Fix PR 23499

[Diego Novillo]

Based on our IRC discussion, I think this will address the multiple
copy problem on ELF systems.  By placing the counters in the same
comdat section as its associated function, we get the linker to
discard them together with the discarded function.

I don't think we need to create another test case just to trigger this
bug.  A small modification to the existing test case exposes it. I can
create a new one, if you'd rather have a different test case for this,
though.

OK to commit?


Thanks.  Diego.
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diff --git a/lib/Transforms/Instrumentation/InstrProfiling.cpp b/lib/Transforms/Instrumentation/InstrProfiling.cpp
index 0718ddc..b12c475 100644
--- a/lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ b/lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -235,6 +235,12 @@ InstrProfiling::getOrCreateRegionCounters(InstrProfIncrementInst *Inc) {
   Data->setVisibility(Name->getVisibility());
   Data->setSection(getDataSection());
   Data->setAlignment(8);
+  // Place the data variable in the same comdat section as
+  // its parent function. Otherwise, we may get multiple
+  // counters for the same function in certain cases
+  // (https://llvm.org/bugs/show_bug.cgi?id=23499).
+  Function* F = Inc->getParent()->getParent();
+  Data->setComdat(F->getComdat());
 
   // Mark the data variable as used so that it isn't stripped out.
   UsedVars.push_back(Data);
diff --git a/test/profile/Inputs/instrprof-dynamic-header.h b/test/profile/Inputs/instrprof-dynamic-header.h
index 1dc2e37..4d4a513 100644
--- a/test/profile/Inputs/instrprof-dynamic-header.h
+++ b/test/profile/Inputs/instrprof-dynamic-header.h
@@ -1,5 +1,8 @@
+extern int X;
 template <class T> void bar() {
-  if (true) {}
+  if (X) {
+    X *= 4;
+  }
 }
 void a();
 void b();
diff --git a/test/profile/Inputs/instrprof-dynamic-main.cpp b/test/profile/Inputs/instrprof-dynamic-main.cpp
index 0dd6021..5ba46ad 100644
--- a/test/profile/Inputs/instrprof-dynamic-main.cpp
+++ b/test/profile/Inputs/instrprof-dynamic-main.cpp
@@ -1,7 +1,9 @@
 #include "instrprof-dynamic-header.h"
+int X = 0;
 void foo(int K) { if (K) {} }
 int main(int argc, char *argv[]) {
   foo(5);
+  X++;
   bar<void>();
   a();
   b();