[clang] [CIR] Initial upstreaming of idiom recognizer pass (PR #172486)

[Bruno Cardoso Lopes via cfe-commits]

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@@ -27,6 +27,8 @@ std::unique_ptr<Pass> createHoistAllocasPass();
 std::unique_ptr<Pass> createLoweringPreparePass();
 std::unique_ptr<Pass> createLoweringPreparePass(clang::ASTContext *astCtx);
 std::unique_ptr<Pass> createGotoSolverPass();
+std::unique_ptr<Pass> createIdiomRecognizerPass();
+std::unique_ptr<Pass> createIdiomRecognizerPass(clang::ASTContext *astCtx);
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bcardosolopes wrote:

> this pass should still live on as a sort of testing platform for such exploration

@andykaylor can you clarify what testing platform suggestion means?

https://github.com/llvm/llvm-project/pull/172486