[PATCH] D53593: [GCOV] Flush counters before forking to avoid counting the execution before fork twice

[calixte via Phabricator via llvm-commits]

calixte created this revision.
calixte added reviewers: vsk, davidxl.
Herald added a subscriber: llvm-commits.

This is replacement for patch in https://reviews.llvm.org/D49460.
When we fork, the counters are duplicate as they're and so the values are finally wrong when writing gcda for parent and child.
So just before to fork, we flush the counters and so the parent and the child have new counters set to zero.


Repository:
  rL LLVM

https://reviews.llvm.org/D53593

Files:
  lib/Transforms/Instrumentation/GCOVProfiling.cpp


Index: lib/Transforms/Instrumentation/GCOVProfiling.cpp
===================================================================
--- lib/Transforms/Instrumentation/GCOVProfiling.cpp
+++ lib/Transforms/Instrumentation/GCOVProfiling.cpp
@@ -109,6 +109,8 @@
   insertCounterWriteout(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
   Function *insertFlush(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
 
+  void AddFlushBeforeFork();
+
   enum class GCovFileType { GCNO, GCDA };
   std::string mangleName(const DICompileUnit *CU, GCovFileType FileType);
 
@@ -468,6 +470,8 @@
   this->TLI = &TLI;
   Ctx = &M.getContext();
 
+  AddFlushBeforeFork();
+
   if (Options.EmitNotes) emitProfileNotes();
   if (Options.EmitData) return emitProfileArcs();
   return false;
@@ -524,6 +528,35 @@
 	return false;
 }
 
+void GCOVProfiler::AddFlushBeforeFork() {
+  SmallVector<Instruction *, 2> Forks;
+  for (auto &F : M->functions()) {
+    for (auto &BB : F) {
+      for (auto &I : BB) {
+        if (CallInst *CI = dyn_cast<CallInst>(&I)) {
+          if (Function *Callee = CI->getCalledFunction()) {
+            if (Callee->getName() == "fork") {
+              FunctionType *FT = Callee->getFunctionType();
+              if (FT->getReturnType()->isIntegerTy(32) &&
+                  FT->getNumParams() == 0) {
+                Forks.push_back(&I);
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+
+  for (auto I : Forks) {
+    IRBuilder<> Builder(I);
+    FunctionType *FTy = FunctionType::get(Builder.getVoidTy(), {}, false);
+    Constant *GCOVFlush = M->getOrInsertFunction("__gcov_flush", FTy);
+    Builder.CreateCall(GCOVFlush);
+    I->getParent()->splitBasicBlock(I);
+  }
+}
+
 void GCOVProfiler::emitProfileNotes() {
   NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu");
   if (!CU_Nodes) return;


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