[llvm] [SampleProfile] Fix bug where remapper returns empty string and crashing Sample Profile loader (PR #71479)

[William Junda Huang via llvm-commits]

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@@ -1630,7 +1630,7 @@ void SampleProfileLoader::promoteMergeNotInlinedContextSamples(
         // separate map so that it does not rehash the original profile.
         if (!OutlineFS)
           OutlineFS = &OutlineFunctionSamples[
-              FunctionSamples::getCanonicalFnName(Callee->getName())];
+              FunctionId(FunctionSamples::getCanonicalFnName(Callee->getName()))];
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huangjd wrote:

It is intentionally using FunctionId constructor here to avoid that assert, and any other potential situation where a function with empty name is passed in. Since the front end is relatively independent, so we are not making any assumption there. Accepting an empty string in profile matching will at worst degrade the profile's accuracy but still result in a correct binary, which is something we want to ensure here: If both the source code and the sample profile file are valid, the compiler should not exit abnormally.

Also there's an upcoming patch which will make this moot (https://github.com/huangjd/llvm-project/tree/md5phase3) I am still validating it. 

https://github.com/llvm/llvm-project/pull/71479