llvm · fhahn · Dec 20, 2024
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
@@ -29153,6 +29153,45 @@ attach various forms of information to operands that dominate specific
 uses.  It is not meant for general use, only for building temporary
 renaming forms that require value splits at certain points.
 
+.. _int_dereferenceable:
+
+'``llvm.dereferenceable``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare void @llvm.dereferenceable(ptr %p, i64 <size>)
+
+Overview:
+"""""""""
+
+The ``llvm.dereferenceable`` allows the optimizer to assume that the returned
+pointer is dereferenceable at the point the intrinsic is called.
+
+Arguments:
+""""""""""
+
+The arguments of the call are the pointer which will be marked as
+dereferenceable and the number of bytes known to be dereferenceable. ``<size>``
+must be a constant.
+
+Semantics:
+""""""""""
+
+The intrinsic returns the input pointer. The returned pointer is dereferenceable
+at the point the intrinsic is called. A pointer that is dereferenceable can be
+loaded from speculatively without a risk of trapping. This implies that the
+input pointer is not null and neither undef or poison. The number of bytes known
+to be dereferenceable is provided as second argument. It is legal for the number
+of bytes to be less than the size of the pointee type.
+
+The semantics above match the semantics of the ``dereferenceable(<n>)``
+parameter attribute.
+
+
 .. _type.test:
 
 '``llvm.type.test``' Intrinsic

diff --git a/llvm/include/llvm/IR/Intrinsics.td b/llvm/include/llvm/IR/Intrinsics.td
@@ -954,6 +954,10 @@ def int_call_preallocated_teardown : DefaultAttrsIntrinsic<[], [llvm_token_ty]>;
 def int_callbr_landingpad : Intrinsic<[llvm_any_ty], [LLVMMatchType<0>],
                                       [IntrNoMerge]>;
 
+// Attach dereferenceability information to a pointer.
+def int_dereferenceable: DefaultAttrsIntrinsic<[llvm_ptr_ty], [llvm_ptr_ty, llvm_i64_ty],
+                             [IntrInaccessibleMemOnly, ImmArg<ArgIndex<1>>]>;
+
 //===------------------- Standard C Library Intrinsics --------------------===//
 //
 

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -8293,6 +8293,9 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
     visitVectorExtractLastActive(I, Intrinsic);
     return;
   }
+  case Intrinsic::dereferenceable:
+    setValue(&I, getValue(I.getArgOperand(0)));
+    return;
   }
 }
 

diff --git a/llvm/test/CodeGen/AArch64/dereferenceable-intrinsics.ll b/llvm/test/CodeGen/AArch64/dereferenceable-intrinsics.ll
@@ -0,0 +1,14 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=arm64-apple-macosx -o - %s | FileCheck %s
+
+declare ptr @llvm.dereferenceable(ptr, i64 immarg)
+
+define i64 @foo(ptr %a) {
+; CHECK-LABEL: foo:
+; CHECK:       ; %bb.0:
+; CHECK-NEXT:    ldr x0, [x0]
+; CHECK-NEXT:    ret
+  %d = call ptr @llvm.dereferenceable(ptr %a, i64 4)
+  %l = load i64, ptr %d
+  ret i64 %l
+}
diff --git a/llvm/test/Verifier/dereferenceable-intrinsics.ll b/llvm/test/Verifier/dereferenceable-intrinsics.ll
@@ -0,0 +1,11 @@
+; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s
+
+declare ptr @llvm.dereferenceable(ptr, i64 immarg)
+
+define void @transpose(ptr %p, i64 %x) {
+; CHECK: immarg operand has non-immediate parameter
+  %d.0 = call ptr @llvm.dereferenceable(ptr %p, i64 4)
+  %d.1 = call ptr @llvm.dereferenceable(ptr %p, i64 %x)
+  ret void
+}
+
-Original file line number
+Diff line change
@@ Expand Up @@
         visitVectorExtractLastActive(I, Intrinsic);
         return;
       }
+      case Intrinsic::dereferenceable:
+        setValue(&I, getValue(I.getArgOperand(0)));
+        return;
       }
     }
@@ Expand Down @@