[gcc r17-2257] gccrs: turn on can_alias_all on build_pointer_type

https://gcc.gnu.org/g:de7fc69d08a863b526440bb94d7aa2697a5d7627

commit r17-2257-gde7fc69d08a863b526440bb94d7aa2697a5d7627
Author: Philip Herron <[email protected]>
Date:   Mon Jun 29 19:59:25 2026 +0100

    gccrs: turn on can_alias_all on build_pointer_type
    
    Rust semantics are that all raw pointers can alias but then we get stronger
    garentees on reference types.
    
    Fixes Rust-GCC#4536
    
    gcc/rust/ChangeLog:
    
            * rust-gcc.cc (pointer_type): turn on can alias
    
    gcc/testsuite/ChangeLog:
    
            * rust/execute/raw-pointer-aliasing.rs: New test.
    
    Signed-off-by: Philip Herron <[email protected]>

Diff:
---
 gcc/rust/rust-gcc.cc                               |  2 +-
 gcc/testsuite/rust/execute/raw-pointer-aliasing.rs | 25 ++++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/gcc/rust/rust-gcc.cc b/gcc/rust/rust-gcc.cc
index ab02bcd556a0..00f35638144e 100644
--- a/gcc/rust/rust-gcc.cc
+++ b/gcc/rust/rust-gcc.cc
@@ -444,7 +444,7 @@ pointer_type (tree to_type)
 {
   if (error_operand_p (to_type))
     return error_mark_node;
-  tree type = build_pointer_type (to_type);
+  tree type = build_pointer_type_for_mode (to_type, VOIDmode, true);
   return type;
 }
 
diff --git a/gcc/testsuite/rust/execute/raw-pointer-aliasing.rs b/gcc/testsuite/rust/execute/raw-pointer-aliasing.rs
new file mode 100644
index 000000000000..d19730b043fb
--- /dev/null
+++ b/gcc/testsuite/rust/execute/raw-pointer-aliasing.rs
@@ -0,0 +1,25 @@
+// { dg-options "-O2" }
+
+#![feature(no_core)]
+#![no_core]
+
+extern "C" {
+    fn malloc(n: u64) -> *mut u8;
+}
+
+fn f() -> i32 {
+    unsafe {
+        let p = malloc(4) as *mut i32;
+        *p = 27;
+        *(p as *mut i16) = 42;
+        *p
+    }
+}
+
+fn main() -> i32 {
+    if f() == 27 {
+        1
+    } else {
+        0
+    }
+}