[llvm] [InstCombine] Combine ptrauth constants into ptrauth intrinsics. (PR #94705)

[Ahmed Bougacha via llvm-commits]

================
@@ -2661,6 +2662,27 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
         AuthDisc = CI->getArgOperand(2);
       } else
         break;
+    } else if (auto *PtrToInt = dyn_cast<PtrToIntOperator>(Ptr)) {
+      // ptrauth constants are equivalent to a call to @llvm.ptrauth.sign for
+      // our purposes, so check for that too.
+      auto *CPA = dyn_cast<ConstantPtrAuth>(PtrToInt->getOperand(0));
+      if (!CPA || !CPA->isKnownCompatibleWith(Key, Disc, DL))
+        break;
+
+      // resign(ptrauth(p,ks,ds),ks,ds,kr,dr) -> ptrauth(p,kr,dr)
+      if (NeedSign && isa<ConstantInt>(II->getArgOperand(4))) {
+        auto *SignKey = cast<ConstantInt>(II->getArgOperand(3));
+        auto *SignDisc = cast<ConstantInt>(II->getArgOperand(4));
+        auto *SignAddrDisc = ConstantPointerNull::get(Builder.getPtrTy());
+        auto *NewCPA = ConstantPtrAuth::get(CPA->getPointer(), SignKey,
+                                            SignDisc, SignAddrDisc);
+        replaceInstUsesWith(
+            *II, ConstantExpr::getPointerCast(NewCPA, II->getType()));
----------------
ahmedbougacha wrote:

Heh I thought this was another remnant of typed pointers, but this one is indeed needed, to reconcile the i64-centric ptrauth intrinsics with ptrs in ptr contexts elsewhere, i.e. the `ptrtoint` in:
```
; CHECK-NEXT:    ret i64 ptrtoint (ptr ptrauth (ptr @foo, i32 0, i64 42) to i64)

  %tmp0 = ptrtoint ptr %p to i64
  %authed = call i64 @llvm.ptrauth.resign(i64 ptrtoint(ptr ptrauth(ptr @foo, i32 1, i64 1234) to i64), i32 1, i64 1234, i32 0, i64 42)
  ret i64 %authed
```

https://github.com/llvm/llvm-project/pull/94705