right key */
+){
+  return vdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 0);
+}
+
 
 /*
 ** This function is an optimized version of sqlite3VdbeRecordCompare() 
@@ -3675,8 +3682,7 @@ int sqlite3VdbeRecordCompare(
 */
 static int vdbeRecordCompareInt(
   int nKey1, const void *pKey1, /* Left key */
-  UnpackedRecord *pPKey2,       /* Right key */
-  int bSkip                     /* Ignored */
+  UnpackedRecord *pPKey2        /* Right key */
 ){
   const u8 *aKey = &((const u8*)pKey1)[*(const u8*)pKey1 & 0x3F];
   int serial_type = ((const u8*)pKey1)[1];
@@ -3685,9 +3691,7 @@ static int vdbeRecordCompareInt(
   u64 x;
   i64 v = pPKey2->aMem[0].u.i;
   i64 lhs;
-  UNUSED_PARAMETER(bSkip);
 
-  assert( bSkip==0 );
   assert( (*(u8*)pKey1)<=0x3F || CORRUPT_DB );
   switch( serial_type ){
     case 1: { /* 1-byte signed integer */
@@ -3737,10 +3741,10 @@ static int vdbeRecordCompareInt(
     ** (as gcc is clever enough to combine the two like cases). Other 
     ** compilers might be similar.  */ 
     case 0: case 7:
-      return sqlite3VdbeRecordCompare(nKey1, pKey1, pPKey2, 0);
+      return sqlite3VdbeRecordCompare(nKey1, pKey1, pPKey2);
 
     default:
-      return sqlite3VdbeRecordCompare(nKey1, pKey1, pPKey2, 0);
+      return sqlite3VdbeRecordCompare(nKey1, pKey1, pPKey2);
   }
 
   if( v>lhs ){
@@ -3750,7 +3754,7 @@ static int vdbeRecordCompareInt(
   }else if( pPKey2->nField>1 ){
     /* The first fields of the two keys are equal. Compare the trailing 
     ** fields.  */
-    res = sqlite3VdbeRecordCompare(nKey1, pKey1, pPKey2, 1);
+    res = vdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 1);
   }else{
     /* The first fields of the two keys are equal and there are no trailing
     ** fields. Return pPKey2->default_rc in this case. */
@@ -3769,17 +3773,13 @@ static int vdbeRecordCompareInt(
 */
 static int vdbeRecordCompareString(
   int nKey1, const void *pKey1, /* Left key */
-  UnpackedRecord *pPKey2,       /* Right key */
-  int bSkip
+  UnpackedRecord *pPKey2        /* Right key */
 ){
   const u8 *aKey1 = (const u8*)pKey1;
   int serial_type;
   int res;
-  UNUSED_PARAMETER(bSkip);
 
-  assert( bSkip==0 );
   getVarint32(&aKey1[1], serial_type);
-
   if( serial_type<12 ){
     res = pPKey2->r1;      /* (pKey1/nKey1) is a number or a null */
   }else if( !(serial_type & 0x01) ){ 
@@ -3801,7 +3801,7 @@ static int vdbeRecordCompareString(
       res = nStr - pPKey2->aMem[0].n;
       if( res==0 ){
         if( pPKey2->nField>1 ){
-          res = sqlite3VdbeRecordCompare(nKey1, pKey1, pPKey2, 1);
+          res = vdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 1);
         }else{
           res = pPKey2->default_rc;
         }
@@ -3883,8 +3883,6 @@ int sqlite3VdbeIdxRowid(sqlite3 *db, BtCursor *pCur, i64 *rowid){
   u32 lenRowid;     /* Size of the rowid */
   Mem m, v;
 
-  UNUSED_PARAMETER(db);
-
   /* Get the size of the index entry.  Only indices entries of less
   ** than 2GiB are support - anything large must be database corruption.
   ** Any corruption is detected in sqlite3BtreeParseCellPtr(), though, so
@@ -3896,7 +3894,7 @@ int sqlite3VdbeIdxRowid(sqlite3 *db, BtCursor *pCur, i64 *rowid){
   assert( (nCellKey & SQLITE_MAX_U32)==(u64)nCellKey );
 
   /* Read in the complete content of the index entry */
-  memset(&m, 0, sizeof(m));
+  sqlite3VdbeMemInit(&m, db, 0);
   rc = sqlite3VdbeMemFromBtree(pCur, 0, (u32)nCellKey, 1, &m);
   if( rc ){
     return rc;
@@ -3956,6 +3954,7 @@ idx_rowid_corruption:
 ** of the keys prior to the final rowid, not the entire key.
 */
 int sqlite3VdbeIdxKeyCompare(
+  sqlite3 *db,                     /* Database connection */
   VdbeCursor *pC,                  /* The cursor to compare against */
   UnpackedRecord *pUnpacked,       /* Unpacked version of key */
   int *res                         /* Write the comparison result here */
@@ -3974,12 +3973,12 @@ int sqlite3VdbeIdxKeyCompare(
     *res = 0;
     return SQLITE_CORRUPT_BKPT;
   }
-  memset(&m, 0, sizeof(m));
+  sqlite3VdbeMemInit(&m, db, 0);
   rc = sqlite3VdbeMemFromBtree(pC->pCursor, 0, (u32)nCellKey, 1, &m);
   if( rc ){
     return rc;
   }
-  *res = sqlite3VdbeRecordCompare(m.n, m.z, pUnpacked, 0);
+  *res = sqlite3VdbeRecordCompare(m.n, m.z, pUnpacked);
   sqlite3VdbeMemRelease(&m);
   return SQLITE_OK;
 }
diff --git a/src/vdbemem.c b/src/vdbemem.c
index ea4def3f8..359abb891 100644
--- a/src/vdbemem.c
+++ b/src/vdbemem.c
@@ -26,11 +26,10 @@
 ** this:    assert( sqlite3VdbeCheckMemInvariants(pMem) );
 */
 int sqlite3VdbeCheckMemInvariants(Mem *p){
-  /* The MEM_Dyn bit is set if and only if Mem.xDel is a non-NULL destructor
-  ** function for Mem.z 
+  /* If MEM_Dyn is set then Mem.xDel!=0.  
+  ** Mem.xDel is might not be initialized if MEM_Dyn is clear.
   */
   assert( (p->flags & MEM_Dyn)==0 || p->xDel!=0 );
-  assert( (p->flags & MEM_Dyn)!=0 || p->xDel==0 );
 
   /* If p holds a string or blob, the Mem.z must point to exactly
   ** one of the following:
@@ -48,7 +47,6 @@ int sqlite3VdbeCheckMemInvariants(Mem *p){
       ((p->flags&MEM_Static)!=0 ? 1 : 0) == 1
     );
   }
-
   return 1;
 }
 #endif
@@ -121,9 +119,8 @@ int sqlite3VdbeMemGrow(Mem *pMem, int n, int bPreserve){
       pMem->zMalloc = sqlite3DbMallocRaw(pMem->db, n);
     }
     if( pMem->zMalloc==0 ){
-      VdbeMemReleaseExtern(pMem);
+      sqlite3VdbeMemSetNull(pMem);
       pMem->z = 0;
-      pMem->flags = MEM_Null;  
       return SQLITE_NOMEM;
     }
   }
@@ -138,7 +135,6 @@ int sqlite3VdbeMemGrow(Mem *pMem, int n, int bPreserve){
 
   pMem->z = pMem->zMalloc;
   pMem->flags &= ~(MEM_Dyn|MEM_Ephem|MEM_Static);
-  pMem->xDel = 0;
   return SQLITE_OK;
 }
 
@@ -301,7 +297,7 @@ int sqlite3VdbeMemFinalize(Mem *pMem, FuncDef *pFunc){
     ctx.pMem = pMem;
     ctx.pFunc = pFunc;
     pFunc->xFinalize(&ctx); /* IMP: R-24505-23230 */
-    assert( 0==(pMem->flags&MEM_Dyn) && !pMem->xDel );
+    assert( (pMem->flags & MEM_Dyn)==0 );
     sqlite3DbFree(pMem->db, pMem->zMalloc);
     memcpy(pMem, &t, sizeof(t));
     rc = ctx.isError;
@@ -310,29 +306,34 @@ int sqlite3VdbeMemFinalize(Mem *pMem, FuncDef *pFunc){
 }
 
 /*
-** If the memory cell contains a string value that must be freed by
-** invoking an external callback, free it now. Calling this function
-** does not free any Mem.zMalloc buffer.
+** If the memory cell contains a value that must be freed by
+** invoking the external callback in Mem.xDel, then this routine
+** will free that value.  It also sets Mem.flags to MEM_Null.
 **
-** The VdbeMemReleaseExtern() macro invokes this routine if only if there
-** is work for this routine to do.
+** This is a helper routine for sqlite3VdbeMemSetNull() and
+** for sqlite3VdbeMemRelease().  Use those other routines as the
+** entry point for releasing Mem resources.
 */
-void sqlite3VdbeMemReleaseExternal(Mem *p){
+static SQLITE_NOINLINE void vdbeMemClearExternAndSetNull(Mem *p){
   assert( p->db==0 || sqlite3_mutex_held(p->db->mutex) );
+  assert( VdbeMemDynamic(p) );
   if( p->flags&MEM_Agg ){
     sqlite3VdbeMemFinalize(p, p->u.pDef);
     assert( (p->flags & MEM_Agg)==0 );
-    sqlite3VdbeMemRelease(p);
-  }else if( p->flags&MEM_Dyn ){
+    testcase( p->flags & MEM_Dyn );
+  }
+  if( p->flags&MEM_Dyn ){
     assert( (p->flags&MEM_RowSet)==0 );
     assert( p->xDel!=SQLITE_DYNAMIC && p->xDel!=0 );
     p->xDel((void *)p->z);
-    p->xDel = 0;
   }else if( p->flags&MEM_RowSet ){
     sqlite3RowSetClear(p->u.pRowSet);
   }else if( p->flags&MEM_Frame ){
-    sqlite3VdbeMemSetNull(p);
+    VdbeFrame *pFrame = p->u.pFrame;
+    pFrame->pParent = pFrame->v->pDelFrame;
+    pFrame->v->pDelFrame = pFrame;
   }
+  p->flags = MEM_Null;
 }
 
 /*
@@ -340,12 +341,12 @@ void sqlite3VdbeMemReleaseExternal(Mem *p){
 ** by p->xDel and memory in p->zMalloc.
 **
 ** This is a helper routine invoked by sqlite3VdbeMemRelease() in
-** the uncommon case when there really is memory in p that is
-** need of freeing.
+** the unusual case where there really is memory in p that needs
+** to be freed.
 */
-static SQLITE_NOINLINE void vdbeMemRelease(Mem *p){
+static SQLITE_NOINLINE void vdbeMemClear(Mem *p){
   if( VdbeMemDynamic(p) ){
-    sqlite3VdbeMemReleaseExternal(p);
+    vdbeMemClearExternAndSetNull(p);
   }
   if( p->zMalloc ){
     sqlite3DbFree(p->db, p->zMalloc);
@@ -355,18 +356,20 @@ static SQLITE_NOINLINE void vdbeMemRelease(Mem *p){
 }
 
 /*
-** Release any memory held by the Mem. This may leave the Mem in an
-** inconsistent state, for example with (Mem.z==0) and
-** (Mem.flags==MEM_Str).
+** Release any memory resources held by the Mem.  Both the memory that is
+** free by Mem.xDel and the Mem.zMalloc allocation are freed.
+**
+** Use this routine prior to clean up prior to abandoning a Mem, or to
+** reset a Mem back to its minimum memory utilization.
+**
+** Use sqlite3VdbeMemSetNull() to release just the Mem.xDel space
+** prior to inserting new content into the Mem.
 */
 void sqlite3VdbeMemRelease(Mem *p){
   assert( sqlite3VdbeCheckMemInvariants(p) );
   if( VdbeMemDynamic(p) || p->zMalloc ){
-    vdbeMemRelease(p);
-  }else{
-    p->z = 0;
+    vdbeMemClear(p);
   }
-  assert( p->xDel==0 );
 }
 
 /*
@@ -578,20 +581,37 @@ void sqlite3VdbeMemCast(Mem *pMem, u8 aff, u8 encoding){
   }
 }
 
+/*
+** Initialize bulk memory to be a consistent Mem object.
+**
+** The minimum amount of initialization feasible is performed.
+*/
+void sqlite3VdbeMemInit(Mem *pMem, sqlite3 *db, u16 flags){
+  assert( (flags & ~MEM_TypeMask)==0 );
+  pMem->flags = flags;
+  pMem->db = db;
+  pMem->zMalloc = 0;
+}
+
 
 /*
 ** Delete any previous value and set the value stored in *pMem to NULL.
+**
+** This routine calls the Mem.xDel destructor to dispose of values that
+** require the destructor.  But it preserves the Mem.zMalloc memory allocation.
+** To free all resources, use sqlite3VdbeMemRelease(), which both calls this
+** routine to invoke the destructor and deallocates Mem.zMalloc.
+**
+** Use this routine to reset the Mem prior to insert a new value.
+**
+** Use sqlite3VdbeMemRelease() to complete erase the Mem prior to abandoning it.
 */
 void sqlite3VdbeMemSetNull(Mem *pMem){
-  if( pMem->flags & MEM_Frame ){
-    VdbeFrame *pFrame = pMem->u.pFrame;
-    pFrame->pParent = pFrame->v->pDelFrame;
-    pFrame->v->pDelFrame = pFrame;
-  }
-  if( pMem->flags & MEM_RowSet ){
-    sqlite3RowSetClear(pMem->u.pRowSet);
+  if( VdbeMemDynamic(pMem) ){
+    vdbeMemClearExternAndSetNull(pMem);
+  }else{
+    pMem->flags = MEM_Null;
   }
-  MemSetTypeFlag(pMem, MEM_Null);
 }
 void sqlite3ValueSetNull(sqlite3_value *p){
   sqlite3VdbeMemSetNull((Mem*)p); 
@@ -608,14 +628,7 @@ void sqlite3VdbeMemSetZeroBlob(Mem *pMem, int n){
   if( n<0 ) n = 0;
   pMem->u.nZero = n;
   pMem->enc = SQLITE_UTF8;
-
-#ifdef SQLITE_OMIT_INCRBLOB
-  sqlite3VdbeMemGrow(pMem, n, 0);
-  if( pMem->z ){
-    pMem->n = n;
-    memset(pMem->z, 0, n);
-  }
-#endif
+  pMem->z = 0;
 }
 
 /*
@@ -624,7 +637,7 @@ void sqlite3VdbeMemSetZeroBlob(Mem *pMem, int n){
 ** a 64-bit integer.
 */
 static SQLITE_NOINLINE void vdbeReleaseAndSetInt64(Mem *pMem, i64 val){
-  sqlite3VdbeMemReleaseExternal(pMem);
+  sqlite3VdbeMemSetNull(pMem);
   pMem->u.i = val;
   pMem->flags = MEM_Int;
 }
@@ -648,10 +661,8 @@ void sqlite3VdbeMemSetInt64(Mem *pMem, i64 val){
 ** manifest type REAL.
 */
 void sqlite3VdbeMemSetDouble(Mem *pMem, double val){
-  if( sqlite3IsNaN(val) ){
-    sqlite3VdbeMemSetNull(pMem);
-  }else{
-    sqlite3VdbeMemRelease(pMem);
+  sqlite3VdbeMemSetNull(pMem);
+  if( !sqlite3IsNaN(val) ){
     pMem->r = val;
     pMem->flags = MEM_Real;
   }
@@ -730,9 +741,9 @@ void sqlite3VdbeMemAboutToChange(Vdbe *pVdbe, Mem *pMem){
 */
 void sqlite3VdbeMemShallowCopy(Mem *pTo, const Mem *pFrom, int srcType){
   assert( (pFrom->flags & MEM_RowSet)==0 );
-  VdbeMemReleaseExtern(pTo);
+  assert( pTo->db==pFrom->db );
+  if( VdbeMemDynamic(pTo) ) vdbeMemClearExternAndSetNull(pTo);
   memcpy(pTo, pFrom, MEMCELLSIZE);
-  pTo->xDel = 0;
   if( (pFrom->flags&MEM_Static)==0 ){
     pTo->flags &= ~(MEM_Dyn|MEM_Static|MEM_Ephem);
     assert( srcType==MEM_Ephem || srcType==MEM_Static );
@@ -747,12 +758,11 @@ void sqlite3VdbeMemShallowCopy(Mem *pTo, const Mem *pFrom, int srcType){
 int sqlite3VdbeMemCopy(Mem *pTo, const Mem *pFrom){
   int rc = SQLITE_OK;
 
+  assert( pTo->db==pFrom->db );
   assert( (pFrom->flags & MEM_RowSet)==0 );
-  VdbeMemReleaseExtern(pTo);
+  if( VdbeMemDynamic(pTo) ) vdbeMemClearExternAndSetNull(pTo);
   memcpy(pTo, pFrom, MEMCELLSIZE);
   pTo->flags &= ~MEM_Dyn;
-  pTo->xDel = 0;
-
   if( pTo->flags&(MEM_Str|MEM_Blob) ){
     if( 0==(pFrom->flags&MEM_Static) ){
       pTo->flags |= MEM_Ephem;
@@ -777,7 +787,6 @@ void sqlite3VdbeMemMove(Mem *pTo, Mem *pFrom){
   sqlite3VdbeMemRelease(pTo);
   memcpy(pTo, pFrom, sizeof(Mem));
   pFrom->flags = MEM_Null;
-  pFrom->xDel = 0;
   pFrom->zMalloc = 0;
 }
 
@@ -825,7 +834,8 @@ int sqlite3VdbeMemSetStr(
   if( nByte<0 ){
     assert( enc!=0 );
     if( enc==SQLITE_UTF8 ){
-      for(nByte=0; nByte<=iLimit && z[nByte]; nByte++){}
+      nByte = sqlite3Strlen30(z);
+      if( nByte>iLimit ) nByte = iLimit+1;
     }else{
       for(nByte=0; nByte<=iLimit && (z[nByte] | z[nByte+1]); nByte+=2){}
     }
@@ -851,7 +861,6 @@ int sqlite3VdbeMemSetStr(
   }else if( xDel==SQLITE_DYNAMIC ){
     sqlite3VdbeMemRelease(pMem);
     pMem->zMalloc = pMem->z = (char *)z;
-    pMem->xDel = 0;
   }else{
     sqlite3VdbeMemRelease(pMem);
     pMem->z = (char *)z;
@@ -883,8 +892,11 @@ int sqlite3VdbeMemSetStr(
 ** key is true to get the key or false to get data.  The result is written
 ** into the pMem element.
 **
-** The pMem structure is assumed to be uninitialized.  Any prior content
-** is overwritten without being freed.
+** The pMem object must have been initialized.  This routine will use
+** pMem->zMalloc to hold the content from the btree, if possible.  New
+** pMem->zMalloc space will be allocated if necessary.  The calling routine
+** is responsible for making sure that the pMem object is eventually
+** destroyed.
 **
 ** If this routine fails for any reason (malloc returns NULL or unable
 ** to read from the disk) then the pMem is left in an inconsistent state.
@@ -901,6 +913,7 @@ int sqlite3VdbeMemFromBtree(
   int rc = SQLITE_OK; /* Return code */
 
   assert( sqlite3BtreeCursorIsValid(pCur) );
+  assert( !VdbeMemDynamic(pMem) );
 
   /* Note: the calls to BtreeKeyFetch() and DataFetch() below assert() 
   ** that both the BtShared and database handle mutexes are held. */
@@ -913,23 +926,25 @@ int sqlite3VdbeMemFromBtree(
   assert( zData!=0 );
 
   if( offset+amt<=available ){
-    sqlite3VdbeMemRelease(pMem);
     pMem->z = &zData[offset];
     pMem->flags = MEM_Blob|MEM_Ephem;
     pMem->n = (int)amt;
-  }else if( SQLITE_OK==(rc = sqlite3VdbeMemGrow(pMem, amt+2, 0)) ){
-    if( key ){
-      rc = sqlite3BtreeKey(pCur, offset, amt, pMem->z);
-    }else{
-      rc = sqlite3BtreeData(pCur, offset, amt, pMem->z);
-    }
-    if( rc==SQLITE_OK ){
-      pMem->z[amt] = 0;
-      pMem->z[amt+1] = 0;
-      pMem->flags = MEM_Blob|MEM_Term;
-      pMem->n = (int)amt;
-    }else{
-      sqlite3VdbeMemRelease(pMem);
+  }else{
+    pMem->flags = MEM_Null;
+    if( SQLITE_OK==(rc = sqlite3VdbeMemGrow(pMem, amt+2, 0)) ){
+      if( key ){
+        rc = sqlite3BtreeKey(pCur, offset, amt, pMem->z);
+      }else{
+        rc = sqlite3BtreeData(pCur, offset, amt, pMem->z);
+      }
+      if( rc==SQLITE_OK ){
+        pMem->z[amt] = 0;
+        pMem->z[amt+1] = 0;
+        pMem->flags = MEM_Blob|MEM_Term;
+        pMem->n = (int)amt;
+      }else{
+        sqlite3VdbeMemRelease(pMem);
+      }
     }
   }
 
diff --git a/src/vdbesort.c b/src/vdbesort.c
index b9a62bf56..2d7bc8a7a 100644
--- a/src/vdbesort.c
+++ b/src/vdbesort.c
@@ -761,7 +761,7 @@ static int vdbeSorterCompare(
   if( pKey2 ){
     sqlite3VdbeRecordUnpack(pTask->pSorter->pKeyInfo, nKey2, pKey2, r2);
   }
-  return sqlite3VdbeRecordCompare(nKey1, pKey1, r2, 0);
+  return sqlite3VdbeRecordCompare(nKey1, pKey1, r2);
 }
 
 /*
@@ -2517,6 +2517,6 @@ int sqlite3VdbeSorterCompare(
     }
   }
 
-  *pRes = sqlite3VdbeRecordCompare(pVal->n, pVal->z, r2, 0);
+  *pRes = sqlite3VdbeRecordCompare(pVal->n, pVal->z, r2);
   return SQLITE_OK;
 }
diff --git a/src/where.c b/src/where.c
index 5b990fc10..c7cb7bb67 100644
--- a/src/where.c
+++ b/src/where.c
@@ -1913,7 +1913,7 @@ static void whereKeyStats(
   assert( pRec->nField>0 && iCol<pIdx->nSampleCol );
   do{
     iTest = (iMin+i)/2;
-    res = sqlite3VdbeRecordCompare(aSample[iTest].n, aSample[iTest].p, pRec, 0);
+    res = sqlite3VdbeRecordCompare(aSample[iTest].n, aSample[iTest].p, pRec);
     if( res<0 ){
       iMin = iTest+1;
     }else{
@@ -1928,16 +1928,16 @@ static void whereKeyStats(
   if( res==0 ){
     /* If (res==0) is true, then sample $i must be equal to pRec */
     assert( i<pIdx->nSample );
-    assert( 0==sqlite3VdbeRecordCompare(aSample[i].n, aSample[i].p, pRec, 0)
+    assert( 0==sqlite3VdbeRecordCompare(aSample[i].n, aSample[i].p, pRec)
          || pParse->db->mallocFailed );
   }else{
     /* Otherwise, pRec must be smaller than sample $i and larger than
     ** sample ($i-1).  */
     assert( i==pIdx->nSample 
-         || sqlite3VdbeRecordCompare(aSample[i].n, aSample[i].p, pRec, 0)>0
+         || sqlite3VdbeRecordCompare(aSample[i].n, aSample[i].p, pRec)>0
          || pParse->db->mallocFailed );
     assert( i==0
-         || sqlite3VdbeRecordCompare(aSample[i-1].n, aSample[i-1].p, pRec, 0)<0
+         || sqlite3VdbeRecordCompare(aSample[i-1].n, aSample[i-1].p, pRec)<0
          || pParse->db->mallocFailed );
   }
 #endif /* ifdef SQLITE_DEBUG */