intrinsics: Add wrapping_{add, sub, mul}

Since wrapping arithmetics are guaranteed in Rust, we turn on the -fwrapv and simply desugar wrapping_{add, sub, mul} to their non-checked inner operations. This is the only difference between a wrapping add and a regular addition: The regular addition will gain some checks for overflows, which are simply not used for the wrapping version.

1 files changed, 7 insertions, 1 deletions

diff --git a/gcc/rust/rust-lang.cc b/gcc/rust/rust-lang.cc
index 95c92f8..ed822cc 100644
--- a/gcc/rust/rust-lang.cc
+++ b/gcc/rust/rust-lang.cc
@@ -152,8 +152,14 @@ grs_langhook_option_lang_mask (void)
 
 /* Initialize the options structure. */
 static void
-grs_langhook_init_options_struct (struct gcc_options * /* opts */)
+grs_langhook_init_options_struct (struct gcc_options *opts)
 {
+  /* Operations are always wrapping in Rust, even on signed integer. This is
+   * useful for the low level wrapping_{add, sub, mul} intrinsics, not for
+   * regular arithmetic operations which are checked for overflow anyway using
+   * builtins */
+  opts->x_flag_wrapv = 1;
+
   // nothing yet - used by frontends to change specific options for the language
   Rust::Session::get_instance ().init_options ();
 }