[llvm] [llvm][ctx_profile] Add instrumentation lowering (PR #90821)

[Snehasish Kumar via llvm-commits]

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@@ -22,3 +32,298 @@ static cl::list<std::string> ContextRoots(
 bool PGOCtxProfLoweringPass::isContextualIRPGOEnabled() {
   return !ContextRoots.empty();
 }
+
+// the names of symbols we expect in compiler-rt. Using a namespace for
+// readability.
+namespace CompilerRtAPINames {
+static auto StartCtx = "__llvm_ctx_profile_start_context";
+static auto ReleaseCtx = "__llvm_ctx_profile_release_context";
+static auto GetCtx = "__llvm_ctx_profile_get_context";
+static auto ExpectedCalleeTLS = "__llvm_ctx_profile_expected_callee";
+static auto CallsiteTLS = "__llvm_ctx_profile_callsite";
+} // namespace CompilerRtAPINames
+
+namespace {
+// The lowering logic and state.
+class CtxInstrumentationLowerer final {
+  Module &M;
+  ModuleAnalysisManager &MAM;
+  Type *ContextNodeTy = nullptr;
+  Type *ContextRootTy = nullptr;
+
+  DenseMap<const Function *, Constant *> ContextRootMap;
+  Function *StartCtx = nullptr;
+  Function *GetCtx = nullptr;
+  Function *ReleaseCtx = nullptr;
+  GlobalVariable *ExpectedCalleeTLS = nullptr;
+  GlobalVariable *CallsiteInfoTLS = nullptr;
+
+public:
+  CtxInstrumentationLowerer(Module &M, ModuleAnalysisManager &MAM);
+  // return true if lowering happened (i.e. a change was made)
+  bool lowerFunction(Function &F);
+};
+
+std::pair<uint32_t, uint32_t> getNrCountersAndCallsites(const Function &F) {
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snehasish wrote:

Write a short comment to describe what this does? I think it "returns the value of the first InstrProfIncrementInst and first InstrProfCallsite". Can there be more than one of these each? Should we have handling and assertions for this?

https://github.com/llvm/llvm-project/pull/90821