From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2122) id 704EA3947404; Tue, 2 May 2023 20:26:40 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 704EA3947404 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1683059200; bh=TJek8SHAvt9TbZVwIRdd9W9DnGq7P002VHVnARzwCPg=; h=From:To:Subject:Date:From; b=hPmODRsTTeVtxuPOv9u8RY1P3I0mlOxDNa7t3NNT+wooIonmVHxjfkqLGeefgmMZW 9gMAaaYlRHwl1BlPbps7i6iRa+hhSRsLOkB9PHvGfj0rv2CYVEcBaH/kBbKmtavek5 8lG+RMUL9B/ZB8beC898rF+a84F+FAFDGrypZOY4= MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Jason Merrill To: gcc-cvs@gcc.gnu.org Subject: [gcc r14-409] c++: std::variant slow to compile [PR109678] X-Act-Checkin: gcc X-Git-Author: Jason Merrill X-Git-Refname: refs/heads/trunk X-Git-Oldrev: bc24c51c0ccd64617864897ad071c98004ffc0a4 X-Git-Newrev: 4b8d0d4d7fd245ef85c7801e7838845502a5a61d Message-Id: <20230502202640.704EA3947404@sourceware.org> Date: Tue, 2 May 2023 20:26:40 +0000 (GMT) List-Id: https://gcc.gnu.org/g:4b8d0d4d7fd245ef85c7801e7838845502a5a61d commit r14-409-g4b8d0d4d7fd245ef85c7801e7838845502a5a61d Author: Jason Merrill Date: Mon May 1 17:41:44 2023 -0400 c++: std::variant slow to compile [PR109678] Here, when dealing with a class with a complex subobject structure, we would try and fail to find the relevant FIELD_DECL for an empty base before giving up. And we would do this at each level, in a combinatorially problematic way. Instead, we should check for an empty base first. PR c++/109678 gcc/cp/ChangeLog: * constexpr.cc (cxx_fold_indirect_ref_1): Handle empty base first. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/variant1.C: New test. Diff: --- gcc/cp/constexpr.cc | 23 +++++++++-------- gcc/testsuite/g++.dg/cpp1z/variant1.C | 47 +++++++++++++++++++++++++++++++++++ 2 files changed, 60 insertions(+), 10 deletions(-) diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index d1097764b10..37d1c444c9e 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -5446,6 +5446,19 @@ cxx_fold_indirect_ref_1 (const constexpr_ctx *ctx, location_t loc, tree type, return ret; } } + + /* Handle conversion to an empty base class, which is represented with a + NOP_EXPR. Do this before spelunking into the non-empty subobjects, + which is likely to be a waste of time (109678). */ + if (is_empty_class (type) + && CLASS_TYPE_P (optype) + && DERIVED_FROM_P (type, optype)) + { + if (empty_base) + *empty_base = true; + return op; + } + for (tree field = TYPE_FIELDS (optype); field; field = DECL_CHAIN (field)) if (TREE_CODE (field) == FIELD_DECL @@ -5468,16 +5481,6 @@ cxx_fold_indirect_ref_1 (const constexpr_ctx *ctx, location_t loc, tree type, return ret; } } - /* Also handle conversion to an empty base class, which - is represented with a NOP_EXPR. */ - if (is_empty_class (type) - && CLASS_TYPE_P (optype) - && DERIVED_FROM_P (type, optype)) - { - if (empty_base) - *empty_base = true; - return op; - } } return NULL_TREE; diff --git a/gcc/testsuite/g++.dg/cpp1z/variant1.C b/gcc/testsuite/g++.dg/cpp1z/variant1.C new file mode 100644 index 00000000000..9b18cc233ca --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/variant1.C @@ -0,0 +1,47 @@ +// PR c++/109678 +// With the bug, compiling this testcase takes more than the typical timeout. +// { dg-do compile { target c++17 } } + +#include + +struct A {}; +struct B {}; +struct C {}; +struct D {}; +struct E {}; +struct F {}; +struct G {}; +struct H {}; +struct I {}; +struct J {}; +struct K {}; +struct L {}; +struct M {}; +struct N {}; +struct O {}; +struct P {}; +struct Q {}; +struct R {}; +struct S {}; +struct T {}; +struct U {}; +struct V {}; +struct W { + // gcc13 + compiler explorer = 20000ms + // gcc12.2 + compiler explorer = 400ms + int i; +}; +struct X {}; +struct Y {}; +struct Z {}; + +using Foo = std::variant; + +struct Bar { + Foo f; + static Bar dummy() { + // issue is triggered by this initialization + return {Z{}}; + // return {A{}}; // would be very quick + } +};