ARROW-7819: [C++][Gandiva] Add DumpIR to Filter/Projector object

[fsaintjacques]

The following patch exposes the generated IR as a method of the objects
for further inspection. This is a breaking change for the internal
method FinalizeModule which doesn't take the dump_ir and optimize
flags, it receives optimize from Configuration now.

• Refactored Engine, notably removed dead code, organized init in a single
  function and simplified LLVMGenerator.
• Dumping IR should not write to stdout, but instead return it as a
  string in the DumpIR method.
• Refactored Types, fixing some bad methods type.
• Added the optimize field to Configuration class.
• Simplified some unit tests.

But more importantly, we can now inspect dynamically:

>>>filter=gandiva.make_filter(table.schema, condition) >>>print(filter.ir)
; ModuleID='codegen'source_filename="codegen"targetdatalayout="e-m:e-i64:64-f80:128-n8:16:32:64-S128"targettriple="x86_64-unknown-linux-gnu"@llvm.global_ctors=appendingglobal [0x { i32, void ()*, i8* }] zeroinitializer@_ZN5arrow7BitUtilL8kBitmaskE=internalunnamed_addrconstant [8xi8] c"\01\02\04\08\10 @\80", align1; FunctionAttrs: norecursenounwinddefinei32 @expr_0_0(i64*nocapturereadonly%args, i64*nocapturereadonly%arg_addr_offsets, i64*nocapturereadnone%local_bitmaps, i16*nocapturereadnone%selection_vector, i64%context_ptr, i64%nrecords) local_unnamed_addr#0 {entry: %0=bitcasti64*%argstoi8**%cond_mem56=loadi8*, i8**%0, align8%1=getelementptri64, i64*%arg_addr_offsets, i643%2=loadi64, i64*%1, align8%a_mem_addr=getelementptri64, i64*%args, i643%3=bitcasti64*%a_mem_addrtodouble**%a_mem7=loaddouble*, double**%3, align8%scevgep=getelementptrdouble, double*%a_mem7, i64%2brlabel%looploop: ; preds=%loop, %entry%loop_var=phii64 [ 0, %entry ], [ %"loop_var+1", %loop ] %scevgep8=getelementptrdouble, double*%scevgep, i64%loop_var%a=loaddouble, double*%scevgep8, align8%4=fcmpoltdouble%a, 1.000000e+03%5=sexti1%4toi8

[github-actions]

https://issues.apache.org/jira/browse/ARROW-7819

[pitrou]

LGTM in general, a few comments.

[pitrou]

Can't we use type_fwd.h instead?

[fsaintjacques]

I tried removing the others and minimizing but it unfolded in too many changes.

[pitrou]

Hmm... can we keep the includes as minimal as possible? Arrow is already slow enough to build.

[fsaintjacques]

clangd has this option to automatically add header when auto-completing. I disabled it.

[projjal]

Looks good to me.

[pravindra]

having the name in stderr is helpful for debugging.

[fsaintjacques]

I recommend to set this in your .gdbinit

set environment GTEST_BREAK_ON_FAILURE=1

Then you run the failing test under gdb, it'll break at the first failing test.

[wesm]

He might mean that the problem may be more evident from looking at test log files :) I think it's OK for now, if it becomes an issue we can improve

[pravindra]

yes, wes - I meant easier to get error from log files or travis output !. but, we'll only hit this when adding new functions - so, it's obvious anyway.