Remove an optimization that can no longer occur, being superceded by the

subquery-reuse optimization.  Put an assert in place of the optimization
to detect if the need for this optimization ever returns.

FossilOrigin-Name: 4fcdc7a2939457e51aab37cab168677cd7f464a9a0aff4f8981e864a30828b3b

manifest

@@ -1,5 +1,5 @@
-C Merge\senhancements\sand\sbug\sfixes\sfrom\strunk.
-D 2018-12-31T18:30:41.155
+C Remove\san\soptimization\sthat\scan\sno\slonger\soccur,\sbeing\ssuperceded\sby\sthe\nsubquery-reuse\soptimization.\s\sPut\san\sassert\sin\splace\sof\sthe\soptimization\nto\sdetect\sif\sthe\sneed\sfor\sthis\soptimization\sever\sreturns.
+D 2018-12-31T20:13:12.301
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in d8b254f8bb81bab43c340d70d17dc3babab40fcc8a348c8255881f780a45fee6
@@ -510,7 +510,7 @@ F src/printf.c 0f1177cf1dd4d7827bf64d840768514ec76409abecaca9e8b577dbd065150381
 F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
 F src/resolve.c 72fe8cae7326b979e7258ab4c531956951e1a5f3fe8644c646abaec1b2eb6d95
 F src/rowset.c d977b011993aaea002cab3e0bb2ce50cf346000dff94e944d547b989f4b1fe93
-F src/select.c 2493d09401fdd3c0b9a8d5b15486876f9167f87ef8013d58be9730f4c83bdb0c
+F src/select.c 4b0be1bfd2d8668e2711f877682361e06b412c53ce7a56303f1f6978ec33eca8
 F src/shell.c.in 207da30342db0b6fac8b2487abd60b059a5ea80cc9494bd1db76a1dd4aae7cca
 F src/sqlite.h.in b54cd42d2f3b739a00de540cafe2dcd0de3b8e1748a2db33a68def487e9e602f
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
@@ -1795,7 +1795,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 0f1b9ff9e1e6f13e03045fcb7d0907227085054f9eb0b0b8471fb26b0094b13a f856676c8438dbf52d299e78f6dd6148d929755dc05cdcabafd17d9a86439435
-R 3d5a1ea78142c180da83ac42547c771a
+P 9fb646f29c05bca5f677a2c7c4f45c36bfe0a0c6a88cb7968b4a0459bdd63bb2
+R ec7392f6deec1d23ad92b0971adf7e38
 U drh
-Z 030784c6ac18d793a85199580bd539ae
+Z 4914e9d7733cf56aae5640f097ed4039

manifest.uuid

@@ -1 +1 @@
-9fb646f29c05bca5f677a2c7c4f45c36bfe0a0c6a88cb7968b4a0459bdd63bb2
+4fcdc7a2939457e51aab37cab168677cd7f464a9a0aff4f8981e864a30828b3b

src/select.c

@@ -5835,22 +5835,12 @@ int sqlite3Select(
     pSub = pItem->pSelect;
     if( pSub==0 ) continue;
 
-    /* Sometimes the code for a subquery will be generated more than
-    ** once, if the subquery is part of the WHERE clause in a LEFT JOIN,
-    ** for example.  In that case, do not regenerate the code to manifest
-    ** a view or the co-routine to implement a view.  The first instance
-    ** is sufficient, though the subroutine to manifest the view does need
-    ** to be invoked again. */
-    if( pItem->addrFillSub ){
-      if( pItem->fg.viaCoroutine==0 ){
-        /* The subroutine that manifests the view might be a one-time routine,
-        ** or it might need to be rerun on each iteration because it
-        ** encodes a correlated subquery. */
-        testcase( sqlite3VdbeGetOp(v, pItem->addrFillSub)->opcode==OP_Once );
-        sqlite3VdbeAddOp2(v, OP_Gosub, pItem->regReturn, pItem->addrFillSub);
-      }
-      continue;
-    }
+    /* The code for a subquery should only be generated once, though it is
+    ** technically harmless for it to be generated multiple times. The
+    ** following assert() will detect if something changes to cause
+    ** the same subquery to be coded multiple times, as a signal to the
+    ** developers to try to optimize the situation. */
+    assert( pItem->addrFillSub==0 );
 
     /* Increment Parse.nHeight by the height of the largest expression
     ** tree referred to by this, the parent select. The child select