Merge #1268

1268: Fix Slice Type Layout r=philberty a=philberty

Slices in Rust are represented by TypePaths such as '[i32]'. Though if you
actually try to use this explicit type-path you will hit errors such as
this type has an unknown size at compile time. This is because this is
actually what Rust calls a dynamically sized type. This means when you use
types such as: '&[i32]' it is not actually a reference type to a slice. Its
a slice in its entirety this means for lack of a better word when you use
'*const [i32]' or '&mut [i32]' we end up actually passing around a struct
by value _not_ at pointer/reference to it.

This patch changes the type-layout so that we handle this layout change
properly. This patch will also need to be applied to str types which I
believe have a similar layout for safety.

The patch also sets up TYPE_MAIN_VARIANT so that we can avoid unnessecary
view_convert_expressions between *const [i32] and &mut [i32] which will
have the same layout.

Reference:

https://doc.rust-lang.org/reference/dynamically-sized-types.html

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=672adac002939a2dab43b8d231adc1dc

Fixes #1232


Co-authored-by: Philip Herron <philip.herron@embecosm.com>

6 files changed, 156 insertions, 27 deletions

diff --git a/gcc/rust/backend/rust-compile-context.h b/gcc/rust/backend/rust-compile-context.h
index 8378554..096b65f 100644
--- a/gcc/rust/backend/rust-compile-context.h
+++ b/gcc/rust/backend/rust-compile-context.h
@@ -67,6 +67,17 @@ public:
     return type;
   }
 
+  tree insert_main_variant (tree type)
+  {
+    hashval_t h = type_hasher (type);
+    auto it = main_variants.find (h);
+    if (it != main_variants.end ())
+      return it->second;
+
+    main_variants.insert ({h, type});
+    return type;
+  }
+
   ::Backend *get_backend () { return backend; }
   Resolver::Resolver *get_resolver () { return resolver; }
   Resolver::TypeCheckContext *get_tyctx () { return tyctx; }
@@ -314,6 +325,7 @@ private:
   std::map<DefId, std::vector<std::pair<const TyTy::BaseType *, tree>>>
     mono_fns;
   std::map<HirId, tree> implicit_pattern_bindings;
+  std::map<hashval_t, tree> main_variants;
 
   // To GCC middle-end
   std::vector<tree> type_decls;
diff --git a/gcc/rust/backend/rust-compile-expr.cc b/gcc/rust/backend/rust-compile-expr.cc
index 824d6d3..b176ed2 100644
--- a/gcc/rust/backend/rust-compile-expr.cc
+++ b/gcc/rust/backend/rust-compile-expr.cc
@@ -123,6 +123,11 @@ void
 CompileExpr::visit (HIR::BorrowExpr &expr)
 {
   tree main_expr = CompileExpr::Compile (expr.get_expr ().get (), ctx);
+  if (SLICE_TYPE_P (TREE_TYPE (main_expr)))
+    {
+      translated = main_expr;
+      return;
+    }
 
   TyTy::BaseType *tyty = nullptr;
   if (!ctx->get_tyctx ()->lookup_type (expr.get_mappings ().get_hirid (),
@@ -164,6 +169,12 @@ CompileExpr::visit (HIR::DereferenceExpr &expr)
     }
 
   tree expected_type = TyTyResolveCompile::compile (ctx, tyty);
+  if (SLICE_TYPE_P (TREE_TYPE (main_expr)) && SLICE_TYPE_P (expected_type))
+    {
+      translated = main_expr;
+      return;
+    }
+
   bool known_valid = true;
   translated
     = ctx->get_backend ()->indirect_expression (expected_type, main_expr,
@@ -1092,6 +1103,32 @@ CompileExpr::type_cast_expression (tree type_to_cast_to, tree expr_tree,
       return fold_build1_loc (location.gcc_location (), VIEW_CONVERT_EXPR,
 			      type_to_cast_to, expr_tree);
     }
+  else if (TREE_CODE (type_to_cast_to) == POINTER_TYPE
+	   && SLICE_TYPE_P (TREE_TYPE (expr_tree)))
+    {
+      // returning a raw cast using NOP_EXPR seems to resut in an ICE:
+      //
+      // Analyzing compilation unit
+      // Performing interprocedural optimizations
+      //  <*free_lang_data> {heap 2644k} <visibility> {heap 2644k}
+      //  <build_ssa_passes> {heap 2644k} <opt_local_passes> {heap 2644k}during
+      //  GIMPLE pass: cddce
+      // In function ‘*T::as_ptr<i32>’:
+      // rust1: internal compiler error: in propagate_necessity, at
+      // tree-ssa-dce.cc:984 0x1d5b43e propagate_necessity
+      //         ../../gccrs/gcc/tree-ssa-dce.cc:984
+      // 0x1d5e180 perform_tree_ssa_dce
+      //         ../../gccrs/gcc/tree-ssa-dce.cc:1876
+      // 0x1d5e2c8 tree_ssa_cd_dce
+      //         ../../gccrs/gcc/tree-ssa-dce.cc:1920
+      // 0x1d5e49a execute
+      //         ../../gccrs/gcc/tree-ssa-dce.cc:1992
+
+      // this is returning the direct raw pointer of the slice an assumes a very
+      // specific layout
+      return ctx->get_backend ()->struct_field_expression (expr_tree, 0,
+							   location);
+    }
 
   return fold_convert_loc (location.gcc_location (), type_to_cast_to,
 			   expr_tree);
@@ -1261,9 +1298,13 @@ HIRCompileBase::resolve_adjustements (
 
 	case Resolver::Adjustment::AdjustmentType::IMM_REF:
 	  case Resolver::Adjustment::AdjustmentType::MUT_REF: {
-	    tree ptrtype
-	      = TyTyResolveCompile::compile (ctx, adjustment.get_expected ());
-	    e = address_expression (e, ptrtype, locus);
+	    if (!SLICE_TYPE_P (TREE_TYPE (e)))
+	      {
+		tree ptrtype
+		  = TyTyResolveCompile::compile (ctx,
+						 adjustment.get_expected ());
+		e = address_expression (e, ptrtype, locus);
+	      }
 	  }
 	  break;
 
@@ -1619,6 +1660,15 @@ CompileExpr::visit (HIR::ArrayIndexExpr &expr)
 				     index, expr.get_array_expr (),
 				     expr.get_index_expr ());
 
+      tree actual_type = TREE_TYPE (operator_overload_call);
+      bool can_indirect = TYPE_PTR_P (actual_type) || TYPE_REF_P (actual_type);
+      if (!can_indirect)
+	{
+	  // nothing to do
+	  translated = operator_overload_call;
+	  return;
+	}
+
       // lookup the expected type for this expression
       TyTy::BaseType *tyty = nullptr;
       bool ok
diff --git a/gcc/rust/backend/rust-compile-type.cc b/gcc/rust/backend/rust-compile-type.cc
index 102bc0a..707b2af 100644
--- a/gcc/rust/backend/rust-compile-type.cc
+++ b/gcc/rust/backend/rust-compile-type.cc
@@ -25,6 +25,13 @@
 namespace Rust {
 namespace Compile {
 
+static const std::string RUST_ENUM_DISR_FIELD_NAME = "RUST$ENUM$DISR";
+
+TyTyResolveCompile::TyTyResolveCompile (Context *ctx, bool trait_object_mode)
+  : ctx (ctx), trait_object_mode (trait_object_mode),
+    translated (error_mark_node), recurisve_ops (0)
+{}
+
 tree
 TyTyResolveCompile::compile (Context *ctx, const TyTy::BaseType *ty,
 			     bool trait_object_mode)
@@ -42,8 +49,6 @@ TyTyResolveCompile::compile (Context *ctx, const TyTy::BaseType *ty,
   return compiler.translated;
 }
 
-static const std::string RUST_ENUM_DISR_FIELD_NAME = "RUST$ENUM$DISR";
-
 // see: gcc/c/c-decl.cc:8230-8241
 // https://github.com/Rust-GCC/gccrs/blob/0024bc2f028369b871a65ceb11b2fddfb0f9c3aa/gcc/c/c-decl.c#L8229-L8241
 tree
@@ -375,24 +380,7 @@ TyTyResolveCompile::visit (const TyTy::ArrayType &type)
 void
 TyTyResolveCompile::visit (const TyTy::SliceType &type)
 {
-  std::vector<Backend::typed_identifier> fields;
-
-  tree element_type
-    = TyTyResolveCompile::compile (ctx, type.get_element_type ());
-  tree data_field_ty = build_pointer_type (element_type);
-  Backend::typed_identifier data_field ("data", data_field_ty, Location ());
-  fields.push_back (std::move (data_field));
-
-  // lookup usize
-  TyTy::BaseType *usize = nullptr;
-  bool ok = ctx->get_tyctx ()->lookup_builtin ("usize", &usize);
-  rust_assert (ok);
-
-  tree len_field_ty = TyTyResolveCompile::compile (ctx, usize);
-  Backend::typed_identifier len_field ("len", len_field_ty, Location ());
-  fields.push_back (std::move (len_field));
-
-  tree type_record = ctx->get_backend ()->struct_type (fields);
+  tree type_record = create_slice_type_record (type);
 
   std::string named_struct_str
     = std::string ("[") + type.get_element_type ()->get_name () + "]";
@@ -536,6 +524,21 @@ TyTyResolveCompile::visit (const TyTy::CharType &type)
 void
 TyTyResolveCompile::visit (const TyTy::ReferenceType &type)
 {
+  const TyTy::SliceType *slice = nullptr;
+  if (type.is_dyn_slice_type (&slice))
+    {
+      tree type_record = create_slice_type_record (*slice);
+      std::string dyn_slice_type_str
+	= std::string (type.is_mutable () ? "&mut " : "&") + "["
+	  + slice->get_element_type ()->get_name () + "]";
+
+      translated
+	= ctx->get_backend ()->named_type (dyn_slice_type_str, type_record,
+					   slice->get_locus ());
+
+      return;
+    }
+
   tree base_compiled_type
     = TyTyResolveCompile::compile (ctx, type.get_base (), trait_object_mode);
   if (type.is_mutable ())
@@ -552,6 +555,21 @@ TyTyResolveCompile::visit (const TyTy::ReferenceType &type)
 void
 TyTyResolveCompile::visit (const TyTy::PointerType &type)
 {
+  const TyTy::SliceType *slice = nullptr;
+  if (type.is_dyn_slice_type (&slice))
+    {
+      tree type_record = create_slice_type_record (*slice);
+      std::string dyn_slice_type_str
+	= std::string (type.is_mutable () ? "*mut " : "*const ") + "["
+	  + slice->get_element_type ()->get_name () + "]";
+
+      translated
+	= ctx->get_backend ()->named_type (dyn_slice_type_str, type_record,
+					   slice->get_locus ());
+
+      return;
+    }
+
   tree base_compiled_type
     = TyTyResolveCompile::compile (ctx, type.get_base (), trait_object_mode);
   if (type.is_mutable ())
@@ -615,5 +633,29 @@ TyTyResolveCompile::visit (const TyTy::DynamicObjectType &type)
 						type.get_ident ().locus);
 }
 
+tree
+TyTyResolveCompile::create_slice_type_record (const TyTy::SliceType &type)
+{
+  // lookup usize
+  TyTy::BaseType *usize = nullptr;
+  bool ok = ctx->get_tyctx ()->lookup_builtin ("usize", &usize);
+  rust_assert (ok);
+
+  tree element_type
+    = TyTyResolveCompile::compile (ctx, type.get_element_type ());
+  tree data_field_ty = build_pointer_type (element_type);
+  Backend::typed_identifier data_field ("data", data_field_ty,
+					type.get_locus ());
+
+  tree len_field_ty = TyTyResolveCompile::compile (ctx, usize);
+  Backend::typed_identifier len_field ("len", len_field_ty, type.get_locus ());
+
+  tree record = ctx->get_backend ()->struct_type ({data_field, len_field});
+  SLICE_FLAG (record) = 1;
+  TYPE_MAIN_VARIANT (record) = ctx->insert_main_variant (record);
+
+  return record;
+}
+
 } // namespace Compile
 } // namespace Rust
diff --git a/gcc/rust/backend/rust-compile-type.h b/gcc/rust/backend/rust-compile-type.h
index 262b8fc..aefacea 100644
--- a/gcc/rust/backend/rust-compile-type.h
+++ b/gcc/rust/backend/rust-compile-type.h
@@ -60,11 +60,11 @@ public:
 public:
   static hashval_t type_hasher (tree type);
 
+protected:
+  tree create_slice_type_record (const TyTy::SliceType &type);
+
 private:
-  TyTyResolveCompile (Context *ctx, bool trait_object_mode)
-    : ctx (ctx), trait_object_mode (trait_object_mode),
-      translated (error_mark_node), recurisve_ops (0)
-  {}
+  TyTyResolveCompile (Context *ctx, bool trait_object_mode);
 
   Context *ctx;
   bool trait_object_mode;
diff --git a/gcc/rust/backend/rust-compile.cc b/gcc/rust/backend/rust-compile.cc
index d9349d5..18a2df6 100644
--- a/gcc/rust/backend/rust-compile.cc
+++ b/gcc/rust/backend/rust-compile.cc
@@ -218,6 +218,11 @@ HIRCompileBase::coercion_site (tree rvalue, const TyTy::BaseType *rval,
 	= static_cast<const TyTy::ReferenceType *> (expected);
       const TyTy::ReferenceType *act
 	= static_cast<const TyTy::ReferenceType *> (actual);
+      if (act->is_dyn_slice_type ())
+	{
+	  // nothing to do
+	  return rvalue;
+	}
 
       tree expected_type = TyTyResolveCompile::compile (ctx, act->get_base ());
       tree deref_rvalue
@@ -227,6 +232,8 @@ HIRCompileBase::coercion_site (tree rvalue, const TyTy::BaseType *rval,
       tree coerced
 	= coercion_site (deref_rvalue, act->get_base (), exp->get_base (),
 			 lvalue_locus, rvalue_locus);
+      if (exp->is_dyn_slice_type () && SLICE_TYPE_P (TREE_TYPE (coerced)))
+	return coerced;
 
       return address_expression (coerced,
 				 build_reference_type (TREE_TYPE (coerced)),
@@ -249,6 +256,12 @@ HIRCompileBase::coercion_site (tree rvalue, const TyTy::BaseType *rval,
 	{
 	  const TyTy::ReferenceType *act
 	    = static_cast<const TyTy::ReferenceType *> (actual);
+	  if (act->is_dyn_slice_type ())
+	    {
+	      // nothing to do
+	      return rvalue;
+	    }
+
 	  actual_base = act->get_base ();
 	  expected_type = TyTyResolveCompile::compile (ctx, act->get_base ());
 	}
@@ -256,6 +269,12 @@ HIRCompileBase::coercion_site (tree rvalue, const TyTy::BaseType *rval,
 	{
 	  const TyTy::PointerType *act
 	    = static_cast<const TyTy::PointerType *> (actual);
+	  if (act->is_dyn_slice_type ())
+	    {
+	      // nothing to do
+	      return rvalue;
+	    }
+
 	  actual_base = act->get_base ();
 	  expected_type = TyTyResolveCompile::compile (ctx, act->get_base ());
 	}
diff --git a/gcc/rust/backend/rust-tree.h b/gcc/rust/backend/rust-tree.h
index c50e090..2b480ad 100644
--- a/gcc/rust/backend/rust-tree.h
+++ b/gcc/rust/backend/rust-tree.h
@@ -74,6 +74,12 @@
   (INDIRECT_REF_P (NODE) && TREE_TYPE (TREE_OPERAND (NODE, 0))                 \
    && TYPE_REF_P (TREE_TYPE (TREE_OPERAND ((NODE), 0))))
 
+// this is a helper to differentiate RECORD types between actual records and
+// slices
+#define SLICE_FLAG TREE_LANG_FLAG_0
+#define SLICE_TYPE_P(TYPE)                                                     \
+  (TREE_CODE (TYPE) == RECORD_TYPE && TREE_LANG_FLAG_0 (TYPE))
+
 namespace Rust {
 
 // forked from gcc/cp/cvt.cc convert_to_void