[llvm] Insert symbols for prefetch targets read from basic blocks section profile. (PR #168439)

[Sriraman Tallam via llvm-commits]

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@@ -229,6 +229,13 @@ class MachineBasicBlock
   /// is only computed once and is cached.
   mutable MCSymbol *CachedMCSymbol = nullptr;
 
+  /// Contains the subblock indices in this block that are targets of code
+  /// prefetching. The subblock indexed `i` specifies that region after the
+  /// `i`th call (or the beginning of the block if `i==0`) to before the`i+1`th
+  /// callsite (or the end of the block). The prefetch target is always the
+  /// beginning of the subblock.
+  SmallVector<unsigned> PrefetchTargetSubblockIndexes;
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tmsri wrote:

define CallSiteIndex or SubblockIndex as unsigned type and use that instead of unsigned?

https://github.com/llvm/llvm-project/pull/168439