[llvm] 6fdc6f6 - [PGO][InstrProf] Do not promote count if the exit blocks contains ret instruction

[Rong Xu via llvm-commits]

Author: Rong Xu
Date: 2020-07-24T17:13:58-07:00
New Revision: 6fdc6f6c7d34af60c45c405f448370a684ef6f2a

URL: https://github.com/llvm/llvm-project/commit/6fdc6f6c7d34af60c45c405f448370a684ef6f2a
DIFF: https://github.com/llvm/llvm-project/commit/6fdc6f6c7d34af60c45c405f448370a684ef6f2a.diff

LOG: [PGO][InstrProf] Do not promote count if the exit blocks contains ret instruction

Skip profile count promotion if any of the ExitBlocks contains a ret
instruction. This is to prevent dumping of incomplete profile -- if the
the loop is a long running loop and dump is called in the middle
of the loop, the result profile is incomplete.

ExitBlocks containing a ret instruction is an indication of a long running
loop -- early exit to error handling code.

Differential Revision: https://reviews.llvm.org/D84379

Added: 
    

Modified: 
    llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
index 67bf264e8eea..c4a43abaa53c 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -1131,11 +1131,18 @@ bool PGOUseFunc::setInstrumentedCounts(
   if (NumCounters != CountFromProfile.size()) {
     return false;
   }
+  auto *FuncEntry = &*F.begin();
+
   // Set the profile count to the Instrumented BBs.
   uint32_t I = 0;
   for (BasicBlock *InstrBB : InstrumentBBs) {
     uint64_t CountValue = CountFromProfile[I++];
     UseBBInfo &Info = getBBInfo(InstrBB);
+    // If we reach here, we know that we have some nonzero count
+    // values in this function. The entry count should not be 0.
+    // Fix it if necessary.
+    if (InstrBB == FuncEntry && CountValue == 0)
+      CountValue = 1;
     Info.setBBInfoCount(CountValue);
   }
   ProfileCountSize = CountFromProfile.size();
@@ -1326,7 +1333,6 @@ void PGOUseFunc::populateCounters() {
   }
 #endif
   uint64_t FuncEntryCount = getBBInfo(&*F.begin()).CountValue;
-  F.setEntryCount(ProfileCount(FuncEntryCount, Function::PCT_Real));
   uint64_t FuncMaxCount = FuncEntryCount;
   for (auto &BB : F) {
     auto BI = findBBInfo(&BB);
@@ -1334,6 +1340,11 @@ void PGOUseFunc::populateCounters() {
       continue;
     FuncMaxCount = std::max(FuncMaxCount, BI->CountValue);
   }
+
+  // Fix the obviously inconsistent entry count.
+  if (FuncMaxCount > 0 && FuncEntryCount == 0)
+    FuncEntryCount = 1;
+  F.setEntryCount(ProfileCount(FuncEntryCount, Function::PCT_Real));
   markFunctionAttributes(FuncEntryCount, FuncMaxCount);
 
   // Now annotate select instructions