[gcc r17-2247] gccrs: intrinsic: Add arith_offset

https://gcc.gnu.org/g:574afa290276ce7bd67e905613d7b77f066b4a87

commit r17-2247-g574afa290276ce7bd67e905613d7b77f066b4a87
Author: Enes Cevik <[email protected]>
Date:   Fri Jun 26 16:40:51 2026 +0300

    gccrs: intrinsic: Add arith_offset
    
    This patch implements the 'arith_offset' compiler intrinsic. It moves a
    pointer forward or backward by a given number of elements. It does not
    cause Undefined Behavior if the pointer goes out of bounds.
    
    gcc/rust/ChangeLog:
    
            * backend/rust-compile-intrinsic.cc (generic_intrinsics): Add
            arith_offset handler to map.
            * backend/rust-intrinsic-handlers.cc (arith_offset_handler): New
            function.
            * backend/rust-intrinsic-handlers.h (arith_offset_handler): New
            declaration.
            * typecheck/rust-hir-type-check-intrinsic.cc
            (IntrinsicChecker::intrinsic_rules): Add arith_offset rule.
            * util/rust-intrinsic-values.h (class Intrinsics): Add
            ARITH_OFFSET constexpr.
    
    gcc/testsuite/ChangeLog:
    
            * rust/execute/arith-offset.rs: New test.
    
    Signed-off-by: Enes Cevik <[email protected]>

Diff:
---
 gcc/rust/backend/rust-compile-intrinsic.cc         |  1 +
 gcc/rust/backend/rust-intrinsic-handlers.cc        | 39 ++++++++++++++++++++++
 gcc/rust/backend/rust-intrinsic-handlers.h         |  2 ++
 .../typecheck/rust-hir-type-check-intrinsic.cc     |  3 ++
 gcc/rust/util/rust-intrinsic-values.h              |  1 +
 gcc/testsuite/rust/execute/arith-offset.rs         | 23 +++++++++++++
 6 files changed, 69 insertions(+)

diff --git a/gcc/rust/backend/rust-compile-intrinsic.cc b/gcc/rust/backend/rust-compile-intrinsic.cc
index 51531de3c65e..e9407e051115 100644
--- a/gcc/rust/backend/rust-compile-intrinsic.cc
+++ b/gcc/rust/backend/rust-compile-intrinsic.cc
@@ -29,6 +29,7 @@ using IValue = Values::Intrinsics;
 
 static const std::map<std::string, handlers::HandlerBuilder> generic_intrinsics
   = {{IValue::OFFSET, handlers::offset},
+     {IValue::ARITH_OFFSET, handlers::arith_offset_handler},
      {IValue::WRITE_BYTES, handlers::write_bytes_handler},
      {IValue::SIZE_OF, handlers::sizeof_handler},
      {IValue::MIN_ALIGN_OF, handlers::min_align_of_handler},
diff --git a/gcc/rust/backend/rust-intrinsic-handlers.cc b/gcc/rust/backend/rust-intrinsic-handlers.cc
index 24f831ec7ae6..735529cc947a 100644
--- a/gcc/rust/backend/rust-intrinsic-handlers.cc
+++ b/gcc/rust/backend/rust-intrinsic-handlers.cc
@@ -1935,6 +1935,45 @@ write_bytes_handler (Context *ctx, TyTy::FnType *fntype, location_t)
   return fndecl;
 }
 
+/**
+ * pub fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;
+ */
+tree
+arith_offset_handler (Context *ctx, TyTy::FnType *fntype, location_t expr_locus)
+{
+  rust_assert (fntype->get_params ().size () == 2);
+
+  auto fndecl = compile_intrinsic_function (ctx, fntype);
+
+  auto locus = fntype->get_locus ();
+
+  std::vector<Bvariable *> param_vars;
+  compile_fn_params (ctx, fntype, fndecl, &param_vars);
+
+  auto &dst_param = param_vars.at (0);
+  auto &size_param = param_vars.at (1);
+  rust_assert (param_vars.size () == 2);
+  if (!Backend::function_set_parameters (fndecl, param_vars))
+    return error_mark_node;
+
+  enter_intrinsic_block (ctx, fndecl);
+
+  // BUILTIN arith_offset FN BODY BEGIN
+
+  tree dst = Backend::var_expression (dst_param, locus);
+  tree size = Backend::var_expression (size_param, locus);
+  tree pointer_offset_expr = pointer_offset_expression (dst, size, expr_locus);
+  auto return_statement
+    = Backend::return_statement (fndecl, pointer_offset_expr, locus);
+  ctx->add_statement (return_statement);
+
+  // BUILTIN arith_offset FN BODY END
+
+  finalize_intrinsic_block (ctx, fndecl);
+
+  return fndecl;
+}
+
 } // namespace handlers
 } // namespace Compile
 } // namespace Rust
diff --git a/gcc/rust/backend/rust-intrinsic-handlers.h b/gcc/rust/backend/rust-intrinsic-handlers.h
index c088f9ff4d85..1c81417b7024 100644
--- a/gcc/rust/backend/rust-intrinsic-handlers.h
+++ b/gcc/rust/backend/rust-intrinsic-handlers.h
@@ -98,6 +98,8 @@ tree sorry (Context *ctx, TyTy::FnType *fntype, location_t expr_locus);
 
 tree write_bytes_handler (Context *ctx, TyTy::FnType *fntype,
 			  location_t expr_locus);
+tree arith_offset_handler (Context *ctx, TyTy::FnType *fntype,
+			   location_t expr_locus);
 
 } // namespace handlers
 
diff --git a/gcc/rust/typecheck/rust-hir-type-check-intrinsic.cc b/gcc/rust/typecheck/rust-hir-type-check-intrinsic.cc
index af27a2ddb982..0011e3203d52 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-intrinsic.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-intrinsic.cc
@@ -301,6 +301,9 @@ const std::unordered_map<std::string, IntrinsicRules>
     // pub fn black_box<T>(mut dummy: T) -> T
     {IValue::BLACK_BOX, {1, {IRT::FirstGeneric}, IRT::FirstGeneric}},
 
+    // pub fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;
+    {IValue::ARITH_OFFSET,
+     {1, {IRT::ConstPtrFirstGeneric, IRT::Isize}, IRT::ConstPtrFirstGeneric}},
     // fn write_bytes<T>(dst: *mut T, val: u8, count: usize)
     {IValue::WRITE_BYTES,
      {1, {IRT::MutPtrFirstGeneric, IRT::U8, IRT::Usize}, IRT::Unit}},
diff --git a/gcc/rust/util/rust-intrinsic-values.h b/gcc/rust/util/rust-intrinsic-values.h
index 10c5c1eb2b00..d47e66ce6e9f 100644
--- a/gcc/rust/util/rust-intrinsic-values.h
+++ b/gcc/rust/util/rust-intrinsic-values.h
@@ -157,6 +157,7 @@ public:
   static constexpr auto &TYPE_NAME = "type_name";
   static constexpr auto &FORGET = "forget";
   static constexpr auto &BLACK_BOX = "black_box";
+  static constexpr auto &ARITH_OFFSET = "arith_offset";
   static constexpr auto &WRITE_BYTES = "write_bytes";
 };
 } // namespace Values
diff --git a/gcc/testsuite/rust/execute/arith-offset.rs b/gcc/testsuite/rust/execute/arith-offset.rs
new file mode 100644
index 000000000000..2daf1d7bed6d
--- /dev/null
+++ b/gcc/testsuite/rust/execute/arith-offset.rs
@@ -0,0 +1,23 @@
+#![feature(no_core, intrinsics, lang_items)]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}
+
+extern "rust-intrinsic" {
+    fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;
+}
+
+fn main() -> i32 {
+    let base_addr: usize = 0;
+    let ptr = base_addr as *const u64;
+
+    unsafe {
+        let wrap_ptr = arith_offset(ptr, -1);
+        if wrap_ptr as isize == -8_isize {
+            0 
+        } else {
+            1 
+        }
+    }
+}