[llvm-branch-commits] [llvm] [llvm-profgen] Extend llvm-profgen to generate vtable profiles with data access events. (PR #148013)

[Mingming Liu via llvm-branch-commits]

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@@ -1027,6 +1027,20 @@ class FunctionSamples {
     return VirtualCallsiteTypeCounts[mapIRLocToProfileLoc(Loc)];
   }
 
+  /// At location \p Loc, add a type sample for the given \p Type with
+  /// \p Count. This function uses saturating arithmetic to clamp the result to
+  /// maximum uint64_t (the counter type) and returns counter_overflow to caller
+  /// if the actual result is larger than maximum uint64_t.
+  sampleprof_error addTypeSamplesAt(const LineLocation &Loc, FunctionId Type,
+                                    uint64_t Count) {
+    auto &TypeCounts = getTypeSamplesAt(Loc);
+    bool Overflowed = false;
+    TypeCounts[Type] = SaturatingMultiplyAdd(Count, /* Weight= */ (uint64_t)1,
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mingmingl-llvm wrote:

As clarified offline, the `SaturatingMultiplyAdd` will clamp the result if overflow happens, and we insert the return value of `SaturatingMultiplyAdd`. From this perspective, counter_overflow is more of informative warning as opposed to a real error that wraps around a large unsigned integer into another value. 

I updated the comment to make this more explicit, and will probably prepare a separate change around the warning handling (in SampleProf or InstrProf).

https://github.com/llvm/llvm-project/pull/148013