Horton

Re: JIT compiling with LLVM v12.2

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Catalin Iacob <iacobcatalin@gmail.com>
Cc: Stephen Frost <sfrost@snowman.net>, Thomas Munro <thomas.munro@enterprisedb.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-03-21T20:01:05Z
Lists: pgsql-hackers 
Hi,

On 2018-03-21 08:26:28 +0100, Catalin Iacob wrote:
> On Wed, Mar 21, 2018 at 4:07 AM, Andres Freund <andres@anarazel.de> wrote:
> > Indeed. I've pushed a rebased version now, that basically just fixes the
> > issue Thomas observed.
> 
> Testing 2d6f2fba from your repository configured --with-llvm I noticed
> some weird things in the configure output.

Thanks!

> Without --enable-debug:
> configure: using compiler=gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16)
> configure: using CFLAGS=-Wall -Wmissing-prototypes -Wpointer-arith
> -Wdeclaration-after-statement -Wendif-labels
> -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing
> -fwrapv -fexcess-precision=standard -O2
> configure: using CPPFLAGS= -D_GNU_SOURCE
> configure: using LDFLAGS= -L/opt/rh/llvm-toolset-7/root/usr/lib64
> -Wl,--as-needed
> configure: using CXX=g++
> configure: using CXXFLAGS=-Wall -Wpointer-arith -Wendif-labels
> -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing
> -fwrapv -g -O2
> configure: using CLANG=/opt/rh/llvm-toolset-7/root/usr/bin/clang
> configure: using BITCODE_CFLAGS= -fno-strict-aliasing -fwrapv -O2
> configure: using BITCODE_CXXFLAGS= -fno-strict-aliasing -fwrapv -O2
> BITCODE_CXXFLAGS
> 
> With --enable-debug:
> configure: using compiler=gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16)
> configure: using CFLAGS=-Wall -Wmissing-prototypes -Wpointer-arith
> -Wdeclaration-after-statement -Wendif-labels
> -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing
> -fwrapv -fexcess-precision=standard -g -O2
> configure: using CPPFLAGS= -D_GNU_SOURCE
> configure: using LDFLAGS= -L/opt/rh/llvm-toolset-7/root/usr/lib64
> -Wl,--as-needed
> configure: using CXX=g++
> configure: using CXXFLAGS=-Wall -Wpointer-arith -Wendif-labels
> -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing
> -fwrapv -g -g -O2
> configure: using CLANG=/opt/rh/llvm-toolset-7/root/usr/bin/clang
> configure: using BITCODE_CFLAGS= -fno-strict-aliasing -fwrapv -O2
> configure: using BITCODE_CXXFLAGS= -fno-strict-aliasing -fwrapv -O2
> BITCODE_CXXFLAGS
> 
> So I unconditionally get one -g added to CXXFLAGS regardless of
> whether I specify --enable-debug or not. And --enable-debug results in
> -g -g in CXXFLAGS.

Aaah, nice catch.  I was missing an unset CXXFLAGS.


> BTW, you should probably specify -std=c++11 (or whatever you need) as
> various g++ and clang++ versions default to various things. Will the
> required C++ standard be based on the requirements of the C++ code in
> the PG tree or will you take it from LLVM's CXXFLAGS?

It's currently already taken from LLVM's CXXFLAGS if present there, but
just specified for LLVM wrapping files.  Relevant code is in
src/backend/jit/llvm/Makefile:

# All files in this directy link to LLVM.
CFLAGS += $(LLVM_CFLAGS)
CXXFLAGS += $(LLVM_CXXFLAGS)
override CPPFLAGS := $(LLVM_CPPFLAGS) $(CPPFLAGS)
SHLIB_LINK += $(LLVM_LIBS)

Since there's no other C++ code, and I don't forsee anything else, I'm
not planning to set the global CXXFLAGS differently atm. Would just make
it more complicated to use the right flag from llvm's CXXFLAGSS.


> Can --std=c++11 and --std=c++14 compiled .o files be linked together?

Yes, with some limitations. In the PG case all the intra-file calls are
C ABI, there wouldn't be a problem.


> Also, my CXXFLAGS did not get -fexcess-precision=standard neither did
> BITCODE_CFLAGS nor BITCODE_CXXFLAGS.

Yea, that's to be expected, gcc doesn't know that for C++ on most
versions. Some vendors have it patched into.


> 2. Unlike all the other *FLAGS, BITCODE_CXXFLAGS includes itself on
> the right hand side of the equal
> configure: using BITCODE_CXXFLAGS= -fno-strict-aliasing -fwrapv -O2
> BITCODE_CXXFLAGS

Hum, that's definitely a typo bug (missing $ when adding to
BITCODE_CXXFLAGS).


Greetings,

Andres Freund

Commits

  1. Improve JIT docs.

  2. Add documentation for the JIT feature.

  3. Add EXPLAIN support for JIT.

  4. Add inlining support to LLVM JIT provider.

  5. JIT tuple deforming in LLVM JIT provider.

  6. Add FIELDNO_* macro designating offset into structs required for JIT.

  7. Add expression compilation support to LLVM JIT provider.

  8. Expand list of synchronized types and functions in LLVM JIT provider.

  9. Add helpers for emitting LLVM IR.

  10. Basic planner and executor integration for JIT.

  11. Debugging and profiling support for LLVM JIT provider.

  12. Support for optimizing and emitting code in LLVM JIT provider.

  13. Add file containing extensions of the LLVM C API.

  14. Basic JIT provider and error handling infrastructure.

  15. Add configure infrastructure (--with-llvm) to enable LLVM support.

  16. Add C++ support to configure.

  17. Add PGAC_PROG_VARCC_VARFLAGS_OPT autoconf macro.

  18. Fix VM buffer pin management in heap_lock_updated_tuple_rec().

  19. Allow tupleslots to have a fixed tupledesc, use in executor nodes.

  20. Expression evaluation based aggregate transition invocation.

  21. Perform slot validity checks in a separate pass over expression.

  22. Rely on executor utils to build targetlist for DML RETURNING.

  23. Refer to OS X as "macOS", except for the port name which is still "darwin".