Work toward reducing the incremental size of an ExprList object to 24-byte

per entry, from 32-bytes (on a 64-bit machine).  This helps the new
mini-lookaside allocator to run better by avoiding excessive reallocs.
The current change mostly works, but still has a few loose ends to tie up.
This check-in is merely a snapshot to save my work.

FossilOrigin-Name: fdda76cfb01bf2b19522ac4558b443634d28a69b0828677c42682b645eae1f3b

1 files changed, 21 insertions, 9 deletions

diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 3de659f79..7425b2988 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -2650,23 +2650,28 @@ struct Expr {
 ** also be used as the argument to a function, in which case the a.zName
 ** field is not used.
 **
-** By default the Expr.zSpan field holds a human-readable description of
-** the expression that is used in the generation of error messages and
-** column labels.  In this case, Expr.zSpan is typically the text of a
-** column expression as it exists in a SELECT statement.  However, if
-** the bSpanIsTab flag is set, then zSpan is overloaded to mean the name
-** of the result column in the form: DATABASE.TABLE.COLUMN.  This later
-** form is used for name resolution with nested FROM clauses.
+** In order to try to keep memory usage down, the Expr.a.zEName field
+** is used for multiple purposes:
+**
+**     bNameIsTab    bNameIsSpan        Usage
+**     ----------    -----------        -------------------------
+**       false          false           (1) the AS of result set column
+**                                      (2) COLUMN= of an UPDATE
+**
+**       true           false           DB.TABLE.NAME used to resolve names
+**                                      of subqueries
+**
+**       false          true            Text of the original result set
+**                                      expression.
 */
 struct ExprList {
   int nExpr;             /* Number of expressions on the list */
   struct ExprList_item { /* For each expression in the list */
     Expr *pExpr;            /* The parse tree for this expression */
     char *zEName;           /* Token associated with this expression */
-    char *zSpan;            /* Original text of the expression */
     u8 sortFlags;           /* Mask of KEYINFO_ORDER_* flags */
+    unsigned eEName :2;     /* Meaning of zEName */
     unsigned done :1;       /* A flag to indicate when processing is finished */
-    unsigned bSpanIsTab :1; /* zSpan holds DB.TABLE.COLUMN */
     unsigned reusable :1;   /* Constant expression is reusable */
     unsigned bSorterRef :1; /* Defer evaluation until after sorting */
     unsigned bNulls: 1;     /* True if explicit "NULLS FIRST/LAST" */
@@ -2681,6 +2686,13 @@ struct ExprList {
 };
 
 /*
+** Allowed values for Expr.a.eEName
+*/
+#define ENAME_NAME  0       /* The AS clause of a result set */
+#define ENAME_SPAN  1       /* Complete text of the result set expression */
+#define ENAME_TAB   2       /* "DB.TABLE.NAME" for the result set */
+
+/*
 ** An instance of this structure can hold a simple list of identifiers,
 ** such as the list "a,b,c" in the following statements:
 **