[llvm] [BasicBlockSections] Always keep the entry block in the beginning of the function. (PR #74696)

[Sriraman Tallam via llvm-commits]

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@@ -213,10 +213,6 @@ Error BasicBlockSectionsProfileReader::ReadV1Profile() {
               Twine("duplicate basic block id found '") + BasicBlockIDStr +
               "'");
 
-        if (!BasicBlockID->BaseID && CurrentPosition)
-          return createProfileParseError(
-              "entry BB (0) does not begin a cluster.");
-
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tmsri wrote:

I see, so you are removing the error when "0" does not begin a cluster and forcing the entry block to be the beginning without any message.  I am fine with this change but we should add a note somewhere about this enforcement.  

https://github.com/llvm/llvm-project/pull/74696