Improved comments. Add assert()s to verify that the AggInfo structure

is unchanged after registers have been assigned.

FossilOrigin-Name: 5200b84195ee1ccaa387f7032eae3d463724c48cb53ba0251bbc79e927dd9752

3 files changed, 26 insertions, 3 deletions

diff --git a/src/expr.c b/src/expr.c
index d7f8cfa91..d30ae9766 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -6265,6 +6265,7 @@ static void findOrCreateAggInfoColumn(
   struct AggInfo_col *pCol;
   int k;
 
+  assert( pAggInfo->iFirstReg==0 );
   pCol = pAggInfo->aCol;
   for(k=0; k<pAggInfo->nColumn; k++, pCol++){
     if( pCol->iTable==pExpr->iTable
@@ -6328,6 +6329,7 @@ static int analyzeAggregate(Walker *pWalker, Expr *pExpr){
   AggInfo *pAggInfo = pNC->uNC.pAggInfo;
 
   assert( pNC->ncFlags & NC_UAggInfo );
+  assert( pAggInfo->iFirstReg==0 );
   switch( pExpr->op ){
     default: {
       IndexedExpr *pIEpr;
diff --git a/src/select.c b/src/select.c
index 2e6ad4561..e76198772 100644
--- a/src/select.c
+++ b/src/select.c
@@ -6253,6 +6253,7 @@ static void analyzeAggFuncArgs(
 ){
   int i;
   assert( pAggInfo!=0 );
+  assert( pAggInfo->iFirstReg==0 );
   pNC->ncFlags |= NC_InAggFunc;
   for(i=0; i<pAggInfo->nFunc; i++){
     Expr *pExpr = pAggInfo->aFunc[i].pFExpr;
@@ -6281,6 +6282,7 @@ static void optimizeAggregateUseOfIndexedExpr(
   AggInfo *pAggInfo,      /* The aggregate info */
   NameContext *pNC        /* Name context used to resolve agg-func args */
 ){
+  assert( pAggInfo->iFirstReg==0 );
   pAggInfo->nColumn = pAggInfo->nAccumulator;
   if( ALWAYS(pAggInfo->nSortingColumn>0) ){
     if( pAggInfo->nColumn==0 ){
@@ -6348,6 +6350,18 @@ static void aggregateConvertIndexedExprRefToColumn(AggInfo *pAggInfo){
 ** Allocate a block of registers so that there is one register for each
 ** pAggInfo->aCol[] and pAggInfo->aFunc[] entry in pAggInfo.  The first
 ** register in this block is stored in pAggInfo->iFirstReg.
+**
+** This routine may only be called once for each AggInfo object.  Prior
+** to calling this routine:
+**
+**     *  The aCol[] and aFunc[] arrays may be modified
+**     *  The AggInfoColumnReg() and AggInfoFuncReg() macros may not be used
+**
+** After clling this routine:
+**
+**     *  The aCol[] and aFunc[] arrays are fixed
+**     *  The AggInfoColumnReg() and AggInfoFuncReg() macros may be used
+**
 */
 static void assignAggregateRegisters(Parse *pParse, AggInfo *pAggInfo){
   assert( pAggInfo!=0 );
@@ -6369,6 +6383,7 @@ static void resetAccumulator(Parse *pParse, AggInfo *pAggInfo){
   int i;
   struct AggInfo_func *pFunc;
   int nReg = pAggInfo->nFunc + pAggInfo->nColumn;
+  assert( pAggInfo->iFirstReg>0 );
   assert( pParse->db->pParse==pParse );
   assert( pParse->db->mallocFailed==0 || pParse->nErr!=0 );
   if( nReg==0 ) return;
@@ -6436,6 +6451,7 @@ static void updateAccumulator(
   struct AggInfo_func *pF;
   struct AggInfo_col *pC;
 
+  assert( pAggInfo->iFirstReg>0 );
   pAggInfo->directMode = 1;
   for(i=0, pF=pAggInfo->aFunc; i<pAggInfo->nFunc; i++, pF++){
     int nArg;
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 3ecdb35fe..db65082bb 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -2766,10 +2766,15 @@ struct AggInfo {
 };
 
 /*
-** Macros to compute aCol[] and aFunc[] register numbers:
+** Macros to compute aCol[] and aFunc[] register numbers.
+**
+** These macros should not be used prior to the call to 
+** assignAggregateRegisters() that computes the value of pAggInfo->iFirstReg.
+** The assert()s that are part of this macro verify that constraint.
 */
-#define AggInfoColumnReg(A,I)  ((A)->iFirstReg+(I))
-#define AggInfoFuncReg(A,I)    ((A)->iFirstReg+(A)->nColumn+(I))
+#define AggInfoColumnReg(A,I)  (assert((A)->iFirstReg),(A)->iFirstReg+(I))
+#define AggInfoFuncReg(A,I)    \
+                      (assert((A)->iFirstReg),(A)->iFirstReg+(A)->nColumn+(I))
 
 /*
 ** The datatype ynVar is a signed integer, either 16-bit or 32-bit.