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

[Nikita Popov via llvm-commits]

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@@ -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()));
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nikic wrote:

Is this getPointerCast() needed? If so, I think it's missing test coverage.

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