From 0397f495c0c46a7e4ebe304e6ebf14d85fb76dc7 Mon Sep 17 00:00:00 2001 From: Roman Lebedev Date: Mon, 25 Feb 2019 20:51:49 +0000 Subject: [Support] Make raw_string_ostream unbuffered Summary: In D58580 i have noted that `llvm::to_string()` is a memory hog. It uses `raw_string_ostream`, and since it was buffered, every `raw_string_ostream` had a cost of `BUFSIZ` bytes (which is `8192` at least here). So every `llvm::to_string()` call, even to just print an `int`, costed `8192` bytes. In D58580, getting rid of that buffering //had// significant performance and memory consumption improvements for `llvm-xray convert`. Similarly, in D58580 @rnk pointed out that the `raw_svector_ostream` is already unbuffered, and `write_unsigned_impl` and friends do internal buffering. So it should be ok performance-wise to just make the `raw_string_ostream` itself unbuffered. Here, i don't have any perf measurements. Another letdown is that i'm leaving a loose-end - not deleting the `flush()` method. I don't expect that cleanup to be anything more than just fixing every new compiler error, but i'm presently unable to do that. Will look into that later. Reviewers: rnk, zturner Reviewed By: rnk Subscribers: kristina, jdoerfert, llvm-commits, rnk Tags: #llvm Differential Revision: https://reviews.llvm.org/D58643 llvm-svn: 354819 --- llvm/include/llvm/Support/raw_ostream.h | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/llvm/include/llvm/Support/raw_ostream.h b/llvm/include/llvm/Support/raw_ostream.h index 48bb623b063..199dfe2844f 100644 --- a/llvm/include/llvm/Support/raw_ostream.h +++ b/llvm/include/llvm/Support/raw_ostream.h @@ -479,6 +479,9 @@ raw_ostream &nulls(); /// A raw_ostream that writes to an std::string. This is a simple adaptor /// class. This class does not encounter output errors. +/// raw_string_ostream operates without a buffer, delegating all memory +/// management to the std::string. Thus the std::string is always up-to-date, +/// may be used directly and there is no need to call flush(). class raw_string_ostream : public raw_ostream { std::string &OS; @@ -490,13 +493,16 @@ class raw_string_ostream : public raw_ostream { uint64_t current_pos() const override { return OS.size(); } public: - explicit raw_string_ostream(std::string &O) : OS(O) {} + explicit raw_string_ostream(std::string &O) + : raw_ostream(/*Unbuffered=*/true), OS(O) {} + ~raw_string_ostream() override; - /// Flushes the stream contents to the target string and returns the string's - /// reference. + // FIXME: uncomment and deal with the fallout. + // void flush() = delete; + + /// Returns the string's reference. std::string& str() { - flush(); return OS; } }; -- cgit v1.2.3