[llvm] 19ac753 - [PGO] Improve hash-mismatch warning message

[Rong Xu via llvm-commits]

Author: Rong Xu
Date: 2022-07-15T13:44:55-07:00
New Revision: 19ac75364fc9fb49158dd17cd56ae55b4b6fa726

URL: https://github.com/llvm/llvm-project/commit/19ac75364fc9fb49158dd17cd56ae55b4b6fa726
DIFF: https://github.com/llvm/llvm-project/commit/19ac75364fc9fb49158dd17cd56ae55b4b6fa726.diff

LOG: [PGO] Improve hash-mismatch warning message

This patch improves FDO hash-mismatch handling:
(1) filter out warnings to weak functions.
Weak functions definition will be overridden by a strong definition by linker.
The hash mismatch in profile use compilation is expected.
Make the profile hash mismatch warning under the existing option (default true).

(2) add an option to trace the hash of functions with the specific string.
Note that an empty string parameter will trace all functions.

Differential Revision: https://reviews.llvm.org/D129002

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 3a29cd70e42ee..751b4a413a58b 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -210,12 +210,11 @@ cl::opt<bool>
 // Command line option to enable/disable the warning about a hash mismatch in
 // the profile data for Comdat functions, which often turns out to be false
 // positive due to the pre-instrumentation inline.
-static cl::opt<bool>
-    NoPGOWarnMismatchComdat("no-pgo-warn-mismatch-comdat", cl::init(true),
-                            cl::Hidden,
-                            cl::desc("The option is used to turn on/off "
-                                     "warnings about hash mismatch for comdat "
-                                     "functions."));
+static cl::opt<bool> NoPGOWarnMismatchComdatWeak(
+    "no-pgo-warn-mismatch-comdat-weak", cl::init(true), cl::Hidden,
+    cl::desc("The option is used to turn on/off "
+             "warnings about hash mismatch for comdat "
+             "or weak functions."));
 
 // Command line option to enable/disable select instruction instrumentation.
 static cl::opt<bool>
@@ -287,6 +286,11 @@ static cl::opt<unsigned> PGOVerifyBFICutoff(
     cl::desc("Set the threshold for pgo-verify-bfi: skip the counts whose "
              "profile count value is below."));
 
+static cl::opt<std::string> PGOTraceFuncHash(
+    "pgo-trace-func-hash", cl::init("-"), cl::Hidden,
+    cl::value_desc("function name"),
+    cl::desc("Trace the hash of the function with this name."));
+
 namespace llvm {
 // Command line option to turn on CFG dot dump after profile annotation.
 // Defined in Analysis/BlockFrequencyInfo.cpp:  -pgo-view-counts
@@ -630,6 +634,10 @@ void FuncPGOInstrumentation<Edge, BBInfo>::computeCFGHash() {
                       << ", High32 CRC = " << JCH.getCRC());
   }
   LLVM_DEBUG(dbgs() << ", Hash = " << FunctionHash << "\n";);
+
+  if (PGOTraceFuncHash != "-" && F.getName().contains(PGOTraceFuncHash))
+    dbgs() << "Funcname=" << F.getName() << ", Hash=" << FunctionHash
+           << " in building " << F.getParent()->getSourceFileName() << "\n";
 }
 
 // Check if we can safely rename this Comdat function.
@@ -1233,10 +1241,11 @@ bool PGOUseFunc::readCounters(IndexedInstrProfReader *PGOReader, bool &AllZeros,
         IsCS ? NumOfCSPGOMismatch++ : NumOfPGOMismatch++;
         SkipWarning =
             NoPGOWarnMismatch ||
-            (NoPGOWarnMismatchComdat &&
-             (F.hasComdat() ||
+            (NoPGOWarnMismatchComdatWeak &&
+             (F.hasComdat() || F.getLinkage() == GlobalValue::WeakAnyLinkage ||
               F.getLinkage() == GlobalValue::AvailableExternallyLinkage));
-        LLVM_DEBUG(dbgs() << "hash mismatch (skip=" << SkipWarning << ")");
+        LLVM_DEBUG(dbgs() << "hash mismatch (hash= " << FuncInfo.FunctionHash
+                          << " skip=" << SkipWarning << ")");
         // Emit function metadata indicating PGO profile mismatch.
         annotateFunctionWithHashMismatch(F, M->getContext());
       }