From 9c5505a35d9d71705464f9254f55407192d31ec3 Mon Sep 17 00:00:00 2001 From: Jan Hubicka Date: Sun, 30 Mar 2025 23:49:49 +0200 Subject: Optimize string constructor this patch improves code generation on string constructors. We currently have _M_construct which takes as a parameter two iterators (begin/end pointers to other string) and produces new string. This patch adds special case of constructor where instead of begining/end pointers we readily know the string size and also special case when we know that source is 0 terminated. This happens commonly when producing stirng copies. Moreover currently ipa-prop is not able to propagate information that beg-end is known constant (copied string size) which makes it impossible for inliner to spot the common case where string size is known to be shorter than 15 bytes and fits in local buffer. Finally I made new constructor inline. Because it is explicitely instantiated without C++20 constexpr we do not produce implicit instantiation (as required by standard) which prevents inlining, ipa-modref and any other IPA analysis to happen. I think we need to make many of the other functions inline, since optimization accross string manipulation is quite important. There is PR94960 to track this issue. Bootstrapped/regtested x86_64-linux, OK? libstdc++-v3/ChangeLog: PR tree-optimization/103827 PR tree-optimization/80331 PR tree-optimization/87502 * config/abi/pre/gnu.ver: Add version for _M_construct * include/bits/basic_string.h: (basic_string::_M_construct): Declare. (basic_string constructors): Use it. * include/bits/basic_string.tcc: (basic_string::_M_construct): New template. * src/c++11/string-inst.cc: Instantated S::_M_construct. gcc/testsuite/ChangeLog: * g++.dg/tree-ssa/pr80331.C: New test. * g++.dg/tree-ssa/pr87502.C: New test. --- gcc/testsuite/g++.dg/tree-ssa/pr80331.C | 8 ++++++++ gcc/testsuite/g++.dg/tree-ssa/pr87502.C | 15 +++++++++++++++ 2 files changed, 23 insertions(+) create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr80331.C create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr87502.C (limited to 'gcc') diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr80331.C b/gcc/testsuite/g++.dg/tree-ssa/pr80331.C new file mode 100644 index 0000000..8503450 --- /dev/null +++ b/gcc/testsuite/g++.dg/tree-ssa/pr80331.C @@ -0,0 +1,8 @@ +// { dg-do compile } +// { dg-additional-options "-O2 -fdump-tree-optimized" } +#include +int sain() { + const std::string remove_me("remove_me"); + return 0; +} +// { dg-final { scan-tree-dump-not "remove_me" "optimized" } } diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr87502.C b/gcc/testsuite/g++.dg/tree-ssa/pr87502.C new file mode 100644 index 0000000..ad3e9d2 --- /dev/null +++ b/gcc/testsuite/g++.dg/tree-ssa/pr87502.C @@ -0,0 +1,15 @@ +// { dg-do compile } +// { dg-additional-options "-O2 -fdump-tree-optimized" } +#include + + +__attribute__ ((pure)) +extern int foo (const std::string &); + +int +bar () +{ + return foo ("abc") + foo (std::string("abc")); +} +// We used to add terminating zero explicitely instead of using fact +// that memcpy source is already 0 terminated. -- cgit v1.1