From 2bbffdb6c89b3e37e86fcd3e252eeeaf25ca216f Mon Sep 17 00:00:00 2001
From: Arthur Cohen <arthur.cohen@embecosm.com>
Date: Wed, 10 Aug 2022 16:08:38 +0200
Subject: [PATCH] intrinsics: Add copy_nonoverlapping<T>

This intrinsic is similar to C's memcpy (or in our case, GCC's
__builtin_memcpy) with the order of arguments swapped and knowledge
about the type of the operands. So we can desugar the following calls:

`copy_nonoverlapping::<T>(src, dst, count)`

can be converted to

`__builtin_memcpy(dst, src, count * size_of::<T>())`
---
 gcc/rust/backend/rust-builtins.h           |  8 +++
 gcc/rust/backend/rust-compile-intrinsic.cc | 71 +++++++++++++++++++++-
 2 files changed, 78 insertions(+), 1 deletion(-)

diff --git a/gcc/rust/backend/rust-builtins.h b/gcc/rust/backend/rust-builtins.h
index 13c16d15723f..2bfa6c6cdf79 100644
--- a/gcc/rust/backend/rust-builtins.h
+++ b/gcc/rust/backend/rust-builtins.h
@@ -122,6 +122,14 @@ class BuiltinsContext
     define_builtin ("breakpoint", BUILT_IN_TRAP, "__builtin_trap", "breakpoint",
 		    build_function_type (void_type_node, void_list_node),
 		    builtin_const | builtin_noreturn);
+
+    define_builtin (
+      "memcpy", BUILT_IN_MEMCPY, "__builtin_memcpy", "memcpy",
+      build_function_type_list (build_pointer_type (void_type_node),
+				build_pointer_type (void_type_node),
+				build_pointer_type (void_type_node),
+				size_type_node, NULL_TREE),
+      0);
   }
 
   // Define a builtin function.  BCODE is the builtin function code
diff --git a/gcc/rust/backend/rust-compile-intrinsic.cc b/gcc/rust/backend/rust-compile-intrinsic.cc
index 67e38c3261c1..b51206d95e26 100644
--- a/gcc/rust/backend/rust-compile-intrinsic.cc
+++ b/gcc/rust/backend/rust-compile-intrinsic.cc
@@ -25,6 +25,7 @@
 #include "rust-location.h"
 #include "rust-tree.h"
 #include "tree-core.h"
+#include "print-tree.h"
 
 namespace Rust {
 namespace Compile {
@@ -37,6 +38,8 @@ static tree
 transmute_handler (Context *ctx, TyTy::FnType *fntype);
 static tree
 rotate_handler (Context *ctx, TyTy::FnType *fntype, tree_code op);
+static tree
+copy_nonoverlapping_handler (Context *ctx, TyTy::FnType *fntype);
 
 static inline tree
 rotate_left_handler (Context *ctx, TyTy::FnType *fntype)
@@ -55,7 +58,8 @@ static const std::map<std::string,
 			{"size_of", &sizeof_handler},
 			{"transmute", &transmute_handler},
 			{"rotate_left", &rotate_left_handler},
-			{"rotate_right", &rotate_right_handler}};
+			{"rotate_right", &rotate_right_handler},
+			{"copy_nonoverlapping", &copy_nonoverlapping_handler}};
 
 Intrinsics::Intrinsics (Context *ctx) : ctx (ctx) {}
 
@@ -184,7 +188,9 @@ finalize_intrinsic_block (Context *ctx, tree fndecl)
   tree bind_tree = ctx->pop_block ();
 
   gcc_assert (TREE_CODE (bind_tree) == BIND_EXPR);
+
   DECL_SAVED_TREE (fndecl) = bind_tree;
+
   ctx->push_function (fndecl);
 }
 
@@ -373,5 +379,68 @@ rotate_handler (Context *ctx, TyTy::FnType *fntype, tree_code op)
   return fndecl;
 }
 
+/**
+ * fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
+ */
+static tree
+copy_nonoverlapping_handler (Context *ctx, TyTy::FnType *fntype)
+{
+  rust_assert (fntype->get_params ().size () == 3);
+  rust_assert (fntype->get_num_substitutions () == 1);
+
+  tree lookup = NULL_TREE;
+  if (check_for_cached_intrinsic (ctx, fntype, &lookup))
+    return lookup;
+
+  auto fndecl = compile_intrinsic_function (ctx, fntype);
+
+  // setup the params
+  std::vector<Bvariable *> param_vars;
+  compile_fn_params (ctx, fntype, fndecl, &param_vars);
+
+  if (!ctx->get_backend ()->function_set_parameters (fndecl, param_vars))
+    return error_mark_node;
+
+  enter_intrinsic_block (ctx, fndecl);
+
+  // BUILTIN copy_nonoverlapping BODY BEGIN
+
+  auto src = ctx->get_backend ()->var_expression (param_vars[0], Location ());
+  auto dst = ctx->get_backend ()->var_expression (param_vars[1], Location ());
+  auto count = ctx->get_backend ()->var_expression (param_vars[2], Location ());
+
+  // We want to create the following statement
+  // memcpy(dst, src, size_of::<T>());
+  // so
+  // memcpy(dst, src, size_expr);
+
+  auto *resolved_ty = fntype->get_substs ().at (0).get_param_ty ()->resolve ();
+  auto param_type = TyTyResolveCompile::compile (ctx, resolved_ty);
+
+  tree size_expr
+    = build2 (MULT_EXPR, size_type_node, TYPE_SIZE_UNIT (param_type), count);
+
+  tree memcpy_raw;
+  BuiltinsContext::get ().lookup_simple_builtin ("memcpy", &memcpy_raw);
+  rust_assert (memcpy_raw);
+  auto memcpy
+    = build_fold_addr_expr_loc (Location ().gcc_location (), memcpy_raw);
+
+  auto copy_call
+    = ctx->get_backend ()->call_expression (memcpy, {dst, src, size_expr},
+					    nullptr, Location ());
+
+  ctx->add_statement (copy_call);
+
+  // BUILTIN copy_nonoverlapping BODY END
+
+  finalize_intrinsic_block (ctx, fndecl);
+
+  // `memcpy` always has side effects, it is far from a pure function
+  TREE_SIDE_EFFECTS (fndecl) = 1;
+
+  return fndecl;
+}
+
 } // namespace Compile
 } // namespace Rust