Note: We don't alien node elimination when there is an explain codegen
or explain analyze codegen query in master.

  * Skip generating ExecEvalExpr ScanNodes when ProjInfo is a Var list
  * Skip generating SlotGetAttr in AggNodes

This will aid tremendously in debugging codegen because the generated IR
will be easily available to be seen. Rest of the functionality of
EXPLAIN is maintained. Also we only perform the compilation step if it
not a EXPLAIN-only query. That is EXPLAIN CODEGEN with perform code
generation only and will not compile the resultant code. EXPLAIN ANALYZE
will do both, and also execute the query.

ExprTreeGeneratorInfo object keeps track of metadata information
needed to generate code for expression trees.
Refactor ExprTreeGenerators to always use econtext->ecxt_scantuple to
generate the functions. We also have an extra slot_check block to fall
back if it is called with a different slot - which shouldn't happen for
Agg and Scan nodes.

This closes #874

Signed-off-by: NKarthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>

Verify that input expression is of type VAR <= CONST
Codegen expression evaluation
Fix wrong return value type
Support constants and variables of Date type
Add comments and fix code style

This reverts commit aae0ad3d.

This is also transient information, only valid during execution, and should
not be cached with the plan.

This commit generates code for a naive code-generated version of ExecQual that simply fallbacks to regular ExecQual.
The code-generated ExecQual is enrolled in the existing codegen framework and is called only in ExecScan.
After the implementation of the function (i.e., generate code for expression evaluation), we can replace all calls to regular ExecQual with call_ExecQual macros.

This commit  generates code for code path: ExecVariableList > slot_getattr > _slot_getsomeattrs > slot_deform_tuple. This code path is executed during scan in simple select queries that do not have a where clause (e.g., select bar from foo;).

For each attribute A in the target list, regular implementation of ExecvariableList retrieves the slot that A comes from and calls slot_getattr. slot_get_attr() will eventually call slot_deform_tuple (through _slot_getsomeattrs), which fetches all yet unread attributes of the slot until the given attribute.

This commit generates the code for the case that all the attributes in target list use the same slot (created during a scan i.e, ecxt_scantuple). Moreover, instead of looping over the target list one at a time, it uses slot_getattr only once, with the largest attribute index from the target list.

If during code generation time, the completion is not possible (e.g., attributes use different slots), then function returns false and codegen manager will be responsible to manage the clean up.

This implementation does not support:
* Null attributes
* Variable length attributes
* Fixed length attributes passed by reference (e.g., uuid)
If at execution time, we see any of the above types of attributes, we fall back to the regular function.

Moreover, this commit:
* renames existing "codegen" guc, which is used for initiating llvm libraries, to "init_codegen" (Note: we set this guc in gpconfig),
* adds guc "codegen", which enables code generation and compilation at query execution time,
* enhances the existing code generation utilities by adding a function that creates all IR instructions for falling back to regular functions, and
* removes the existing code that generates the code of a naive slot_deform_tuple, which simply falls back to regular slot_deform_tuple.
Signed-off-by: NNikos Armenatzoglou <nikos.armenatzoglou@gmail.com>

tuple.
This closes #649

Squashed commit of the following:

commit 96f415bc1744533e96a74bcc85016ff5df65d06e
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Thu Apr 21 15:08:49 2016 -0700

    Don't call prepare for execution if no generator is registered

commit 5318e9214a3bbc237c0d79017cdef02538c4e711
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Thu Apr 21 11:35:22 2016 -0700

    Adding if codegen protection in starting active manager and while
    deleting manager

commit 12b0045d51a5b056b32a6cc9ef370e6d9af315fd
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Fri Apr 15 14:33:55 2016 -0700

    Updating Readme for Codegen GPDB Function

commit d17119c5d8ce9a706b3321d5e7ad41f419fddbdc
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Wed Apr 13 13:25:14 2016 -0700

    Add documentation for how to codegen in README.md

commit d711be4bb044592e7f97bf31ceb5f32337ad6d03
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Wed Apr 13 11:19:03 2016 -0700

    Fixing doxygen namespace addtogroup

commit e34131bcc9bb3d36c5e8995e1a0efe11fbd55417
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Wed Apr 13 11:17:32 2016 -0700

    Changing CodeGen to Codegen

commit bedfcca80b5f1ff796783ca7c2035d920ae86c4e
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Wed Apr 13 10:51:39 2016 -0700

    Fix cpplint error

commit 32f89feedba655e1242529c78a54faf01ddf32bf
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Wed Apr 13 10:48:49 2016 -0700

    Change regular version of generated to regular version of target in comment

commit d1da2824c08e34eb7139b08cd9d2aff19bf008e7
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Wed Apr 13 10:42:09 2016 -0700

    Made GetFunctionPointer and CreateFunction to take typedef of function type as only public api

commit 9f48f77bd9fc50c7d29a4e8f7700452ef88dc79f
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Tue Apr 12 17:18:24 2016 -0700

    Rename doCodegeneration to GenerateCodeInternal

commit 9884d07f4c6ab08d9ccca8d07b80974081cda1fa
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Tue Apr 12 17:15:55 2016 -0700

    fix cpplint error

commit c21b3bee3e289675fc13017688269b40e26efa11
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Tue Apr 12 17:08:16 2016 -0700

    Update comments

commit f016bb582af65e84def1b55917017008e292d45b
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Tue Apr 12 17:01:19 2016 -0700

    Adding assert in static setToRegular function

commit 93a791a4ec415313933dd5b7c1ae17dbdd6193a6
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Tue Apr 12 16:49:15 2016 -0700

    Removing decltype in Slotdeformtype codegen since we know the functype

commit ed95193d0991cb24fd68f6d9a473de630f297b0c
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Tue Apr 12 16:45:49 2016 -0700

    Fixed compiler / unit test failure
    Changed InitCodeGen to InitCodegen

commit 3c95c9efdd4336e100a86748b0e87d79f07bcc11
Author: Karthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Date:   Tue Apr 12 16:28:24 2016 -0700

    Changing CodeGen back to Codegen while cherry-picking

commit 4e24ef22bcf54edc00c2a0d1f9f9703364cdf5ba
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Tue Apr 12 11:08:42 2016 -0700

    Changing auto to actual type

commit 1d92fc190dda3ec866edc83d56d9eca9fe90a63a
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Tue Apr 12 10:44:49 2016 -0700

    fix indent in codegen_utils

commit ea6fa787a2332f94b8d20d24825ba1f0a240d02e
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 17:25:53 2016 -0700

    Adding codegen guc to wrapper function so related function not executed when codegen guc is disabled

commit f1cd7d80d8d81f3565f3ab12cb94a3c4cc58c44a
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 17:13:24 2016 -0700

    Changing bool to unsigned int in codegen_wrapper.h

commit 7ef462540a312d077b332c732c125c55dedb6b14
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 16:59:08 2016 -0700

    Fix based on lint complain

commit ddc55cec0d579a03cb9e2303efa6d74f5183979f
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 16:19:48 2016 -0700

    Removing commented code from unittest

commit 28b8886ed2bfdc854aa38f871a41536c1e6cef29
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 16:17:45 2016 -0700

    Chaging auto in for to actual type

commit ad8d78e07e9b789f4d8ae3c6ccc3cea1a05089c0
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 16:13:21 2016 -0700

    * Handle return value of SetToGenerated from PrepareForExecution
    * Change size_t to unsigned integer

commit d46ee8be414b3ac2a9ea7ef899f29cef3df145c7
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 15:30:40 2016 -0700

    Introducing template function to do enroll for any type of generator

commit 83428605f906e28d0fc994dcc311e0cc3e6d9e12
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 14:41:11 2016 -0700

    Changing manager to take module name as argument

commit b88aa40f89860e7c15503365ea304d2392f71cda
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 14:27:31 2016 -0700

    adding more comments to SlotDeformTupleCodeGenInfo and unique counter

commit df1b704548fcbc1b43524064eb2f024995eea865
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 14:08:34 2016 -0700

    Change test target to have ext .t and adding gitignore for that extension

commit 9ee3521ca687c4ea7f13d15893f47146ecdb5277
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 13:59:57 2016 -0700

    Add target_include_directories for test library header file

commit effb7dc165b4c7094731dc39e0872741b28b2e6a
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Mon Apr 11 13:36:50 2016 -0700

    Move all possible ifdef from gpdb to codegen_wrapper based on pull request comments

commit 989b96a91c1e843577b5f24623d1e4a6b810394c
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Fri Apr 8 10:43:17 2016 -0700

    fixing comments for GetOrigFuncName in codegen_interface

commit 665de065c34ea13abcec8c5f3a3336558dae501f
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Fri Apr 8 10:27:31 2016 -0700

    Disabling codegen guc by default

commit ec34513e86dea95bd36ee528724273c1c19e7062
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Thu Apr 7 16:28:43 2016 -0700

    Fixed comments space/tab so it aligned in different editor

commit 35a60fe2fd053a5babd1820302afad95c5c2635f
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Thu Apr 7 16:12:08 2016 -0700

    Fixing coding style based on cpplint

commit 9477dcf6c0a7ffcca77b9f2c62c7340d13f474aa
Author: Karthikeyan Jambu Rajaraman <krajaraman@pivotal.io>
Date:   Thu Apr 7 13:37:01 2016 -0700

    Adding USE_CODEGEN ifdef

commit 142ffc1416341a3ac1d0fe37a83577168f2ec166
Author: Shreedhar Hardikar <shardikar@pivotal.io>
Date:   Tue Apr 5 22:21:19 2016 +0000

    Make codegen work with GPDB unit test framework

commit 9dca9507dd933a5517bee3ca34615c09c23c1728
Author: Shreedhar Hardikar <shardikar@pivotal.io>
Date:   Mon Apr 4 22:10:21 2016 +0000

    Add gpcodegen_mock.c

commit 41d515ff0342d3df3b0853ad91731f6d1d75843c
Author: Shreedhar Hardikar <shardikar@pivotal.io>
Date:   Mon Apr 4 21:46:34 2016 +0000

    Remove unneccessary header file includes in codegen

commit 14c5e14b9834197693b1ef56efa96386cfe049c5
Author: Foyzur Rahman <frahman@gmail.com>
Date:   Tue Apr 12 14:49:51 2016 -0700

    Integrate codegen framework and make simple external call to slot deform tuple
Signed-off-by: NKarthikeyan Jambu Rajaraman <karthi.jrk@gmail.com>
Signed-off-by: NFoyzur Rahman <frahman@gmail.com>

parent query's EState.  Now that there's a single flat rangetable for both
the main plan and subplans, there's no need anymore for a separate EState,
and removing it allows cleaning up some crufty code in nodeSubplan.c and
nodeSubqueryscan.c.  Should be a tad faster too, although any difference
will probably be hard to measure.  This is the last bit of subsidiary
mop-up work from changing to a flat rangetable.

back-stamped for this.

(e.g. "INSERT ... VALUES (...), (...), ...") and elsewhere as allowed
by the spec. (e.g. similar to a FROM clause subselect). initdb required.
Joe Conway and Tom Lane.

because node timing is much less predictable than the patch expects.  I kept
the API change for InstrStopNode, however.

Martijn van Oosterhout

bits indicating which optional capabilities can actually be exercised
at runtime.  This will allow Sort and Material nodes, and perhaps later
other nodes, to avoid unnecessary overhead in common cases.
This commit just adds the infrastructure and arranges to pass the correct
flag values down to plan nodes; none of the actual optimizations are here
yet.  I'm committing this separately in case anyone wants to measure the
added overhead.  (It should be negligible.)

Simon Riggs and Tom Lane

scans, using in-memory tuple ID bitmaps as the intermediary.  The planner
frontend (path creation and cost estimation) is not there yet, so none
of this code can be executed.  I have tested it using some hacked planner
code that is far too ugly to see the light of day, however.  Committing
now so that the bulk of the infrastructure changes go in before the tree
drifts under me.

return just a single tuple at a time.  Currently the only such node
type is Hash, but I expect we will soon have indexscans that can return
tuple bitmaps.  A side benefit is that EXPLAIN ANALYZE now shows the
correct tuple count for a Hash node.

ExecProcNode() with a NULL value, so the test couldn't do anything
for us except maybe mask bugs.  Removing it probably doesn't save
anything much either, but then again this is a hot-spot routine.

executing a statement that fires triggers.  Formerly this time was
included in "Total runtime" but not otherwise accounted for.
As a side benefit, we avoid re-opening relations when firing non-deferred
AFTER triggers, because the trigger code can re-use the main executor's
ResultRelInfo data structure.

Tag appropriate files for rc3

Also performed an initial run through of upgrading our Copyright date to
extend to 2005 ... first run here was very simple ... change everything
where: grep 1996-2004 && the word 'Copyright' ... scanned through the
generated list with 'less' first, and after, to make sure that I only
picked up the right entries ...

formerly used in execMain. Since that is no longer the case, this patch
renames ExecProcAppend() to ExecAppend() for the sake of consistency.

In the past, we used a 'Lispy' linked list implementation: a "list" was
merely a pointer to the head node of the list. The problem with that
design is that it makes lappend() and length() linear time. This patch
fixes that problem (and others) by maintaining a count of the list
length and a pointer to the tail node along with each head node pointer.
A "list" is now a pointer to a structure containing some meta-data
about the list; the head and tail pointers in that structure refer
to ListCell structures that maintain the actual linked list of nodes.

The function names of the list API have also been changed to, I hope,
be more logically consistent. By default, the old function names are
still available; they will be disabled-by-default once the rest of
the tree has been updated to use the new API names.

have been there to start with, except for overly enthusiastic copy-and-
paste ...

$Header: -> $PostgreSQL Changes ...