Add the OP_ZeroOrNull opcode and use it to compute boolean values for

scalar comparisons, rather than the SQLITE_STOREP2 parameter to the comparison
opcode.

FossilOrigin-Name: 93781b6f10a94fb273204b95156a8b90e07071f28c89e7966c659a0f44f60e98

src/expr.c

@@ -4054,9 +4054,15 @@ expr_code_doover:
       }else{
         r1 = sqlite3ExprCodeTemp(pParse, pLeft, &regFree1);
         r2 = sqlite3ExprCodeTemp(pParse, pExpr->pRight, &regFree2);
-        codeCompare(pParse, pLeft, pExpr->pRight, op,
-            r1, r2, inReg, SQLITE_STOREP2 | p5,
+        sqlite3VdbeAddOp2(v, OP_Integer, 1, inReg);
+        codeCompare(pParse, pLeft, pExpr->pRight, op, r1, r2,
+            sqlite3VdbeCurrentAddr(v)+2, p5,
             ExprHasProperty(pExpr,EP_Commuted));
+        if( p5==SQLITE_NULLEQ ){
+          sqlite3VdbeAddOp2(v, OP_Integer, 0, inReg);
+        }else{
+          sqlite3VdbeAddOp3(v, OP_ZeroOrNull, r1, inReg, r2);
+        }
         assert(TK_LT==OP_Lt); testcase(op==OP_Lt); VdbeCoverageIf(v,op==OP_Lt);
         assert(TK_LE==OP_Le); testcase(op==OP_Le); VdbeCoverageIf(v,op==OP_Le);
         assert(TK_GT==OP_Gt); testcase(op==OP_Gt); VdbeCoverageIf(v,op==OP_Gt);

src/vdbe.c

@@ -2502,6 +2502,24 @@ case OP_IsNull: {            /* same as TK_ISNULL, jump, in1 */
   break;
 }
 
+/* Opcode: ZeroOrNull P1 P2 P3 * *
+** Synopsis: r[P2] = (P1,P3 NOT NULL) ? 0 : NULL;
+**
+** If both registers P1 and P3 are NOT NULL, then store a zero in
+** register P2.  If either register P1 or register P3 or both contain
+** a NULL then store a NULL in register P2.
+*/
+case OP_ZeroOrNull: {            /* in1, out2, in3 */
+  if( (aMem[pOp->p1].flags & MEM_Null)!=0
+   || (aMem[pOp->p3].flags & MEM_Null)!=0
+  ){
+    sqlite3VdbeMemSetNull(aMem + pOp->p2);
+  }else{
+    sqlite3VdbeMemSetInt64(aMem + pOp->p2, 0);
+  }
+  break;
+}
+
 /* Opcode: NotNull P1 P2 * * *
 ** Synopsis: if r[P1]!=NULL goto P2
 **