Add the sqlite3VdbeMemClearAndResize() function. Fix a sorting-index

prefilter problem.

FossilOrigin-Name: 987a7a211913b3949da20e43423af376f72a28ba

diff --cc manifest
index 1ced1cbf0537d32d89e5154849ac4c9f11f32f01,786c774f5502267881747734d0de5a266d6e81cc..013d54f55bfa5ea724a266cf8d640bb05498cbe4
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Add\sthe\sMem.szMalloc\selement\sto\sthe\sMem\sobject\sand\suse\sit\sto\skeep\strack\sof\nthe\ssize\sof\sthe\sMem.zMalloc\sallocation.
- D 2014-09-18T21:25:33.845
 -C Make\ssure\sthat\sthe\ssorting-index\spre-filter\srecognizes\sthat\sa\srowid\sreference\nmight\sbe\ssortable.\s\sThis\sfixes\sa\sperformance\sregression.
 -D 2014-09-19T02:01:37.043
++C Add\sthe\ssqlite3VdbeMemClearAndResize()\sfunction.\s\sFix\sa\ssorting-index\nprefilter\sproblem.
++D 2014-09-19T04:42:38.074
  F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
  F Makefile.in cf57f673d77606ab0f2d9627ca52a9ba1464146a
  F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@@ -288,14 -288,14 +288,14 @@@ F src/update.c 729f6f18fc27740591d085e1
  F src/utf.c fc6b889ba0779b7722634cdeaa25f1930d93820c
  F src/util.c 4006c01772bd8d8ac4306d523bbcee41d3e392d8
  F src/vacuum.c 59f03f92bcff57faa6a8ca256eb29ccddfb0614a
- F src/vdbe.c fb490f5b1b2ee2f33f60c7dc678c0d0b70f2e0cb
+ F src/vdbe.c 7bc115e540282b1bfff9b43205cbf6528e6398a6
  F src/vdbe.h 09f5b4e3719fa454f252322b1cdab5cf1f361327
- F src/vdbeInt.h 1ac536d1fa1260d72f81003ff5b283e8f3c40442
- F src/vdbeapi.c e088ed70b6cc42ed68985ab064397ebd452286d6
- F src/vdbeaux.c b3230032238df611aefee5907ea792786362a55d
+ F src/vdbeInt.h f177bed1ec8d4eb5c7089f012aeb95f374745735
+ F src/vdbeapi.c e9e33b59834e3edc8790209765e069874c269d9d
+ F src/vdbeaux.c ecf0bb835f7c809ba8e22ba7d3a587b7a087ac52
  F src/vdbeblob.c 848238dc73e93e48432991bb5651bf87d865eca4
- F src/vdbemem.c 3aea3831a981378368ca058cd8fc700b1982772d
- F src/vdbesort.c 09efa5e5098d1a159cd21f588eb118e4fe87cfde
 -F src/vdbemem.c 0678ba6214a810539e51c6d8f263634d405b990f
++F src/vdbemem.c 5cd963730414a1a6ba53b8b340eba3f46ec2cb1d
+ F src/vdbesort.c 75c66c2fc02d450b67b4816873fba8088feaf12c
  F src/vdbetrace.c 4f29b04edb0cec3d5fcd9b566d9f0e75c8984362
  F src/vtab.c 019dbfd0406a7447c990e1f7bd1dfcdb8895697f
  F src/wal.c 10e7de7ce90865a68153f001a61f1d985cd17983
@@@ -1198,7 -1198,7 +1198,8 @@@ F tool/vdbe_profile.tcl 67746953071a9f8
  F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
  F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
  F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
- P 55879932116d373c95a5f32ec44b53a9c3f4db24
- R 508057a57cef866ce62608d1eb2d9e8e
 -P 5b9b8987797abf7c68d2c3154f6657be9b8b1c8f
 -R 15204d62056b16fb4766540f7ebb9528
++P 9c09ac353df6041808cace41880f4729ee73f5e1 72727b68cd07969165f1f0943cc7e1a265436653
++R a5960c77be61d5e92e67de5776336365
++T +closed 72727b68cd07969165f1f0943cc7e1a265436653
  U drh
- Z 7d8fd1db974daf115bf085d0714b6de9
 -Z d3f0dcf862181fb956350fa4a77ff638
++Z 88c7b85ca090541e4ecff878bb673522

diff --cc manifest.uuid
index 77cd05df09fa857c7e9b96820bbe85eaee8e49ec,06e5229d329c2bc7d8cd23d1a557633a3aaf308f..6dc6c4d0432dec3728b79fdeb2b3b798799d224a
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- 9c09ac353df6041808cace41880f4729ee73f5e1
 -72727b68cd07969165f1f0943cc7e1a265436653
++987a7a211913b3949da20e43423af376f72a28ba

diff --cc src/vdbemem.c
index 4ea28f841f4a6c68249251e65307f8ab83bafcdf,ff9f5b6df58ca28b2ae560fb8bfecac08399b8a0..10c91dfd75318fd662309af9962328010609149a
--- 1/src/vdbemem.c
--- 2/src/vdbemem.c
+++ b/src/vdbemem.c
@@@ -150,6 -150,33 +150,28 @@@ SQLITE_NOINLINE int sqlite3VdbeMemGrow(
    return SQLITE_OK;
  }
  
 -** The pMem->xDel destructor is called, if it exists.
 -**
 -** The value of the pMem after this routine returns might be NULL or
 -** it might retain its prior value, depending on circumstances.  The
 -** caller should make no assumptions about the state of pMem after this
 -** routine returns, except that pMem->zMalloc is at least the requested
 -** size and pMem->z==pMem->zMalloc.
+ /*
+ ** Change the pMem->zMalloc allocation to be at least szNew bytes.
+ ** If pMem->zMalloc already meets or exceeds the requested size, this
+ ** routine is a no-op.
+ **
+ ** Any prior string or blob content in the pMem object may be discarded.
 -  pMem->flags &= ~(MEM_Dyn|MEM_Ephem|MEM_Static);
 -//  pMem->flags = MEM_Null;
++** The pMem->xDel destructor is called, if it exists.  Though MEM_Str
++** and MEM_Blob values may be discarded, MEM_Int, MEM_Real, and MEM_Null
++** values are preserved.
+ **
+ ** Return SQLITE_OK on success or an error code (probably SQLITE_NOMEM)
+ ** if unable to complete the resizing.
+ */
+ int sqlite3VdbeMemClearAndResize(Mem *pMem, int szNew){
+   if( pMem->szMalloc<szNew || (pMem->flags & MEM_Dyn)!=0 ){
+     return sqlite3VdbeMemGrow(pMem, szNew, 0);
+   }
+   pMem->z = pMem->zMalloc;
++  pMem->flags &= (MEM_Null|MEM_Int|MEM_Real);
+   return SQLITE_OK;
+ }
+ 
  /*
  ** Make the given Mem object MEM_Dyn.  In other words, make it so
  ** that any TEXT or BLOB content is stored in memory obtained from