[llvm-profdata] Change instr prof counter overflow to saturate rather than discard

Summary: This changes overflow handling during instrumentation profile merge. Rathar than throwing away records that would result in counter overflow, merged counts are instead clamped to the maximum representable value. A warning about counter overflow is still surfaced to the user as before.

Reviewers: dnovillo, davidxl, silvas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D14893

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254525 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 10 insertions, 7 deletions

diff --git a/include/llvm/ProfileData/InstrProf.h b/include/llvm/ProfileData/InstrProf.h
index 13f6c70b3e8..95648511910 100644
--- a/include/llvm/ProfileData/InstrProf.h
+++ b/include/llvm/ProfileData/InstrProf.h
@@ -428,19 +428,22 @@ instrprof_error InstrProfRecord::merge(InstrProfRecord &Other) {
   if (Counts.size() != Other.Counts.size())
     return instrprof_error::count_mismatch;
 
+  instrprof_error Result = instrprof_error::success;
+
   for (size_t I = 0, E = Other.Counts.size(); I < E; ++I) {
-    if (Counts[I] + Other.Counts[I] < Counts[I])
-      return instrprof_error::counter_overflow;
-    Counts[I] += Other.Counts[I];
+    bool ResultOverflowed;
+    Counts[I] = SaturatingAdd(Counts[I], Other.Counts[I], ResultOverflowed);
+    if (ResultOverflowed)
+      Result = instrprof_error::counter_overflow;
   }
 
   for (uint32_t Kind = IPVK_First; Kind <= IPVK_Last; ++Kind) {
-    instrprof_error result = mergeValueProfData(Kind, Other);
-    if (result != instrprof_error::success)
-      return result;
+    instrprof_error MergeValueResult = mergeValueProfData(Kind, Other);
+    if (MergeValueResult != instrprof_error::success)
+      Result = MergeValueResult;
   }
 
-  return instrprof_error::success;
+  return Result;
 }
 
 inline support::endianness getHostEndianness() {