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Fix issues about block expression evaluation #380

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Merged
merged 3 commits into from
Apr 23, 2021
Merged

Fix issues about block expression evaluation #380

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c5fdf8c
The trailing expression is not necessarily without a block
lrh2000 Apr 10, 2021
3aeb9f4
Introduce limited support for the never type
lrh2000 Apr 10, 2021
28895c1
Merge branch 'origin/master'
lrh2000 Apr 22, 2021
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10 changes: 5 additions & 5 deletions gcc/rust/ast/rust-expr.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2828,7 +2828,7 @@ class BlockExpr : public ExprWithBlock
std::vector<Attribute> outer_attrs;
std::vector<Attribute> inner_attrs;
std::vector<std::unique_ptr<Stmt> > statements;
std::unique_ptr<ExprWithoutBlock> expr;
std::unique_ptr<Expr> expr;
Location locus;
bool marked_for_strip = false;

Expand All @@ -2842,7 +2842,7 @@ class BlockExpr : public ExprWithBlock
bool has_tail_expr () const { return expr != nullptr; }

BlockExpr (std::vector<std::unique_ptr<Stmt> > block_statements,
std::unique_ptr<ExprWithoutBlock> block_expr,
std::unique_ptr<Expr> block_expr,
std::vector<Attribute> inner_attribs,
std::vector<Attribute> outer_attribs, Location locus)
: outer_attrs (std::move (outer_attribs)),
Expand All @@ -2859,7 +2859,7 @@ class BlockExpr : public ExprWithBlock
{
// guard to protect from null pointer dereference
if (other.expr != nullptr)
expr = other.expr->clone_expr_without_block ();
expr = other.expr->clone_expr ();

statements.reserve (other.statements.size ());
for (const auto &e : other.statements)
Expand All @@ -2877,7 +2877,7 @@ class BlockExpr : public ExprWithBlock

// guard to protect from null pointer dereference
if (other.expr != nullptr)
expr = other.expr->clone_expr_without_block ();
expr = other.expr->clone_expr ();
else
expr = nullptr;

Expand Down Expand Up @@ -2929,7 +2929,7 @@ class BlockExpr : public ExprWithBlock
std::vector<std::unique_ptr<Stmt> > &get_statements () { return statements; }

// TODO: is this better? Or is a "vis_block" better?
std::unique_ptr<ExprWithoutBlock> &get_tail_expr ()
std::unique_ptr<Expr> &get_tail_expr ()
{
rust_assert (has_tail_expr ());
return expr;
Expand Down
9 changes: 7 additions & 2 deletions gcc/rust/ast/rust-stmt.h
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Expand Up @@ -269,14 +269,17 @@ class ExprStmtWithoutBlock : public ExprStmt
class ExprStmtWithBlock : public ExprStmt
{
std::unique_ptr<ExprWithBlock> expr;
bool semicolon_followed;

public:
std::string as_string () const override;

std::vector<LetStmt *> locals;

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Is this the right grammar? https://doc.rust-lang.org/stable/reference/statements.html

@SimplyTheOther what do you think?

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I think it does look like what @yizhepku mentioned in #317 which seems right

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"An expression that consists of only a block expression or control flow expression, if used in a context where a statement is permitted, can omit the trailing semicolon. [...] When the trailing semicolon is omitted, the result must be type ()." quoted from https://doc.rust-lang.org/stable/reference/statements.html. So I think it is right.

ExprStmtWithBlock (std::unique_ptr<ExprWithBlock> expr, Location locus)
: ExprStmt (locus), expr (std::move (expr))
ExprStmtWithBlock (std::unique_ptr<ExprWithBlock> expr, Location locus,
bool semicolon_followed)
: ExprStmt (locus), expr (std::move (expr)),
semicolon_followed (semicolon_followed)
{}

// Copy constructor with clone
Expand Down Expand Up @@ -318,6 +321,8 @@ class ExprStmtWithBlock : public ExprStmt
return expr;
}

bool is_semicolon_followed () const { return semicolon_followed; }

protected:
/* Use covariance to implement clone function as returning this object rather
* than base */
Expand Down
5 changes: 5 additions & 0 deletions gcc/rust/backend/rust-compile-context.h
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Expand Up @@ -501,6 +501,11 @@ class TyTyResolveCompile : public TyTy::TyVisitor
translated = compiled_type;
}

void visit (TyTy::NeverType &) override
{
translated = ctx->get_backend ()->void_type ();
}

private:
TyTyResolveCompile (Context *ctx) : ctx (ctx), translated (nullptr) {}

Expand Down
5 changes: 5 additions & 0 deletions gcc/rust/backend/rust-compile-tyty.h
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Expand Up @@ -222,6 +222,11 @@ class TyTyCompile : public TyTy::TyVisitor
= 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),
Expand Down
9 changes: 4 additions & 5 deletions gcc/rust/backend/rust-compile.cc
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Expand Up @@ -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
Expand Down Expand Up @@ -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);
Expand All @@ -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);
Expand Down
3 changes: 2 additions & 1 deletion gcc/rust/hir/rust-ast-lower-stmt.h
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Expand Up @@ -59,7 +59,8 @@ class ASTLoweringStmt : public ASTLoweringBase
translated
= new HIR::ExprStmtWithBlock (mapping,
std::unique_ptr<HIR::ExprWithBlock> (expr),
stmt.get_locus ());
stmt.get_locus (),
!stmt.is_semicolon_followed ());
mappings->insert_location (crate_num, mapping.get_hirid (),
stmt.get_locus ());
mappings->insert_hir_stmt (crate_num, mapping.get_hirid (), translated);
Expand Down
2 changes: 1 addition & 1 deletion gcc/rust/hir/rust-ast-lower.cc
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Expand Up @@ -90,7 +90,7 @@ ASTLoweringBlock::visit (AST::BlockExpr &expr)
return true;
});

bool tail_reachable = expr.has_tail_expr () && !block_did_terminate;
bool tail_reachable = !block_did_terminate;
if (expr.has_tail_expr () && block_did_terminate)
{
// warning unreachable tail expressions
Expand Down
12 changes: 6 additions & 6 deletions gcc/rust/hir/tree/rust-hir-expr.h
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Expand Up @@ -2489,7 +2489,7 @@ class BlockExpr : public ExprWithBlock
std::vector<Attribute> inner_attrs;

std::vector<std::unique_ptr<Stmt> > statements;
std::unique_ptr<ExprWithoutBlock> expr; // inlined from Statements
std::unique_ptr<Expr> expr; // inlined from Statements

bool tail_reachable;
Location locus;
Expand All @@ -2502,11 +2502,11 @@ class BlockExpr : public ExprWithBlock
// Returns whether the block contains an expression
bool has_expr () const { return expr != nullptr; }

bool tail_expr_reachable () const { return tail_reachable; }
bool is_tail_reachable () const { return tail_reachable; }

BlockExpr (Analysis::NodeMapping mappings,
std::vector<std::unique_ptr<Stmt> > block_statements,
std::unique_ptr<ExprWithoutBlock> block_expr, bool tail_reachable,
std::unique_ptr<Expr> block_expr, bool tail_reachable,
std::vector<Attribute> inner_attribs,
std::vector<Attribute> outer_attribs, Location locus)
: ExprWithBlock (std::move (mappings), std::move (outer_attribs)),
Expand All @@ -2522,7 +2522,7 @@ class BlockExpr : public ExprWithBlock
{
// guard to protect from null pointer dereference
if (other.expr != nullptr)
expr = other.expr->clone_expr_without_block ();
expr = other.expr->clone_expr ();

statements.reserve (other.statements.size ());
for (const auto &e : other.statements)
Expand All @@ -2534,7 +2534,7 @@ class BlockExpr : public ExprWithBlock
{
ExprWithBlock::operator= (other);
// statements = other.statements;
expr = other.expr->clone_expr_without_block ();
expr = other.expr->clone_expr ();
inner_attrs = other.inner_attrs;
locus = other.locus;
// outer_attrs = other.outer_attrs;
Expand Down Expand Up @@ -2580,7 +2580,7 @@ class BlockExpr : public ExprWithBlock
return statements[statements.size () - 1]->get_locus_slow ();
}

std::unique_ptr<ExprWithoutBlock> &get_final_expr () { return expr; }
std::unique_ptr<Expr> &get_final_expr () { return expr; }

std::vector<std::unique_ptr<Stmt> > &get_statements () { return statements; }

Expand Down
9 changes: 7 additions & 2 deletions gcc/rust/hir/tree/rust-hir-stmt.h
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Original file line number Diff line number Diff line change
Expand Up @@ -193,13 +193,16 @@ class ExprStmtWithoutBlock : public ExprStmt
class ExprStmtWithBlock : public ExprStmt
{
std::unique_ptr<ExprWithBlock> expr;
bool must_be_unit;

public:
std::string as_string () const override;

ExprStmtWithBlock (Analysis::NodeMapping mappings,
std::unique_ptr<ExprWithBlock> expr, Location locus)
: ExprStmt (std::move (mappings), locus), expr (std::move (expr))
std::unique_ptr<ExprWithBlock> expr, Location locus,
bool must_be_unit)
: ExprStmt (std::move (mappings), locus), expr (std::move (expr)),
must_be_unit (must_be_unit)
{}

// Copy constructor with clone
Expand All @@ -224,6 +227,8 @@ class ExprStmtWithBlock : public ExprStmt

ExprWithBlock *get_expr () { return expr.get (); }

bool is_unit_check_needed () const override { return must_be_unit; }

protected:
/* Use covariance to implement clone function as returning this object rather
* than base */
Expand Down
2 changes: 2 additions & 0 deletions gcc/rust/hir/tree/rust-hir.h
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Expand Up @@ -723,6 +723,8 @@ class Stmt
* methods. */
virtual Location get_locus_slow () const { return Location (); }

virtual bool is_unit_check_needed () const { return false; }

const Analysis::NodeMapping &get_mappings () const { return mappings; }

protected:
Expand Down
61 changes: 44 additions & 17 deletions gcc/rust/parse/rust-parse-impl.h
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Expand Up @@ -7022,11 +7022,9 @@ Parser<ManagedTokenSource>::parse_expr_stmt (
}
}

/* Parses a expression statement containing an expression with block.
* Disambiguates internally. */
template <typename ManagedTokenSource>
std::unique_ptr<AST::ExprStmtWithBlock>
Parser<ManagedTokenSource>::parse_expr_stmt_with_block (
std::unique_ptr<AST::ExprWithBlock>
Parser<ManagedTokenSource>::parse_expr_with_block (
std::vector<AST::Attribute> outer_attrs)
{
std::unique_ptr<AST::ExprWithBlock> expr_parsed = nullptr;
Expand Down Expand Up @@ -7113,9 +7111,23 @@ Parser<ManagedTokenSource>::parse_expr_stmt_with_block (
return nullptr;
}

return expr_parsed;
}

/* Parses a expression statement containing an expression with block.
* Disambiguates internally. */
template <typename ManagedTokenSource>
std::unique_ptr<AST::ExprStmtWithBlock>
Parser<ManagedTokenSource>::parse_expr_stmt_with_block (
std::vector<AST::Attribute> outer_attrs)
{
auto expr_parsed = parse_expr_with_block (std::move (outer_attrs));
auto locus = expr_parsed->get_locus ();

// return expr stmt created from expr
return std::unique_ptr<AST::ExprStmtWithBlock> (
new AST::ExprStmtWithBlock (std::move (expr_parsed), t->get_locus ()));
new AST::ExprStmtWithBlock (std::move (expr_parsed), locus,
lexer.peek_token ()->get_id () == SEMICOLON));
}

/* Parses an expression statement containing an expression without block.
Expand Down Expand Up @@ -7286,7 +7298,7 @@ Parser<ManagedTokenSource>::parse_block_expr (

// parse statements and expression
std::vector<std::unique_ptr<AST::Stmt>> stmts;
std::unique_ptr<AST::ExprWithoutBlock> expr = nullptr;
std::unique_ptr<AST::Expr> expr = nullptr;

const_TokenPtr t = lexer.peek_token ();
while (t->get_id () != RIGHT_CURLY)
Expand Down Expand Up @@ -11438,6 +11450,29 @@ Parser<ManagedTokenSource>::parse_struct_pattern_field_partial (
}
}

template <typename ManagedTokenSource>
ExprOrStmt
Parser<ManagedTokenSource>::parse_stmt_or_expr_with_block (
std::vector<AST::Attribute> outer_attrs)
{
auto expr = parse_expr_with_block (std::move (outer_attrs));
auto tok = lexer.peek_token ();

// tail expr in a block expr
if (tok->get_id () == RIGHT_CURLY)
return ExprOrStmt (std::move (expr));

// internal block expr must either have semicolons followed, or evaluate to ()
auto locus = expr->get_locus_slow ();
std::unique_ptr<AST::ExprStmtWithBlock> stmt (
new AST::ExprStmtWithBlock (std::move (expr), locus,
tok->get_id () == SEMICOLON));
if (tok->get_id () == SEMICOLON)
lexer.skip_token ();

return ExprOrStmt (std::move (stmt));
}

/* Parses a statement or expression (depending on whether a trailing semicolon
* exists). Useful for block expressions where it cannot be determined through
* lookahead whether it is a statement or expression to be parsed. */
Expand Down Expand Up @@ -11508,9 +11543,7 @@ Parser<ManagedTokenSource>::parse_stmt_or_expr_without_block ()
{
case LEFT_CURLY: {
// unsafe block
std::unique_ptr<AST::ExprStmtWithBlock> stmt (
parse_expr_stmt_with_block (std::move (outer_attrs)));
return ExprOrStmt (std::move (stmt));
return parse_stmt_or_expr_with_block (std::move (outer_attrs));
}
case TRAIT: {
// unsafe trait
Expand Down Expand Up @@ -11577,11 +11610,7 @@ Parser<ManagedTokenSource>::parse_stmt_or_expr_without_block ()
case MATCH_TOK:
case LEFT_CURLY:
case ASYNC: {
// all expressions with block, so cannot be final expr without block in
// function
std::unique_ptr<AST::ExprStmtWithBlock> stmt (
parse_expr_stmt_with_block (std::move (outer_attrs)));
return ExprOrStmt (std::move (stmt));
return parse_stmt_or_expr_with_block (std::move (outer_attrs));
}
case LIFETIME: {
/* FIXME: are there any expressions without blocks that can have
Expand All @@ -11592,9 +11621,7 @@ Parser<ManagedTokenSource>::parse_stmt_or_expr_without_block ()
&& (t2->get_id () == LOOP || t2->get_id () == WHILE
|| t2->get_id () == FOR))
{
std::unique_ptr<AST::ExprStmtWithBlock> stmt (
parse_expr_stmt_with_block (std::move (outer_attrs)));
return ExprOrStmt (std::move (stmt));
return parse_stmt_or_expr_with_block (std::move (outer_attrs));
}
else
{
Expand Down
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