From 8743680541b8aeefdecba01b1960509a8d184202 Mon Sep 17 00:00:00 2001 From: Cherry Zhang Date: Thu, 9 May 2019 21:24:56 +0000 Subject: compiler: avoid copy for string([]byte) conversion used in map keys If a string([]byte) conversion is used immediately as a key for a map read, we don't need to copy the backing store of the byte slice, as mapaccess does not keep a reference to it. The gc compiler does more than this: it also avoids the copy if the map key is a composite literal that contains the conversion as a field, like, T{ ... { ..., string(b), ... }, ... }. For now, we just optimize the simple case, which is probably most common. Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/176197 * go.dg/mapstring.go: New test. From-SVN: r271044 --- gcc/go/gofrontend/MERGE | 2 +- gcc/go/gofrontend/expressions.cc | 7 +++++++ gcc/go/gofrontend/statements.cc | 7 +++++++ 3 files changed, 15 insertions(+), 1 deletion(-) (limited to 'gcc/go') diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE index f6f28a3..b601770 100644 --- a/gcc/go/gofrontend/MERGE +++ b/gcc/go/gofrontend/MERGE @@ -1,4 +1,4 @@ -9c8581187b1c1a30036263728370f31cb846a274 +3dbf51c01c5d0acbf9ae47f77166fa9935881749 The first line of this file holds the git revision number of the last merge done from the gofrontend repository. diff --git a/gcc/go/gofrontend/expressions.cc b/gcc/go/gofrontend/expressions.cc index 2c1286c..929571b 100644 --- a/gcc/go/gofrontend/expressions.cc +++ b/gcc/go/gofrontend/expressions.cc @@ -12158,6 +12158,13 @@ Map_index_expression::do_flatten(Gogo* gogo, Named_object*, return Expression::make_error(loc); } + // Avoid copy for string([]byte) conversions used in map keys. + // mapaccess doesn't keep the reference, so this is safe. + Type_conversion_expression* ce = this->index_->conversion_expression(); + if (ce != NULL && ce->type()->is_string_type() + && ce->expr()->type()->is_slice_type()) + ce->set_no_copy(true); + if (!Type::are_identical(mt->key_type(), this->index_->type(), Type::COMPARE_ERRORS | Type::COMPARE_TAGS, NULL)) diff --git a/gcc/go/gofrontend/statements.cc b/gcc/go/gofrontend/statements.cc index 2e2d039..67ab184 100644 --- a/gcc/go/gofrontend/statements.cc +++ b/gcc/go/gofrontend/statements.cc @@ -1307,6 +1307,13 @@ Tuple_map_assignment_statement::do_lower(Gogo* gogo, Named_object*, if (map_type == NULL) return Statement::make_error_statement(loc); + // Avoid copy for string([]byte) conversions used in map keys. + // mapaccess doesn't keep the reference, so this is safe. + Type_conversion_expression* ce = map_index->index()->conversion_expression(); + if (ce != NULL && ce->type()->is_string_type() + && ce->expr()->type()->is_slice_type()) + ce->set_no_copy(true); + Block* b = new Block(enclosing, loc); // Move out any subexpressions to make sure that functions are -- cgit v1.1