[MemProf] Disable hot hints by default

llvm/lib/Analysis/MemoryProfileInfo.cpp

@@ -42,6 +42,11 @@ cl::opt<unsigned> MemProfMinAveLifetimeAccessDensityHotThreshold(
     cl::desc("The minimum TotalLifetimeAccessDensity / AllocCount for an "
              "allocation to be considered hot"));
 
+cl::opt<bool>
+    MemProfUseHotHints("memprof-use-hot-hints", cl::init(false), cl::Hidden,
+                       cl::desc("Enable use of hot hints (only supported for "
+                                "unambigously hot allocations)"));
+
 cl::opt<bool> MemProfReportHintedSizes(
     "memprof-report-hinted-sizes", cl::init(false), cl::Hidden,
     cl::desc("Report total allocation sizes of hinted allocations"));
@@ -60,8 +65,9 @@ AllocationType llvm::memprof::getAllocType(uint64_t TotalLifetimeAccessDensity,
 
   // The access densities are multiplied by 100 to hold 2 decimal places of
   // precision, so need to divide by 100.
-  if (((float)TotalLifetimeAccessDensity) / AllocCount / 100 >
-      MemProfMinAveLifetimeAccessDensityHotThreshold)
+  if (MemProfUseHotHints &&
+      ((float)TotalLifetimeAccessDensity) / AllocCount / 100 >
+          MemProfMinAveLifetimeAccessDensityHotThreshold)
     return AllocationType::Hot;
 
   return AllocationType::NotCold;

llvm/test/Transforms/PGOProfile/memprof.ll

@@ -84,6 +84,8 @@
 ; RUN: llvm-profdata merge -memprof-random-hotness -memprof-random-hotness-seed=1730170724 %S/Inputs/memprof.memprofraw --profiled-binary %S/Inputs/memprof.exe -o %t.memprofdatarand2 2>&1 | FileCheck %s --check-prefix=RAND2
 ; RAND2: random hotness seed = 1730170724
 ; RUN: opt < %s -passes='memprof-use<profile-filename=%t.memprofdatarand2>' -pgo-warn-missing-function -S -stats 2>&1 | FileCheck %s --check-prefixes=MEMPROFRAND2,ALL,MEMPROFONLY,MEMPROFSTATS
+;; Check with hot hints enabled
+; RUN: opt < %s -memprof-use-hot-hints -passes='memprof-use<profile-filename=%t.memprofdatarand2>' -pgo-warn-missing-function -S -stats 2>&1 | FileCheck %s --check-prefixes=MEMPROFRAND2HOT
 
 ; MEMPROFMATCHINFO: MemProf notcold context with id 1093248920606587996 has total profiled size 10 is matched
 ; MEMPROFMATCHINFO: MemProf notcold context with id 5725971306423925017 has total profiled size 10 is matched
@@ -408,8 +410,15 @@ for.end:                                          ; preds = %for.cond
 ; MEMPROFRAND2: !"cold"
 ; MEMPROFRAND2: !"cold"
 ; MEMPROFRAND2: !"cold"
-; MEMPROFRAND2: !"hot"
-; MEMPROFRAND2: !"hot"
+; MEMPROFRAND2: !"notcold"
+; MEMPROFRAND2: !"notcold"
+
+;; With hot hints enabled the last 2 should be hot.
+; MEMPROFRAND2HOT: !"cold"
+; MEMPROFRAND2HOT: !"cold"
+; MEMPROFRAND2HOT: !"cold"
+; MEMPROFRAND2HOT: !"hot"
+; MEMPROFRAND2HOT: !"hot"
 
 ; MEMPROFSTATS:  8 memprof - Number of alloc contexts in memory profile.
 ; MEMPROFSTATS: 10 memprof - Number of callsites in memory profile.

llvm/test/Transforms/PGOProfile/memprof_loop_unroll.ll

@@ -10,7 +10,9 @@
 ;; $ clang++ -gmlt -fdebug-info-for-profiling -S %S/Inputs/memprof_loop_unroll_b.cc -emit-llvm
 
 ; RUN: llvm-profdata merge %S/Inputs/memprof_loop_unroll.memprofraw --profiled-binary %S/Inputs/memprof_loop_unroll.exe -o %t.memprofdata
-; RUN: opt < %s -passes='memprof-use<profile-filename=%t.memprofdata>' -S -memprof-report-hinted-sizes 2>&1 | FileCheck %s
+;; Set the minimum lifetime threshold to 0 to ensure that one context is
+;; considered cold (the other will be notcold).
+; RUN: opt < %s -passes='memprof-use<profile-filename=%t.memprofdata>' -S -memprof-report-hinted-sizes -memprof-ave-lifetime-cold-threshold=0 2>&1 | FileCheck %s
 
 ;; Conservatively annotate as not cold. We get two messages as there are two
 ;; unrolled copies of the allocation.

llvm/unittests/Analysis/MemoryProfileInfoTest.cpp

@@ -25,6 +25,7 @@ using namespace llvm::memprof;
 extern cl::opt<float> MemProfLifetimeAccessDensityColdThreshold;
 extern cl::opt<unsigned> MemProfAveLifetimeColdThreshold;
 extern cl::opt<unsigned> MemProfMinAveLifetimeAccessDensityHotThreshold;
+extern cl::opt<bool> MemProfUseHotHints;
 
 namespace {
 
@@ -81,14 +82,23 @@ TEST_F(MemoryProfileInfoTest, GetAllocType) {
   //    MemProfMinAveLifetimeAccessDensityHotThreshold
   // so compute the HotTotalLifetimeAccessDensityThreshold  at the threshold.
   const uint64_t HotTotalLifetimeAccessDensityThreshold =
-      (uint64_t)(MemProfMinAveLifetimeAccessDensityHotThreshold * AllocCount * 100);  
-
-
+      (uint64_t)(MemProfMinAveLifetimeAccessDensityHotThreshold * AllocCount *
+                 100);
+
+  // Make sure the option for detecting hot allocations is set.
+  MemProfUseHotHints = true;
   // Test Hot
   // More accesses per byte per sec than hot threshold is hot.
   EXPECT_EQ(getAllocType(HotTotalLifetimeAccessDensityThreshold + 1, AllocCount,
                          ColdTotalLifetimeThreshold + 1),
-            AllocationType::Hot);  
+            AllocationType::Hot);
+  // Undo the manual set of the option above.
+  cl::ResetAllOptionOccurrences();
+
+  // Without MemProfUseHotHints (default) we should treat simply as NotCold.
+  EXPECT_EQ(getAllocType(HotTotalLifetimeAccessDensityThreshold + 1, AllocCount,
+                         ColdTotalLifetimeThreshold + 1),
+            AllocationType::NotCold);
 
   // Test Cold
   // Long lived with less accesses per byte per sec than cold threshold is cold.