[clang] [clang-repl][CodeGen] Add setOptLevel, #pragma clang repl optimize(N) (PR #214793)

[Jonas Hahnfeld via cfe-commits]

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@@ -39,7 +39,7 @@ namespace {
     IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS; // Only used for debug info.
     const HeaderSearchOptions &HeaderSearchOpts; // Only used for debug info.
     const PreprocessorOptions &PreprocessorOpts; // Only used for debug info.
-    const CodeGenOptions &CodeGenOpts;
+    CodeGenOptions CodeGenOpts; // copied in so caller can modify
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hahnjo wrote:

Commit ddeab07ca63235f8d952e1171b56fdb0f2d761c9 changed this to a reference. I think it should be sufficient to just update the `CodeGenOptions` in the `CompilerInvocation`, without passing copies around everywhere.

https://github.com/llvm/llvm-project/pull/214793