Add compatibility with LLVM 20.1

[svenstaro]

Description

This adds LLVM 20 compatibility. The changes are thankfully quite concise. Fixes #1963.

Tests

Checklist:

• I have read the contribution guidelines.
• I have updated the documentation, if applicable.
• I have ensured that the change is tested somewhere in the testsuite (adding new test cases if necessary).
• My code follows the prevailing code style of this project. If I haven't
  already run clang-format v17 before submitting, I definitely will look at
  the CI test that runs clang-format and fix anything that it highlights as
  being nonconforming.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: svenstaro / name: Sven-Hendrik Haase (c53e766)
• ✅ login: lgritz / name: Larry Gritz (07d53bc)

[lgritz]

Is that really all it takes to get fully LLVM 20 enabled? How did you test it?

I tried your patch on my end using the llvm 20 from Homebrew, and I'm still getting errors like

/Users/lg/code/osl/osl.lg/src/liboslexec/llvm_util.cpp:3659:53: error: 'getDeclaration' is deprecated: Use getOrInsertDeclaration instead [-Werror,-Wdeprecated-declarations]
            llvm::Function* func = llvm::Intrinsic::getDeclaration(
                                                    ^~~~~~~~~~~~~~
                                                    getOrInsertDeclaration

[robertkirkman]

Thank you, this patch does work for me on Termux (a subset of Android 7.0), but I do also see the warning mentioned by lgritz.

/data/data/com.termux/files/home/.termux-build/openshadinglanguage/src/src/liboslexec/llvm_util.cpp:3659:53: warning: 'getDeclaration' is deprecated: Use getOrInsertDeclaration instead [-Wdeprecated-declarations]
 3659 |             llvm::Function* func = llvm::Intrinsic::getDeclaration(
      |                                                     ^~~~~~~~~~~~~~
      |                                                     getOrInsertDeclaration
/data/data/com.termux/files/usr/include/llvm/IR/Intrinsics.h:100:3: note: 'getDeclaration' has been explicitly marked deprecated here
  100 |   LLVM_DEPRECATED("Use getOrInsertDeclaration instead",
      |   ^
/data/data/com.termux/files/usr/include/llvm/Support/Compiler.h:234:50: note: expanded from macro 'LLVM_DEPRECATED'
  234 | #define LLVM_DEPRECATED(MSG, FIX) __attribute__((deprecated(MSG, FIX)))
      |                                                  ^

It might be just luck, or subtle variations between LLVM platforms, that applying this patch allows the build to complete for some people but not others, because, even though svenstaro might be using -DSTOP_ON_WARNING=OFF (observed here), in my case -DSTOP_ON_WARNING=OFF does not seem necessary to build successfully. It is possible that additional changes might be necessary before all LLVM platforms, including Homebrew/MacOS, are supported by this PR.

[svenstaro]

Is that really all it takes to get fully LLVM 20 enabled? How did you test it?

I built and used blender against it.

I tried your patch on my end using the llvm 20 from Homebrew, and I'm still getting errors like

/Users/lg/code/osl/osl.lg/src/liboslexec/llvm_util.cpp:3659:53: error: 'getDeclaration' is deprecated: Use getOrInsertDeclaration instead [-Werror,-Wdeprecated-declarations]
            llvm::Function* func = llvm::Intrinsic::getDeclaration(
                                                    ^~~~~~~~~~~~~~
                                                    getOrInsertDeclaration

You can try to build without -Werror. I didn't fix all the deprecation warnings as I wasn't sure that effect it would have on other LLVM versions. I wanted to keep my patch minimal.

[lgritz]

I believe I have a fix. @svenstaro do you mind if I push an update to your fork to complete this PR?

[svenstaro]

Please go right ahead.

[lgritz]

With the additional changes I just made, it all seems to build and work properly when tested on my Mac with llvm20 from Homebrew.

[lgritz]

@svenstaro Please let me know if the changes I pushed look ok to you. We don't like to push to somebody else's PR and then merge it with their name attached if we aren't sure that they fully agree with the changes.