[gcc r14-8015] gccrs: Add intrinsics::assume

[gcc r14-8015] gccrs: Add intrinsics::assume

[Arthur Cohen]

https://gcc.gnu.org/g:b786f697dd3512db393c6517b1e7d1afe097aae1

commit r14-8015-gb786f697dd3512db393c6517b1e7d1afe097aae1
Author: Owen Avery <powerboat9.gamer@gmail.com>
Date:   Wed Sep 13 12:32:33 2023 -0400

    gccrs: Add intrinsics::assume
    
    gcc/rust/ChangeLog:
    
            * backend/rust-compile-intrinsic.cc
            (get_identifier): Add declaration.
            (assume_handler): New.
            (generic_intrinsics): Add assume_handler entry.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/assume.rs: New test.
    
    Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>

Diff:
---
 gcc/rust/backend/rust-compile-intrinsic.cc | 53 ++++++++++++++++++++++++++++++
 gcc/testsuite/rust/compile/assume.rs       | 13 ++++++++
 2 files changed, 66 insertions(+)

diff --git a/gcc/rust/backend/rust-compile-intrinsic.cc b/gcc/rust/backend/rust-compile-intrinsic.cc
index 420ed2dffe0..2433b989946 100644
--- a/gcc/rust/backend/rust-compile-intrinsic.cc
+++ b/gcc/rust/backend/rust-compile-intrinsic.cc
@@ -32,6 +32,11 @@
 
 #include "print-tree.h"
 
+// declaration taken from "stringpool.h"
+// the get_identifier macro causes compilation issues
+extern tree
+get_identifier (const char *);
+
 namespace Rust {
 namespace Compile {
 
@@ -83,6 +88,8 @@ static tree
 uninit_handler (Context *ctx, TyTy::FnType *fntype);
 static tree
 move_val_init_handler (Context *ctx, TyTy::FnType *fntype);
+static tree
+assume_handler (Context *ctx, TyTy::FnType *fntype);
 
 enum class Prefetch
 {
@@ -231,6 +238,7 @@ static const std::map<std::string,
     {"move_val_init", move_val_init_handler},
     {"likely", expect_handler (true)},
     {"unlikely", expect_handler (false)},
+    {"assume", assume_handler},
 };
 
 Intrinsics::Intrinsics (Context *ctx) : ctx (ctx) {}
@@ -1174,5 +1182,50 @@ expect_handler_inner (Context *ctx, TyTy::FnType *fntype, bool likely)
   return fndecl;
 }
 
+static tree
+assume_handler (Context *ctx, TyTy::FnType *fntype)
+{
+  // TODO: make sure this is actually helping the compiler optimize
+
+  rust_assert (fntype->get_params ().size () == 1);
+  rust_assert (fntype->param_at (0).second->get_kind ()
+	       == TyTy::TypeKind::BOOL);
+
+  tree lookup = NULL_TREE;
+  if (check_for_cached_intrinsic (ctx, fntype, &lookup))
+    return lookup;
+
+  auto fndecl = compile_intrinsic_function (ctx, fntype);
+
+  // TODO: make sure these are necessary
+  TREE_READONLY (fndecl) = 0;
+  DECL_DISREGARD_INLINE_LIMITS (fndecl) = 1;
+  DECL_ATTRIBUTES (fndecl) = tree_cons (get_identifier ("always_inline"),
+					NULL_TREE, DECL_ATTRIBUTES (fndecl));
+
+  std::vector<Bvariable *> param_vars;
+  compile_fn_params (ctx, fntype, fndecl, &param_vars);
+
+  if (!Backend::function_set_parameters (fndecl, param_vars))
+    return error_mark_node;
+
+  enter_intrinsic_block (ctx, fndecl);
+
+  // BUILTIN assume FN BODY BEGIN
+
+  tree val = Backend::var_expression (param_vars[0], UNDEF_LOCATION);
+
+  tree assume_expr = build_call_expr_internal_loc (UNDEF_LOCATION, IFN_ASSUME,
+						   void_type_node, 1, val);
+  TREE_SIDE_EFFECTS (assume_expr) = 1;
+
+  ctx->add_statement (assume_expr);
+  // BUILTIN size_of FN BODY END
+
+  finalize_intrinsic_block (ctx, fndecl);
+
+  return fndecl;
+}
+
 } // namespace Compile
 } // namespace Rust
diff --git a/gcc/testsuite/rust/compile/assume.rs b/gcc/testsuite/rust/compile/assume.rs
new file mode 100644
index 00000000000..4dc2fefa86a
--- /dev/null
+++ b/gcc/testsuite/rust/compile/assume.rs
@@ -0,0 +1,13 @@
+mod intrinsics {
+    extern "rust-intrinsic" {
+        pub fn assume(value: bool);
+    }
+}
+
+pub fn foo(v: i32) -> i32 {
+    unsafe { intrinsics::assume (v == 12); }
+    v
+}
+
+pub fn main() {
+}