[interpreter] Drop IncrementalExecutor offsets to obtain LLJIT for Cling

[aaronj0]

This patch drops pointer arithmetic used to obtain the llvm::orc::LLJIT from older Cling versions. This would make for safer usage of the cling::Interpreter and good to have for the 1.7.0 stable release that ROOT will move to.

[mcbarton]

@aaronj0 When I was looking at this in my PR to drop cling 1.0 support I was planning to replace every occurance of compat::getExecutionEngine in the code (given its now just a return statement). I just never got around to doing it. Maybe you can do it here?

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.43%. Comparing base (fd69d55) to head (3e80d55).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #589   +/-   ##
=======================================
  Coverage   76.43%   76.43%           
=======================================
  Files           9        9           
  Lines        3666     3666           
=======================================
  Hits         2802     2802           
  Misses        864      864           

Files with missing lines	Coverage Δ
lib/Interpreter/Compatibility.h	91.96% <ø> (ø)

Files with missing lines	Coverage Δ
lib/Interpreter/Compatibility.h	91.96% <ø> (ø)

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[mcbarton]

@aaronj0 Given v1.7.0 just got released without this, do you mind me just doing this patch as part of my PR as part of my effort to drop cling 1.0 support here #581 ?

[aaronj0]

@aaronj0 Given v1.7.0 just got released without this, do you mind me just doing this patch as part of my PR as part of my effort to drop cling 1.0 support here #581 ?

I prefer to land this here as an atomic change...

@aaronj0 When I was looking at this in my PR to drop cling 1.0 support I was planning to replace every occurance of compat::getExecutionEngine in the code (given its not just a return statement). I just never got around to doing it. Maybe you can do it here?

hmm that doesn't make sense to me:

In a function that accepts a compat::Interpreter :

CppInterOp/lib/Interpreter/CppInterOp.cpp

Lines 3160 to 3162 in 392b754

	bool InsertOrReplaceJitSymbol(compat::Interpreter& I,
	const char* linker_mangled_name,
	uint64_t address) {

That uses this API:

CppInterOp/lib/Interpreter/CppInterOp.cpp

Lines 3212 to 3217 in 392b754

	// Let's inject it.
	llvm::orc::SymbolMap InjectedSymbols;
	auto& DL = compat::getExecutionEngine(I)->getDataLayout();
	char GlobalPrefix = DL.getGlobalPrefix();
	std::string tmp(linker_mangled_name);

we need the abstraction anyway since clang-repl requires extra handling:

CppInterOp/lib/Interpreter/Compatibility.h

Lines 342 to 345 in 392b754

	inline llvm::orc::LLJIT* getExecutionEngine(clang::Interpreter& I) {
	#if CLANG_VERSION_MAJOR >= 14
	auto* engine = &llvm::cantFail(I.getExecutionEngine());
	return const_cast<llvm::orc::LLJIT*>(engine);

Another motivation is also to keep the compat:: abstraction layer consistent, and perform operations defined under compat to compat::Interpreter