[IR][TLI] Cache getLibFunc() result on Function (NFC) (#72867)

Cache the result of the TLI libfunc lookup in the Function object. This
only caches the actual lookup of the LibFunc in the TLI map, but not the
prototype validation, as that might differ between different TLI
instances.

This uses the existing mechanism for invalidating the intrinsic ID when
the function name changes. The libfunc will be invalidated in that case
as well.

I don't believe this increases the size of Function on 64bit (which
currently has a trailing `bool` member), and I don't think we would
particularly care if it did, as Functions are uncommon as Values go.

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index 49e0c1c..c3706dc 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -912,7 +912,8 @@ Intrinsic::ID Function::lookupIntrinsicID(StringRef Name) {
                                                      : Intrinsic::not_intrinsic;
 }
 
-void Function::recalculateIntrinsicID() {
+void Function::updateAfterNameChange() {
+  LibFuncCache = UnknownLibFunc;
   StringRef Name = getName();
   if (!Name.startswith("llvm.")) {
     HasLLVMReservedName = false;