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TLI: Microoptimize calls to strlen+memcmp to strncmp. 

The strlen+memcmp was hidden in a call to StringRef::operator==. We check if
there are any null bytes in the string upfront so we can simplify the comparison
Small speedup when compiling code with many function calls.

llvm-svn: 176766
This commit is contained in:
Benjamin Kramer 2013-03-09 13:48:23 +00:00
parent 2ef36b633b
commit 160f72dc8e
1 changed files with 24 additions and 2 deletions
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26
llvm/lib/Target/TargetLibraryInfo.cpp
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@ -597,15 +597,37 @@ TargetLibraryInfo::TargetLibraryInfo(const TargetLibraryInfo &TLI)
CustomNames = TLI.CustomNames;
}
namespace {
struct StringComparator {
/// Compare two strings and return true if LHS is lexicographically less than
/// RHS. Requires that RHS doesn't contain any zero bytes.
bool operator()(const char *LHS, StringRef RHS) const {
// Compare prefixes with strncmp. If prefixes match we know that LHS is
// greater or equal to RHS as RHS can't contain any '\0'.
return std::strncmp(LHS, RHS.data(), RHS.size()) < 0;
}
// Provided for compatibility with MSVC's debug mode.
bool operator()(StringRef LHS, const char *RHS) const { return LHS < RHS; }
bool operator()(StringRef LHS, StringRef RHS) const { return LHS < RHS; }
};
}
bool TargetLibraryInfo::getLibFunc(StringRef funcName,
LibFunc::Func &F) const {
const char **Start = &StandardNames[0];
const char **End = &StandardNames[LibFunc::NumLibFuncs];
// Filter out empty names and names containing null bytes, those can't be in
// our table.
if (funcName.empty() || funcName.find('\0') != StringRef::npos)
return false;
// Check for \01 prefix that is used to mangle __asm declarations and
// strip it if present.
if (!funcName.empty() && funcName.front() == '\01')
if (funcName.front() == '\01')
funcName = funcName.substr(1);
const char **I = std::lower_bound(Start, End, funcName);
const char **I = std::lower_bound(Start, End, funcName, StringComparator());
if (I != End && *I == funcName) {
F = (LibFunc::Func)(I - Start);
return true;