Improve performance of constructing filesystem::path from strings.
This patch fixes a performance bug when constructing or appending to a path
from a string or c-string. Previously we called 'push_back' to append every
single character. This caused multiple re-allocation and copies when at most
one reallocation is necessary. The new behavior is to simply call
`string::append` so it can correctly handle reallocation.
For large strings this change is a ~4x improvement. This also makes our path
faster to construct than libstdc++'s.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@285530 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/experimental/filesystem/path.cpp b/src/experimental/filesystem/path.cpp
index be970a8..546f3c4 100644
--- a/src/experimental/filesystem/path.cpp
+++ b/src/experimental/filesystem/path.cpp
@@ -42,8 +42,7 @@
public:
PathParser(string_view_t P, string_view_t E, unsigned char S)
: Path(P), RawEntry(E), State(static_cast<ParserState>(S)) {
- assert(S != 0);
- assert(S != PS_BeforeBegin);
+ // S cannot be '0' or PS_BeforeBegin.
}
static PathParser CreateBegin(string_view_t P) noexcept {
@@ -94,7 +93,6 @@
case PS_InFilenames: {
PosPtr SepEnd = consumeSeparator(Start, End);
- assert(SepEnd);
if (SepEnd != End) {
PosPtr TkEnd = consumeName(SepEnd, End);
if (TkEnd)
@@ -131,7 +129,6 @@
SepEnd + 1, RStart + 1);
} else {
PosPtr TkStart = consumeName(RStart, REnd);
- assert(TkStart);
if (TkStart == REnd + 2 && consumeSeparator(TkStart, REnd) == REnd)
return makeState(PS_InRootName, Path.data(), RStart + 1);
else
@@ -192,14 +189,10 @@
private:
void makeState(ParserState NewState, PosPtr Start, PosPtr End) noexcept {
- assert(NewState != PS_BeforeBegin && NewState != PS_AtEnd);
State = NewState;
- assert(Start < End);
- assert(Start >= &Path.front() && End <= &Path.back() + 1);
RawEntry = string_view_t(Start, End - Start);
}
void makeState(ParserState NewState) noexcept {
- assert(NewState == PS_BeforeBegin || NewState == PS_AtEnd);
State = NewState;
RawEntry = {};
}