[clang] [CIR] Update get_global type for rewritten callees (PR #214082)

[Andy Kaylor via cfe-commits]

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@@ -691,17 +691,35 @@ void CallConvLoweringPass::runOnOperation() {
     return;
   }
 
-  // Rewrite each function together with every direct call to it.  By the
-  // time we move on to function F+1, F's signature and every direct call to
-  // F have already been brought into alignment, and F+1..FN are still in
-  // their original (mutually consistent) form, so the IR is verifier-clean
-  // at every outer-iteration boundary.
+  // A cir.get_global holding a function's address carries the signature the
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andykaylor wrote:

This function has gotten quite large. At some point, we should revisit this and break it down into smaller functions with more focused purpose.

https://github.com/llvm/llvm-project/pull/214082