[clang] [compiler-rt] [llvm] [TypeProf][InstrFDO]Implement more efficient comparison sequence for indirect-call-promotion with vtable profiles. (PR #81442)

[Teresa Johnson via cfe-commits]

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@@ -103,27 +112,226 @@ static cl::opt<bool>
     ICPDUMPAFTER("icp-dumpafter", cl::init(false), cl::Hidden,
                  cl::desc("Dump IR after transformation happens"));
 
+// Indirect call promotion pass will fall back to function-based comparison if
+// vtable-count / function-count is smaller than this threshold.
+static cl::opt<float> ICPVTablePercentageThreshold(
+    "icp-vtable-percentage-threshold", cl::init(0.99), cl::Hidden,
+    cl::desc("The percentage threshold of vtable-count / function-count for "
+             "cost-benefit analysis. "));
+
+// Although comparing vtables can save a vtable load, we may need to compare
+// vtable pointer with multiple vtable address points due to class inheritance.
+// Comparing with multiple vtables inserts additional instructions on hot code
+// path; and doing so for earlier candidate of one icall can affect later
+// function candidate in an undesired way. We allow multiple vtable comparison
+// for the last function candidate and use the option below to cap the number
+// of vtables.
+static cl::opt<int> ICPMaxNumVTableLastCandidate(
+    "icp-max-num-vtable-last-candidate", cl::init(1), cl::Hidden,
+    cl::desc("The maximum number of vtable for the last candidate."));
+
 namespace {
 
+// The key is a vtable global variable, and the value is a map.
+// In the inner map, the key represents address point offsets and the value is a
+// constant for this address point.
+using VTableAddressPointOffsetValMap =
+    SmallDenseMap<const GlobalVariable *, std::unordered_map<int, Constant *>>;
+
+// A struct to collect type information for a virtual call site.
+struct VirtualCallSiteInfo {
+  // The offset from the address point to virtual function in the vtable.
+  uint64_t FunctionOffset;
+  // The instruction that computes the address point of vtable.
+  Instruction *VPtr;
+  // The compatible type used in LLVM type intrinsics.
+  StringRef CompatibleTypeStr;
+};
+
+// The key is a virtual call, and value is its type information.
+using VirtualCallSiteTypeInfoMap =
+    SmallDenseMap<const CallBase *, VirtualCallSiteInfo>;
+
+// The key is vtable GUID, and value is its value profile count.
+using VTableGUIDCountsMap = SmallDenseMap<uint64_t, uint64_t, 16>;
+
+// Returns the address point offset of the given compatible type.
+//
+// Type metadata of a vtable specifies the types that can container a pointer to
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teresajohnson wrote:

s/container/contain/

https://github.com/llvm/llvm-project/pull/81442