[llvm] [llvm] Improve implementation of StringRef::find_last_of and cie (PR #71865)
via llvm-commits
llvm-commits at lists.llvm.org
Thu Nov 16 08:30:05 PST 2023
https://github.com/serge-sans-paille updated https://github.com/llvm/llvm-project/pull/71865
>From 00f640e69fa819ce06000727d19db16e344b18e3 Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton at mozilla.com>
Date: Thu, 9 Nov 2023 20:41:40 +0100
Subject: [PATCH] [llvm] Improve implementation of StringRef::find_last_of for
the usual case of 2 chars
Almost all usage of StringRef::find_last_of in Clang/LLVM use a Needle
of 2 elements, which can be optimized using a generic vectorized
algorithm and a few bit hacks.
---
llvm/lib/Support/StringRef.cpp | 63 ++++++++++++++++++++++++++--------
1 file changed, 48 insertions(+), 15 deletions(-)
diff --git a/llvm/lib/Support/StringRef.cpp b/llvm/lib/Support/StringRef.cpp
index feee47ca693b251..62639feee9c084f 100644
--- a/llvm/lib/Support/StringRef.cpp
+++ b/llvm/lib/Support/StringRef.cpp
@@ -15,6 +15,7 @@
#include "llvm/Support/Error.h"
#include <bitset>
+
using namespace llvm;
// MSVC emits references to this into the translation units which reference it.
@@ -268,17 +269,47 @@ StringRef::size_type StringRef::find_first_not_of(StringRef Chars,
return npos;
}
+// See https://graphics.stanford.edu/~seander/bithacks.html#ValueInWord
+static inline uint64_t haszero(uint64_t v) {
+ return ((v)-0x0101010101010101UL) & ~(v) & 0x8080808080808080UL;
+}
+static inline uint64_t hasvalue(uint64_t x, char n) {
+ return haszero((x) ^ (~0UL / 255 * (n)));
+}
+
+/// This is a hot sport for some clangd operations, enough to be eligible to
+/// a vectorized implementation.
+static StringRef::size_type
+vectorized_find_last_of_specialized(const char *Data, size_t Sz, char C0,
+ char C1) {
+ do {
+ Sz = Sz < 8 ? 0 : Sz - 8;
+ uint64_t Buffer = 0;
+ std::memcpy((void *)&Buffer, (void *)(Data + Sz), sizeof(Buffer));
+ uint64_t Check0 = hasvalue(Buffer, C0);
+ uint64_t Check = Check0 ? Check0 : hasvalue(Buffer, C1);
+ if (Check)
+ return Sz + 7 - llvm::countl_zero(Check) / 8;
+ } while (Sz);
+ return -1;
+}
+
/// find_last_of - Find the last character in the string that is in \arg C,
/// or npos if not found.
///
/// Note: O(size() + Chars.size())
StringRef::size_type StringRef::find_last_of(StringRef Chars,
size_t From) const {
+ size_type Sz = std::min(From, Length);
+
+ if (Chars.size() == 2)
+ return vectorized_find_last_of_specialized(Data, Sz, Chars[0], Chars[1]);
+
std::bitset<1 << CHAR_BIT> CharBits;
for (char C : Chars)
CharBits.set((unsigned char)C);
- for (size_type i = std::min(From, Length) - 1, e = -1; i != e; --i)
+ for (size_type i = Sz - 1, e = -1; i != e; --i)
if (CharBits.test((unsigned char)Data[i]))
return i;
return npos;
@@ -309,9 +340,8 @@ StringRef::size_type StringRef::find_last_not_of(StringRef Chars,
return npos;
}
-void StringRef::split(SmallVectorImpl<StringRef> &A,
- StringRef Separator, int MaxSplit,
- bool KeepEmpty) const {
+void StringRef::split(SmallVectorImpl<StringRef> &A, StringRef Separator,
+ int MaxSplit, bool KeepEmpty) const {
StringRef S = *this;
// Count down from MaxSplit. When MaxSplit is -1, this will just split
@@ -372,7 +402,8 @@ size_t StringRef::count(StringRef Str) const {
size_t Count = 0;
size_t Pos = 0;
size_t N = Str.size();
- // TODO: For an empty `Str` we return 0 for legacy reasons. Consider changing
+ // TODO: For an empty `Str` we return 0 for legacy reasons. Consider
+ // changing
// this to `Length + 1` which is more in-line with the function
// description.
if (!N)
@@ -418,7 +449,8 @@ bool llvm::consumeUnsignedInteger(StringRef &Str, unsigned Radix,
Radix = GetAutoSenseRadix(Str);
// Empty strings (after the radix autosense) are invalid.
- if (Str.empty()) return true;
+ if (Str.empty())
+ return true;
// Parse all the bytes of the string given this radix. Watch for overflow.
StringRef Str2 = Str;
@@ -504,8 +536,8 @@ bool llvm::getAsSignedInteger(StringRef Str, unsigned Radix,
if (consumeSignedInteger(Str, Radix, Result))
return true;
- // For getAsSignedInteger, we require the whole string to be consumed or else
- // we consider it a failure.
+ // For getAsSignedInteger, we require the whole string to be consumed or
+ // else we consider it a failure.
return !Str.empty();
}
@@ -519,7 +551,8 @@ bool StringRef::consumeInteger(unsigned Radix, APInt &Result) {
assert(Radix > 1 && Radix <= 36);
// Empty strings (after the radix autosense) are invalid.
- if (Str.empty()) return true;
+ if (Str.empty())
+ return true;
// Skip leading zeroes. This can be a significant improvement if
// it means we don't need > 64 bits.
@@ -535,7 +568,8 @@ bool StringRef::consumeInteger(unsigned Radix, APInt &Result) {
// (Over-)estimate the required number of bits.
unsigned Log2Radix = 0;
- while ((1U << Log2Radix) < Radix) Log2Radix++;
+ while ((1U << Log2Radix) < Radix)
+ Log2Radix++;
bool IsPowerOf2Radix = ((1U << Log2Radix) == Radix);
unsigned BitWidth = Log2Radix * Str.size();
@@ -556,11 +590,11 @@ bool StringRef::consumeInteger(unsigned Radix, APInt &Result) {
while (!Str.empty()) {
unsigned CharVal;
if (Str[0] >= '0' && Str[0] <= '9')
- CharVal = Str[0]-'0';
+ CharVal = Str[0] - '0';
else if (Str[0] >= 'a' && Str[0] <= 'z')
- CharVal = Str[0]-'a'+10;
+ CharVal = Str[0] - 'a' + 10;
else if (Str[0] >= 'A' && Str[0] <= 'Z')
- CharVal = Str[0]-'A'+10;
+ CharVal = Str[0] - 'A' + 10;
else
break;
@@ -623,8 +657,7 @@ hash_code llvm::hash_value(StringRef S) {
}
unsigned DenseMapInfo<StringRef, void>::getHashValue(StringRef Val) {
- assert(Val.data() != getEmptyKey().data() &&
- "Cannot hash the empty key!");
+ assert(Val.data() != getEmptyKey().data() && "Cannot hash the empty key!");
assert(Val.data() != getTombstoneKey().data() &&
"Cannot hash the tombstone key!");
return (unsigned)(hash_value(Val));
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