[llvm] [llvm-profgen] Improve sample profile density (PR #92144)

[via llvm-commits]

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@@ -768,9 +748,89 @@ void ProfileGenerator::populateBoundarySamplesForAllFunctions(
   }
 }
 
+// Note taht ideally the size should be the number of function's instruction.
+// However, for probe-based profile, we don't have the accurate instruction
+// count for each probe, Instead, the probe sample is the samples count for the
+// block, which is equivelant to total_instruction_samples/num_instruction in
+// one block. Hence, we use the number of probe as a proxy for the function's
+// size.
+void ProfileGeneratorBase::calculateBodySamplesAndSize(
+    const FunctionSamples &FSamples, uint64_t &TotalBodySamples,
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WenleiHe wrote:

Ok, can you add a comment explaining why we need to accumulate the samples manually instead of using `getTotalSamples`? including the fact that `--update-total-samples` is off and the reasoning, difference between AutoFDO and CSSPGO. A comment would be very useful because after a while someone may look at this code be very tempted to refactor / simplify it with `getTotalSamples`.

https://github.com/llvm/llvm-project/pull/92144