Index: src/where.c
==================================================================
--- src/where.c
+++ src/where.c
@@ -307,10 +307,21 @@
     k = 0;
     pScan->iEquiv++;
   }
   return 0;
 }
+
+/*
+** This is whereScanInit() for the case of an index on an expression.
+** It is factored out into a separate tail-recursion subroutine so that
+** the normal whereScanInit() routine, which is a high-runner, does not
+** need to push registers onto the stack as part of its prologue.
+*/
+static SQLITE_NOINLINE WhereTerm *whereScanInitIndexExpr(WhereScan *pScan){
+  pScan->idxaff = sqlite3ExprAffinity(pScan->pIdxExpr);
+  return whereScanNext(pScan);
+}
 
 /*
 ** Initialize a WHERE clause scanner object.  Return a pointer to the
 ** first match.  Return NULL if there are no matches.
 **
@@ -340,31 +351,33 @@
   pScan->pOrigWC = pWC;
   pScan->pWC = pWC;
   pScan->pIdxExpr = 0;
   pScan->idxaff = 0;
   pScan->zCollName = 0;
+  pScan->opMask = opMask;
+  pScan->k = 0;
+  pScan->aiCur[0] = iCur;
+  pScan->nEquiv = 1;
+  pScan->iEquiv = 1;
   if( pIdx ){
     int j = iColumn;
     iColumn = pIdx->aiColumn[j];
     if( iColumn==XN_EXPR ){
       pScan->pIdxExpr = pIdx->aColExpr->a[j].pExpr;
       pScan->zCollName = pIdx->azColl[j];
+      pScan->aiColumn[0] = XN_EXPR;
+      return whereScanInitIndexExpr(pScan);
     }else if( iColumn==pIdx->pTable->iPKey ){
       iColumn = XN_ROWID;
     }else if( iColumn>=0 ){
       pScan->idxaff = pIdx->pTable->aCol[iColumn].affinity;
       pScan->zCollName = pIdx->azColl[j];
     }
   }else if( iColumn==XN_EXPR ){
     return 0;
   }
-  pScan->opMask = opMask;
-  pScan->k = 0;
-  pScan->aiCur[0] = iCur;
   pScan->aiColumn[0] = iColumn;
-  pScan->nEquiv = 1;
-  pScan->iEquiv = 1;
   return whereScanNext(pScan);
 }
 
 /*
 ** Search for a term in the WHERE clause that is of the form "X <op> <expr>"

Index: test/indexexpr2.test
==================================================================
--- test/indexexpr2.test
+++ test/indexexpr2.test
@@ -247,8 +247,36 @@
 }
 do_execsql_test 5.4 {
   SELECT * FROM t5 WHERE abs(a)=2 or abs(b)=9;
 } {2 4 3 9}
 
+#-------------------------------------------------------------------------
+do_execsql_test 6.0 {
+  CREATE TABLE x1(a INTEGER PRIMARY KEY, b);
+  INSERT INTO x1 VALUES
+      (1, 123), (2, '123'), (3, '123abc'), (4, 123.0), (5, 1234);
+}
+
+do_execsql_test 6.1.1 {
+  SELECT a, b FROM x1 WHERE CAST(b AS INTEGER) = 123;
+} {1 123   2 123   3 123abc  4 123.0}
+do_execsql_test 6.1.2 {
+  CREATE INDEX x1i ON x1( CAST(b AS INTEGER) );
+  SELECT a, b FROM x1 WHERE CAST(b AS INTEGER) = 123;
+} {1 123   2 123   3 123abc  4 123.0}
+do_eqp_test 6.1.3 {
+  SELECT a, b FROM x1 WHERE CAST(b AS INTEGER) = 123;
+} {SEARCH TABLE x1 USING INDEX x1i (<expr>=?)}
+
+do_execsql_test 6.2.1 {
+  SELECT a, b FROM x1 WHERE CAST(b AS TEXT) = 123;
+} {1 123   2 123}
+do_execsql_test 6.2.2 {
+  CREATE INDEX x1i2 ON x1( CAST(b AS TEXT) );
+  SELECT a, b FROM x1 WHERE CAST(b AS TEXT) = 123;
+} {1 123   2 123}
+do_eqp_test 6.2.3 {
+  SELECT a, b FROM x1 WHERE CAST(b AS TEXT) = 123;
+} {SEARCH TABLE x1 USING INDEX x1i2 (<expr>=?)}
 
 
 finish_test