[llvm] r247253 - [ADT] Apply a large hammer to StringRef functions: attribute always_inline.
Justin Bogner via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 16 12:53:01 PDT 2015
Chandler Carruth <chandlerc at gmail.com> writes:
> Sure, I hadn't realized how much this hurt debugging for you. How can we
> fix it? We're in violent agreement that this is a total workaround that we
> should do if there is a low cost way, not something we should jsut do
> blindly.
The case that's been coming up for me is basically just the "char *"
constructor - calling functions with a "char *" and getting the
conversion is pretty common while debugging. It seems like a reasonable
trade off to leave the attribute on the non-constructor methods, which
mostly just access attributes you can get at in the debugger anyway, and
just drop it for the constructors. WDYT?
> On Tue, Sep 15, 2015 at 8:16 PM Justin Bogner <mail at justinbogner.com> wrote:
>
>> Chandler Carruth via llvm-commits <llvm-commits at lists.llvm.org> writes:
>> > Author: chandlerc
>> > Date: Thu Sep 10 03:29:35 2015
>> > New Revision: 247253
>> >
>> > URL: http://llvm.org/viewvc/llvm-project?rev=247253&view=rev
>> > Log:
>> > [ADT] Apply a large hammer to StringRef functions: attribute
>> always_inline.
>> >
>> > The logic of this follows something Howard does in libc++ and something
>> > I discussed with Chris eons ago -- for a lot of functions, there is
>> > really no benefit to preserving "debug information" by leaving the
>> > out-of-line even in debug builds. This is especially true as we now do
>> > a very good job of preserving most debug information even in the face of
>> > inlining. There are a bunch of methods in StringRef that we are paying
>> > a completely unacceptable amount for with every debug build of every
>> > LLVM developer.
>> >
>> > Some day, we should fix Clang/LLVM so that developers can reasonable
>> > use a default of something other than '-O0' and not waste their lives
>> > waiting on *completely* unoptimized code to execute. We should have
>> > a default that doesn't impede debugging while providing at least
>> > plausable performance.
>> >
>> > But today is not that day.
>> >
>> > So today, I'm applying always_inline to the functions that are really
>> > hurting the critical path for stuff like 'check_llvm'. I'm being very
>> > cautious here, but there are a few other APIs that we really should do
>> > this for as a matter of pragmatism. Hopefully we can rip this out some
>> > day.
>> >
>> > With this change, TripleTest.Normalization runtime decreases by over
>> > 10%, and the total 'check-llvm' time on my 48-core box goes from 38s to
>> > just under 37s.
>> >
>> > Modified:
>> > llvm/trunk/include/llvm/ADT/StringRef.h
>> >
>> > Modified: llvm/trunk/include/llvm/ADT/StringRef.h
>> > URL:
>> >
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/StringRef.h?rev=247253&r1=247252&r2=247253&view=diff
>> >
>> ==============================================================================
>> >
>> > --- llvm/trunk/include/llvm/ADT/StringRef.h (original)
>> > +++ llvm/trunk/include/llvm/ADT/StringRef.h Thu Sep 10 03:29:35 2015
>> > @@ -10,6 +10,7 @@
>> > #ifndef LLVM_ADT_STRINGREF_H
>> > #define LLVM_ADT_STRINGREF_H
>> >
>> > +#include "llvm/Support/Compiler.h"
>> > #include <algorithm>
>> > #include <cassert>
>> > #include <cstring>
>> > @@ -53,6 +54,7 @@ namespace llvm {
>> >
>> > // Workaround memcmp issue with null pointers (undefined behavior)
>> > // by providing a specialized version
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > static int compareMemory(const char *Lhs, const char *Rhs, size_t
>> Length) {
>> > if (Length == 0) { return 0; }
>> > return ::memcmp(Lhs,Rhs,Length);
>> > @@ -63,9 +65,11 @@ namespace llvm {
>> > /// @{
>> >
>>
>> > /// Construct an empty string ref.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > /*implicit*/ StringRef() : Data(nullptr), Length(0) {}
>> >
>> > /// Construct a string ref from a cstring.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > /*implicit*/ StringRef(const char *Str)
>> > : Data(Str) {
>> > assert(Str && "StringRef cannot be built from a NULL argument");
>> > @@ -73,6 +77,7 @@ namespace llvm {
>> > }
>> >
>> > /// Construct a string ref from a pointer and length.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > /*implicit*/ StringRef(const char *data, size_t length)
>> > : Data(data), Length(length) {
>> > assert((data || length == 0) &&
>> > @@ -80,6 +85,7 @@ namespace llvm {
>> > }
>> >
>> > /// Construct a string ref from an std::string.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > /*implicit*/ StringRef(const std::string &Str)
>> > : Data(Str.data()), Length(Str.length()) {}
>>
>> This makes constructing StringRefs in lldb basically impossible, which
>> means that functions in llvm that take a string for an argument are
>> basically uncallable in a debugger. So, basically, this makes my life
>> much worse. I'm fine with making "-O0 -g" builds faster if there isn't
>> really a cost to it, but this kind of thing is just a work around for
>> the fact that nobody's bothering to invest in making optimized debugging
>> in llvm useable. The trade off is wrong.
>>
>> >
>> > @@ -104,12 +110,15 @@ namespace llvm {
>> >
>> > /// data - Get a pointer to the start of the string (which may not
>> be null
>> > /// terminated).
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > const char *data() const { return Data; }
>> >
>> > /// empty - Check if the string is empty.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > bool empty() const { return Length == 0; }
>> >
>> > /// size - Get the string size.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > size_t size() const { return Length; }
>> >
>> > /// front - Get the first character in the string.
>> > @@ -133,6 +142,7 @@ namespace llvm {
>> >
>> > /// equals - Check for string equality, this is more efficient than
>> > /// compare() when the relative ordering of inequal strings isn't
>> needed.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > bool equals(StringRef RHS) const {
>> > return (Length == RHS.Length &&
>> > compareMemory(Data, RHS.Data, RHS.Length) == 0);
>> > @@ -145,6 +155,7 @@ namespace llvm {
>> >
>> > /// compare - Compare two strings; the result is -1, 0, or 1 if
>> this string
>> > /// is lexicographically less than, equal to, or greater than the
>> \p RHS.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > int compare(StringRef RHS) const {
>> > // Check the prefix for a mismatch.
>> > if (int Res = compareMemory(Data, RHS.Data, std::min(Length,
>> RHS.Length)))
>> > @@ -212,6 +223,7 @@ namespace llvm {
>> > /// @{
>> >
>> > /// Check if this string starts with the given \p Prefix.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > bool startswith(StringRef Prefix) const {
>> > return Length >= Prefix.Length &&
>> > compareMemory(Data, Prefix.Data, Prefix.Length) == 0;
>> > @@ -221,6 +233,7 @@ namespace llvm {
>> > bool startswith_lower(StringRef Prefix) const;
>> >
>> > /// Check if this string ends with the given \p Suffix.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > bool endswith(StringRef Suffix) const {
>> > return Length >= Suffix.Length &&
>> > compareMemory(end() - Suffix.Length, Suffix.Data,
>> Suffix.Length) == 0;
>> > @@ -237,6 +250,7 @@ namespace llvm {
>> > ///
>> > /// \returns The index of the first occurrence of \p C, or npos if
>> not
>> > /// found.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > size_t find(char C, size_t From = 0) const {
>> > size_t FindBegin = std::min(From, Length);
>> > if (FindBegin < Length) { // Avoid calling memchr with nullptr.
>> > @@ -402,6 +416,7 @@ namespace llvm {
>> > /// \param N The number of characters to included in the substring.
>> If N
>> > /// exceeds the number of characters remaining in the string, the
>> string
>> > /// suffix (starting with \p Start) will be returned.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > StringRef substr(size_t Start, size_t N = npos) const {
>> > Start = std::min(Start, Length);
>> > return StringRef(Data + Start, std::min(N, Length - Start));
>> > @@ -409,6 +424,7 @@ namespace llvm {
>> >
>> > /// Return a StringRef equal to 'this' but with the first \p N
>> elements
>> > /// dropped.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > StringRef drop_front(size_t N = 1) const {
>> > assert(size() >= N && "Dropping more elements than exist");
>> > return substr(N);
>> > @@ -416,6 +432,7 @@ namespace llvm {
>> >
>> > /// Return a StringRef equal to 'this' but with the last \p N
>> elements
>> > /// dropped.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > StringRef drop_back(size_t N = 1) const {
>> > assert(size() >= N && "Dropping more elements than exist");
>> > return substr(0, size()-N);
>> > @@ -431,6 +448,7 @@ namespace llvm {
>> > /// substring. If this is npos, or less than \p Start, or exceeds
>> the
>> > /// number of characters remaining in the string, the string suffix
>> > /// (starting with \p Start) will be returned.
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > StringRef slice(size_t Start, size_t End) const {
>> > Start = std::min(Start, Length);
>> > End = std::min(std::max(Start, End), Length);
>> > @@ -547,10 +565,12 @@ namespace llvm {
>> > /// @name StringRef Comparison Operators
>> > /// @{
>> >
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > inline bool operator==(StringRef LHS, StringRef RHS) {
>> > return LHS.equals(RHS);
>> > }
>> >
>> > + LLVM_ATTRIBUTE_ALWAYS_INLINE
>> > inline bool operator!=(StringRef LHS, StringRef RHS) {
>> > return !(LHS == RHS);
>> > }
>> >
>> >
>> > _______________________________________________
>> > llvm-commits mailing list
>> > llvm-commits at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>>
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