From: drh <drh@noemail.net>
Date: Sat, 31 Mar 2012 02:34:35 +0000 (+0000)
Subject: Do more aggressive optimization of the AND operator where one side or the
X-Git-Tag: mountain-lion~3^2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=5fb52caadfe3930efc91d2f04a3adb805732b442;p=thirdparty%2Fsqlite.git

Do more aggressive optimization of the AND operator where one side or the
other is always false.

FossilOrigin-Name: f9a7e179cbbeeab5e57bbf392bef89750215546b
---

diff --git a/manifest b/manifest
index 17608576f1..5e66a79aee 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Avoid\susing\sthe\sOVERLAPPED\sstruct\son\sWinCE.
-D 2012-03-30T16:44:33.303
+C Do\smore\saggressive\soptimization\sof\sthe\sAND\soperator\swhere\sone\sside\sor\sthe\nother\sis\salways\sfalse.
+D 2012-03-31T02:34:35.585
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 2f37e468503dbe79d35c9f6dffcf3fae1ae9ec20
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -135,7 +135,7 @@ F src/complete.c dc1d136c0feee03c2f7550bafc0d29075e36deac
 F src/ctime.c a9c26822515f81ec21588cbb482ca6724be02e33
 F src/date.c 067a81c9942c497aafd2c260e13add8a7d0c7dd4
 F src/delete.c 4c20ea4f6213b3bc1c6a510586864b679946e05e
-F src/expr.c 7e40ea9f6899e31134be3c1b88b8347cf9ec40d7
+F src/expr.c ebb0e2b21379d4ec0c5c2c7c952784cb300c8436
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c 657212460bf5cfd3ae607d12ea62092844c227b5
 F src/func.c c6b3c94320253a35bda43fb69cc292618e3285d6
@@ -515,7 +515,7 @@ F test/fuzzer1.test 69cf1036b92fd3b8e1fd65bef4d7ee3f085c28fb
 F test/fuzzerfault.test ff2282c81797b6a355f0748d8b54c7287c5d2b25
 F test/hook.test 5f3749de6462a6b87b4209b74adf7df5ac2df639
 F test/icu.test 70df4faca133254c042d02ae342c0a141f2663f4
-F test/in.test a7b8a0f43da81cd08645b7a710099ffe9ad1126b
+F test/in.test 5941096407d8c133b9eff15bd3e666624b6cbde3
 F test/in2.test 5d4c61d17493c832f7d2d32bef785119e87bde75
 F test/in3.test 3cbf58c87f4052cee3a58b37b6389777505aa0c0
 F test/in4.test 64f3cc1acde1b9161ccdd8e5bde3daefdb5b2617
@@ -999,7 +999,7 @@ F tool/tostr.awk e75472c2f98dd76e06b8c9c1367f4ab07e122d06
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
 F tool/warnings-clang.sh 9f406d66e750e8ac031c63a9ef3248aaa347ef2a
 F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
-P b34491869c4fb31d2fdd14c94a7db2e1c0e572ba
-R 7c7c91e4f03aba786b8f3e6627280744
-U mistachkin
-Z 7d31e5badb9fd33ec4e58af382112a75
+P 196ca3a8b007b9f792e969893d981f6c5aa2fccc
+R d4cee1bded14d0c2a35aac2c2a8ea01d
+U drh
+Z c8013359e2c16f7dbb75906fb62e335f
diff --git a/manifest.uuid b/manifest.uuid
index aa0af4ede5..360fef573d 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-196ca3a8b007b9f792e969893d981f6c5aa2fccc
\ No newline at end of file
+f9a7e179cbbeeab5e57bbf392bef89750215546b
\ No newline at end of file
diff --git a/src/expr.c b/src/expr.c
index 5e3f1204a1..4751ec91bd 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -484,23 +484,55 @@ Expr *sqlite3PExpr(
   Expr *pRight,           /* Right operand */
   const Token *pToken     /* Argument token */
 ){
-  Expr *p = sqlite3ExprAlloc(pParse->db, op, pToken, 1);
-  sqlite3ExprAttachSubtrees(pParse->db, p, pLeft, pRight);
+  Expr *p;
+  if( op==TK_AND && pLeft && pRight ){
+    /* Take advantage of short-circuit false optimization for AND */
+    p = sqlite3ExprAnd(pParse->db, pLeft, pRight);
+  }else{
+    p = sqlite3ExprAlloc(pParse->db, op, pToken, 1);
+    sqlite3ExprAttachSubtrees(pParse->db, p, pLeft, pRight);
+  }
   if( p ) {
     sqlite3ExprCheckHeight(pParse, p->nHeight);
   }
   return p;
 }
 
+/*
+** Return 1 if an expression must be FALSE in all cases and 0 if the
+** expression might be true.  This is an optimization.  If is OK to
+** return 0 here even if the expression really is always false (a 
+** false negative).  But it is a bug to return 1 if the expression
+** might be true in some rare circumstances (a false positive.)
+**
+** Note that if the expression is part of conditional for a
+** LEFT JOIN, then we cannot determine at compile-time whether or not
+** is it true or false, so always return 0.
+*/
+static int exprAlwaysFalse(Expr *p){
+  int v = 0;
+  if( ExprHasProperty(p, EP_FromJoin) ) return 0;
+  if( !sqlite3ExprIsInteger(p, &v) ) return 0;
+  return v==0;
+}
+
 /*
 ** Join two expressions using an AND operator.  If either expression is
 ** NULL, then just return the other expression.
+**
+** If one side or the other of the AND is known to be false, then instead
+** of returning an AND expression, just return a constant expression with
+** a value of false.
 */
 Expr *sqlite3ExprAnd(sqlite3 *db, Expr *pLeft, Expr *pRight){
   if( pLeft==0 ){
     return pRight;
   }else if( pRight==0 ){
     return pLeft;
+  }else if( exprAlwaysFalse(pLeft) || exprAlwaysFalse(pRight) ){
+    sqlite3ExprDelete(db, pLeft);
+    sqlite3ExprDelete(db, pRight);
+    return sqlite3ExprAlloc(db, TK_INTEGER, &sqlite3IntTokens[0], 0);
   }else{
     Expr *pNew = sqlite3ExprAlloc(db, TK_AND, 0, 0);
     sqlite3ExprAttachSubtrees(db, pNew, pLeft, pRight);
diff --git a/test/in.test b/test/in.test
index 108f35589c..3b23f04bbf 100644
--- a/test/in.test
+++ b/test/in.test
@@ -258,17 +258,29 @@ do_test in-7.5 {
     SELECT a FROM t1 WHERE a IN (5) AND b NOT IN ();
   }
 } {5}
-do_test in-7.6 {
+do_test in-7.6.1 {
   execsql {
     SELECT a FROM ta WHERE a IN ();
   }
 } {}
+do_test in-7.6.2 {
+  db status step
+} {0}
 do_test in-7.7 {
   execsql {
     SELECT a FROM ta WHERE a NOT IN ();
   }
 } {1 2 3 4 6 8 10}
 
+do_test in-7.8.1 {
+  execsql {
+    SELECT * FROM ta LEFT JOIN tb ON (ta.b=tb.b) WHERE ta.a IN ();
+  }
+} {}
+do_test in-7.8.2 {
+  db status step
+} {0}
+
 do_test in-8.1 {
   execsql {
     SELECT b FROM t1 WHERE a IN ('hello','there')