[IR] Make intrinsic checks more efficient (NFC) (#148682)

Directly cast the callee operand instead of going through
getCalledFunction(). We can do this because for intrinsics the function
type between the call and the function is guaranteed to match.

This is a minor compile-time improvement as is, but has a much bigger
impact with a future change that makes getCalledFunction() more
expensive.

There is some code duplication between these four uses, but they are
each just different enough that representing one in terms of another
would be less efficient.

Author: nikic

llvm/include/llvm/IR/IntrinsicInst.h

@@ -54,7 +54,7 @@ class IntrinsicInst : public CallInst {
 
   /// Return the intrinsic ID of this intrinsic.
   Intrinsic::ID getIntrinsicID() const {
-    return getCalledFunction()->getIntrinsicID();
+    return cast<Function>(getCalledOperand())->getIntrinsicID();
   }
 
   bool isAssociative() const {
@@ -131,9 +131,8 @@ class IntrinsicInst : public CallInst {
 
   /// Methods for support type inquiry through isa, cast, and dyn_cast:
   static bool classof(const CallInst *I) {
-    if (const Function *CF = I->getCalledFunction())
-      return CF->isIntrinsic();
-    return false;
+    auto *F = dyn_cast_or_null<Function>(I->getCalledOperand());
+    return F && F->isIntrinsic();
   }
   static bool classof(const Value *V) {
     return isa<CallInst>(V) && classof(cast<CallInst>(V));

llvm/include/llvm/IR/PatternMatch.h

@@ -2633,7 +2633,7 @@ struct IntrinsicID_match {
 
   template <typename OpTy> bool match(OpTy *V) const {
     if (const auto *CI = dyn_cast<CallInst>(V))
-      if (const auto *F = CI->getCalledFunction())
+      if (const auto *F = dyn_cast_or_null<Function>(CI->getCalledOperand()))
         return F->getIntrinsicID() == ID;
     return false;
   }

llvm/lib/IR/Instructions.cpp

@@ -355,7 +355,7 @@ bool CallBase::isTailCall() const {
 }
 
 Intrinsic::ID CallBase::getIntrinsicID() const {
-  if (auto *F = getCalledFunction())
+  if (auto *F = dyn_cast_or_null<Function>(getCalledOperand()))
     return F->getIntrinsicID();
   return Intrinsic::not_intrinsic;
 }