[PATCH] D129002: [PGO] Improve hash-mismatch warning message

[Rong Xu via Phabricator via llvm-commits]

xur created this revision.
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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.


https://reviews.llvm.org/D129002

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


Index: llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -210,12 +210,11 @@
 // 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 @@
     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 @@
                       << ", 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 @@
         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());
       }


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