Merge #380

380: Fix issues about block expression evaluation r=philberty a=lrh2000

I've tried my best to split https://github.com/Rust-GCC/gccrs/pull/364. Its core part is here. All unrelated fixes should have been removed and I will make them separate PRs, but this PR still has to contain 2 commits and introduce limited support for the never type.

https://github.com/Rust-GCC/gccrs/blob/935aff52a66a70e1e96f0a6aa7e0ad37eda3f93c/gcc/testsuite/rust.test/compile/deadcode1.rs#L7-L15

https://github.com/Rust-GCC/gccrs/blob/935aff52a66a70e1e96f0a6aa7e0ad37eda3f93c/gcc/testsuite/rust.test/compile/implicit_returns1.rs#L44-L50

The reason is that the above two tests failed to pass simultaneously after the first commit. The first test requires the `if/else` expression resolves to `()` but the second test requires the `if/else` expression resolves to `<integer>`. They are conflicted.

I wonder whether or not this PR is OK, and anyway thanks for your review.

Co-authored-by: lrh2000 <lrh2000@pku.edu.cn>

3 files changed, 14 insertions, 5 deletions

diff --git a/gcc/rust/backend/rust-compile-context.h b/gcc/rust/backend/rust-compile-context.h
index 226cec6..11e791c 100644
--- a/gcc/rust/backend/rust-compile-context.h
+++ b/gcc/rust/backend/rust-compile-context.h
@@ -501,6 +501,11 @@ public:
     translated = compiled_type;
   }
 
+  void visit (TyTy::NeverType &) override
+  {
+    translated = ctx->get_backend ()->void_type ();
+  }
+
 private:
   TyTyResolveCompile (Context *ctx) : ctx (ctx), translated (nullptr) {}
 
diff --git a/gcc/rust/backend/rust-compile-tyty.h b/gcc/rust/backend/rust-compile-tyty.h
index 28db289..ba98ac0 100644
--- a/gcc/rust/backend/rust-compile-tyty.h
+++ b/gcc/rust/backend/rust-compile-tyty.h
@@ -222,6 +222,11 @@ public:
       = backend->named_type ("str", raw_str, Linemap::predeclared_location ());
   }
 
+  void visit (TyTy::NeverType &) override
+  {
+    translated = backend->void_type ();
+  }
+
 private:
   TyTyCompile (::Backend *backend)
     : backend (backend), translated (nullptr),
diff --git a/gcc/rust/backend/rust-compile.cc b/gcc/rust/backend/rust-compile.cc
index a2f5247..9375dd0 100644
--- a/gcc/rust/backend/rust-compile.cc
+++ b/gcc/rust/backend/rust-compile.cc
@@ -256,7 +256,7 @@ CompileBlock::visit (HIR::BlockExpr &expr)
 	}
     }
 
-  if (expr.has_expr () && expr.tail_expr_reachable ())
+  if (expr.has_expr ())
     {
       // the previous passes will ensure this is a valid return
       // dead code elimination should remove any bad trailing expressions
@@ -410,15 +410,14 @@ HIRCompileBase::compile_function_body (
 	}
     }
 
-  if (function_body->has_expr () && function_body->tail_expr_reachable ())
+  if (function_body->has_expr ())
     {
       // the previous passes will ensure this is a valid return
       // dead code elimination should remove any bad trailing expressions
       Bexpression *compiled_expr
 	= CompileExpr::Compile (function_body->expr.get (), ctx);
-      rust_assert (compiled_expr != nullptr);
 
-      if (has_return_type)
+      if (has_return_type && compiled_expr)
 	{
 	  std::vector<Bexpression *> retstmts;
 	  retstmts.push_back (compiled_expr);
@@ -428,7 +427,7 @@ HIRCompileBase::compile_function_body (
 	    function_body->get_final_expr ()->get_locus_slow ());
 	  ctx->add_statement (ret);
 	}
-      else
+      else if (compiled_expr)
 	{
 	  Bstatement *final_stmt
 	    = ctx->get_backend ()->expression_statement (fndecl, compiled_expr);