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Adjustments to the implementation of LIMIT so that it uses fewer opcodes.

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FossilOrigin-Name: 39d5b292d27faf00ab58ff4074f91f7aea97cd99
This commit is contained in:
drh
2009-11-12 03:13:26 +00:00
parent ae2a348dbd
commit 9b918ed1d8
4 changed files with 31 additions and 22 deletions
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25
src/select.c
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@@ -681,8 +681,7 @@ static void selectInnerLoop(
if( p->iLimit ){
assert( pOrderBy==0 ); /* If there is an ORDER BY, the call to
** pushOntoSorter() would have cleared p->iLimit */
sqlite3VdbeAddOp2(v, OP_AddImm, p->iLimit, -1);
sqlite3VdbeAddOp2(v, OP_IfZero, p->iLimit, iBreak);
sqlite3VdbeAddOp3(v, OP_IfZero, p->iLimit, iBreak, -1);
}
}
@@ -1308,7 +1307,7 @@ static void computeLimitRegisters(Parse *pParse, Select *p, int iBreak){
Vdbe *v = 0;
int iLimit = 0;
int iOffset;
int addr1;
int addr1, n;
if( p->iLimit ) return;
/*
@@ -1323,10 +1322,19 @@ static void computeLimitRegisters(Parse *pParse, Select *p, int iBreak){
p->iLimit = iLimit = ++pParse->nMem;
v = sqlite3GetVdbe(pParse);
if( NEVER(v==0) ) return; /* VDBE should have already been allocated */
sqlite3ExprCode(pParse, p->pLimit, iLimit);
sqlite3VdbeAddOp1(v, OP_MustBeInt, iLimit);
VdbeComment((v, "LIMIT counter"));
sqlite3VdbeAddOp2(v, OP_IfZero, iLimit, iBreak);
if( sqlite3ExprIsInteger(p->pLimit, &n) ){
if( n==0 ){
sqlite3VdbeAddOp2(v, OP_Goto, 0, iBreak);
}else{
sqlite3VdbeAddOp2(v, OP_Integer, n, iLimit);
VdbeComment((v, "LIMIT counter"));
}
}else{
sqlite3ExprCode(pParse, p->pLimit, iLimit);
sqlite3VdbeAddOp1(v, OP_MustBeInt, iLimit);
VdbeComment((v, "LIMIT counter"));
sqlite3VdbeAddOp2(v, OP_IfZero, iLimit, iBreak);
}
if( p->pOffset ){
p->iOffset = iOffset = ++pParse->nMem;
pParse->nMem++; /* Allocate an extra register for limit+offset */
@@ -1881,8 +1889,7 @@ static int generateOutputSubroutine(
/* Jump to the end of the loop if the LIMIT is reached.
*/
if( p->iLimit ){
sqlite3VdbeAddOp2(v, OP_AddImm, p->iLimit, -1);
sqlite3VdbeAddOp2(v, OP_IfZero, p->iLimit, iBreak);
sqlite3VdbeAddOp3(v, OP_IfZero, p->iLimit, iBreak, -1);
}
/* Generate the subroutine return