Re: JIT compiling with LLVM v12.2 - Mailing list pgsql-hackers

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.

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.

Didn't get to look at the code yet, maybe that comes from:
$ llvm-config --cxxflags
-I/opt/rh/llvm-toolset-7/root/usr/include -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong
--param=ssp-buffer-size=4 -grecord-gcc-switches   -m64 -mtune=generic
-fPIC -fvisibility-inlines-hidden -Wall -W -Wno-unused-parameter
-Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic
-Wno-long-long -Wno-maybe-uninitialized -Wdelete-non-virtual-dtor
-Wno-comment -std=c++11 -ffunction-sections -fdata-sections -O2 -g
-DNDEBUG  -fno-exceptions -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS
-D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS

But on the other hand there are lots of other flags in there that
don't end up in 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? Can --std=c++11
and --std=c++14 compiled .o files be linked together? Or in other
words, in case in the future LLVM starts requiring C++14 but the code
in the PG tree you wrote still builds with C++11, will PG upgrade it's
requirement with LLVM or will it stay with the older standard?

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

In case it's interesting:
$ llvm-config --cflags
-I/opt/rh/llvm-toolset-7/root/usr/include -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong
--param=ssp-buffer-size=4 -grecord-gcc-switches   -m64 -mtune=generic
-fPIC -Wall -W -Wno-unused-parameter -Wwrite-strings
-Wno-missing-field-initializers -pedantic -Wno-long-long -Wno-comment
-ffunction-sections -fdata-sections -O2 -g -DNDEBUG -D_GNU_SOURCE
-D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS


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