From 37048d04d8eefd24af4871bd9428f389eaad0abe Mon Sep 17 00:00:00 2001 From: serge-sans-paille Date: Wed, 23 Nov 2022 07:45:59 +0100 Subject: [PATCH] Cache memory buffer's name length This avoids repeated calls to strlen while we already know its value. When preprocessing sqlite3.c, this gives a surprising 2% speedup. Full benchmark available here: https://llvm-compile-time-tracker.com/compare.php?from=d14c2d408dccd8c6defa7d151e9a96be3cac8cc3&to=04f0641c1cbdcd0bdbd11cd910ca6091420bf52e&stat=instructions:u Recommit 1824432174b3166b40bce59477beb5821170748e, with restored '\0' at the end of buffer name. Differential Revision: https://reviews.llvm.org/D138555 --- llvm/lib/Support/MemoryBuffer.cpp | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/llvm/lib/Support/MemoryBuffer.cpp b/llvm/lib/Support/MemoryBuffer.cpp index 6bb046e..77c509c 100644 --- a/llvm/lib/Support/MemoryBuffer.cpp +++ b/llvm/lib/Support/MemoryBuffer.cpp @@ -77,8 +77,10 @@ void *operator new(size_t N, const NamedBufferAlloc &Alloc) { SmallString<256> NameBuf; StringRef NameRef = Alloc.Name.toStringRef(NameBuf); - char *Mem = static_cast(operator new(N + NameRef.size() + 1)); - CopyStringRef(Mem + N, NameRef); + char *Mem = static_cast(operator new(N + sizeof(size_t) + + NameRef.size() + 1)); + *reinterpret_cast(Mem + N) = NameRef.size(); + CopyStringRef(Mem + N + sizeof(size_t), NameRef); return Mem; } @@ -98,7 +100,8 @@ public: StringRef getBufferIdentifier() const override { // The name is stored after the class itself. - return StringRef(reinterpret_cast(this + 1)); + return StringRef(reinterpret_cast(this + 1) + sizeof(size_t), + *reinterpret_cast(this + 1)); } MemoryBuffer::BufferKind getBufferKind() const override { @@ -221,7 +224,8 @@ public: StringRef getBufferIdentifier() const override { // The name is stored after the class itself. - return StringRef(reinterpret_cast(this + 1)); + return StringRef(reinterpret_cast(this + 1) + sizeof(size_t), + *reinterpret_cast(this + 1)); } MemoryBuffer::BufferKind getBufferKind() const override { @@ -301,7 +305,8 @@ WritableMemoryBuffer::getNewUninitMemBuffer(size_t Size, // that MemoryBuffer and data are aligned so PointerIntPair works with them. SmallString<256> NameBuf; StringRef NameRef = BufferName.toStringRef(NameBuf); - size_t StringLen = sizeof(MemBuffer) + NameRef.size() + 1; + + size_t StringLen = sizeof(MemBuffer) + sizeof(size_t) + NameRef.size() + 1; size_t RealLen = StringLen + Size + 1 + BufAlign.value(); if (RealLen <= Size) // Check for rollover. return nullptr; @@ -310,7 +315,8 @@ WritableMemoryBuffer::getNewUninitMemBuffer(size_t Size, return nullptr; // The name is stored after the class itself. - CopyStringRef(Mem + sizeof(MemBuffer), NameRef); + *reinterpret_cast(Mem + sizeof(MemBuffer)) = NameRef.size(); + CopyStringRef(Mem + sizeof(MemBuffer) + sizeof(size_t), NameRef); // The buffer begins after the name and must be aligned. char *Buf = (char *)alignAddr(Mem + StringLen, BufAlign); -- 2.7.4