[PGO] Ensure non-zero entry-count after populateCounters

[mofarrell]

With sampled instrumentation (#69535), profile counts may appear corrupt and fixFuncEntryCount may assert. In particular a function can have a 0 block count for its entry, while later blocks are non zero. This is only likely to happen for colder functions, so it is reasonable to take any action that does not crash. Here we simply bail from fixing the entry count.

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[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Michael O'Farrell (mofarrell)

Changes

With sampled instrumentation (#69535), profile counts may appear corrupt and fixFuncEntryCount may assert. In particular a function can have a 0 block count for its entry, while later blocks are non zero. This is only likely to happen for colder functions, so it is reasonable to take any action that does not crash. Here we simply bail from fixing the entry count.

---

Full diff: https://github.com/llvm/llvm-project/pull/112029.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp (+2-4)

diff --git a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
index e6e474ed376069..23d34016173165 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -1970,11 +1970,9 @@ static void fixFuncEntryCount(PGOUseFunc &Func, LoopInfo &LI,
                               BranchProbabilityInfo &NBPI) {
   Function &F = Func.getFunc();
   BlockFrequencyInfo NBFI(F, NBPI, LI);
-#ifndef NDEBUG
   auto BFIEntryCount = F.getEntryCount();
-  assert(BFIEntryCount && (BFIEntryCount->getCount() > 0) &&
-         "Invalid BFI Entrycount");
-#endif
+  if (!BFIEntryCount || BFIEntryCount->getCount() == 0)
+    return;
   auto SumCount = APFloat::getZero(APFloat::IEEEdouble());
   auto SumBFICount = APFloat::getZero(APFloat::IEEEdouble());
   for (auto &BBI : F) {

[llvmbot]

@llvm/pr-subscribers-pgo

Author: Michael O'Farrell (mofarrell)

Changes

With sampled instrumentation (#69535), profile counts may appear corrupt and fixFuncEntryCount may assert. In particular a function can have a 0 block count for its entry, while later blocks are non zero. This is only likely to happen for colder functions, so it is reasonable to take any action that does not crash. Here we simply bail from fixing the entry count.

---

Full diff: https://github.com/llvm/llvm-project/pull/112029.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp (+2-4)

diff --git a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
index e6e474ed376069..23d34016173165 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -1970,11 +1970,9 @@ static void fixFuncEntryCount(PGOUseFunc &Func, LoopInfo &LI,
                               BranchProbabilityInfo &NBPI) {
   Function &F = Func.getFunc();
   BlockFrequencyInfo NBFI(F, NBPI, LI);
-#ifndef NDEBUG
   auto BFIEntryCount = F.getEntryCount();
-  assert(BFIEntryCount && (BFIEntryCount->getCount() > 0) &&
-         "Invalid BFI Entrycount");
-#endif
+  if (!BFIEntryCount || BFIEntryCount->getCount() == 0)
+    return;
   auto SumCount = APFloat::getZero(APFloat::IEEEdouble());
   auto SumBFICount = APFloat::getZero(APFloat::IEEEdouble());
   for (auto &BBI : F) {

[MatzeB]

• Changes makes sense to me
• Please provide a test if possible

[WenleiHe]

Beyond the point fix here, I'm wondering if we want to consider profile inference to smooth the counts for sampled IRPGO just like HW sample PGO. @xur-llvm wdyt?

[mofarrell]

Changed the fix to guarantee the function entry count is non zero after populateCounters.

[WenleiHe]

lgtm, thanks.