Add a counter-function insertion pass

As discussed in https://reviews.llvm.org/D22666, our current mechanism to
support -pg profiling, where we insert calls to mcount(), or some similar
function, is fundamentally broken. We insert these calls in the frontend, which
means they get duplicated when inlining, and so the accumulated execution
counts for the inlined-into functions are wrong.

Because we don't want the presence of these functions to affect optimizaton,
they should be inserted in the backend. Here's a pass which would do just that.
The knowledge of the name of the counting function lives in the frontend, so
we're passing it here as a function attribute. Clang will be updated to use
this mechanism.

Differential Revision: https://reviews.llvm.org/D22825

llvm-svn: 280347

1 files changed, 62 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CountingFunctionInserter.cpp b/llvm/lib/CodeGen/CountingFunctionInserter.cpp
new file mode 100644
index 0000000..1e46a7a
--- /dev/null
+++ b/llvm/lib/CodeGen/CountingFunctionInserter.cpp
@@ -0,0 +1,62 @@
+//===- CountingFunctionInserter.cpp - Insert mcount-like function calls ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Insert calls to counter functions, such as mcount, intended to be called
+// once per function, at the beginning of each function.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Pass.h"
+using namespace llvm;
+
+namespace {
+  struct CountingFunctionInserter : public FunctionPass {
+    static char ID; // Pass identification, replacement for typeid
+    CountingFunctionInserter() : FunctionPass(ID) {
+      initializeCountingFunctionInserterPass(*PassRegistry::getPassRegistry());
+    }
+    
+    void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.addPreserved<GlobalsAAWrapperPass>();
+    }
+
+    bool runOnFunction(Function &F) override {
+      std::string CountingFunctionName =
+        F.getFnAttribute("counting-function").getValueAsString();
+      if (CountingFunctionName.empty())
+        return false;
+
+      Type *VoidTy = Type::getVoidTy(F.getContext());
+      Constant *CountingFn =
+        F.getParent()->getOrInsertFunction(CountingFunctionName,
+                                           VoidTy, nullptr);
+      CallInst::Create(CountingFn, "", &*F.begin()->getFirstInsertionPt());
+      return true;
+    }
+  };
+  
+  char CountingFunctionInserter::ID = 0;
+}
+
+INITIALIZE_PASS(CountingFunctionInserter, "cfinserter", 
+                "Inserts calls to mcount-like functions", false, false)
+
+//===----------------------------------------------------------------------===//
+//
+// CountingFunctionInserter - Give any unnamed non-void instructions "tmp" names.
+//
+FunctionPass *llvm::createCountingFunctionInserterPass() {
+  return new CountingFunctionInserter();
+}