[clang] [compiler-rt] [llvm] [InstrProf] Single byte counters in coverage (PR #75425)

[Ellis Hoag via cfe-commits]

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@@ -821,15 +822,23 @@ void InstrProfRecord::merge(InstrProfRecord &Other, uint64_t Weight,
 
   for (size_t I = 0, E = Other.Counts.size(); I < E; ++I) {
     bool Overflowed;
-    uint64_t Value =
-        SaturatingMultiplyAdd(Other.Counts[I], Weight, Counts[I], &Overflowed);
-    if (Value > getInstrMaxCountValue()) {
-      Value = getInstrMaxCountValue();
-      Overflowed = true;
+    uint64_t Value;
+    // When a profile has single byte coverage, use || to merge counters.
+    if (HasSingleByteCoverage)
+      Value = Other.Counts[I] || Counts[I];
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ellishg wrote:

Yes, we actually do use block coverage to collect many raw profiles and aggregate them into an indexed profile. Since the counts can be larger than one, it helps differentiate between some hot and cold blocks during optimization.

https://github.com/llvm/llvm-project/pull/75425