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Tweak hash function and compress hash tables.

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Make the hash tables as small as possible while ensuring that all
lookups can be done in less than 8 probes.

Cut the aliases hash table in half by only storing a < b pairs - it
is a symmetric relation.

Use larger multipliers on the initial hash function to ensure that it
properly covers the whole table, and to resolve some clustering in the
very regular ARM register bank.

This reduces the size of most of these tables by 4x - 8x. For instance,
the ARM tables shrink from 48 KB to 8 KB.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132888 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2011-06-12 07:04:32 +00:00
parent bf710cc23e
commit b95fd2d5fd
2 changed files with 34 additions and 28 deletions
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21
include/llvm/Target/TargetRegisterInfo.h
View File

@ -471,19 +471,21 @@ public:
if (regA == regB)
return true;
if (regA > regB)
std::swap(regA, regB);
if (isVirtualRegister(regA) || isVirtualRegister(regB))
return false;
// regA and regB are distinct physical registers. Do they alias?
size_t index = (regA + regB * 37) & (AliasesHashSize-1);
unsigned ProbeAmt = 0;
while (AliasesHash[index*2] != 0 &&
AliasesHash[index*2+1] != 0) {
size_t index = (regA * 11 + regB * 97) & (AliasesHashSize-1);
unsigned ProbeAmt = 1;
while (AliasesHash[index*2] != 0 && AliasesHash[index*2+1] != 0) {
if (AliasesHash[index*2] == regA && AliasesHash[index*2+1] == regB)
return true;
index = (index + ProbeAmt) & (AliasesHashSize-1);
ProbeAmt += 2;
ProbeAmt += 1;
}
return false;
@ -493,15 +495,14 @@ public:
///
bool isSubRegister(unsigned regA, unsigned regB) const {
// SubregHash is a simple quadratically probed hash table.
size_t index = (regA + regB * 37) & (SubregHashSize-1);
unsigned ProbeAmt = 2;
while (SubregHash[index*2] != 0 &&
SubregHash[index*2+1] != 0) {
size_t index = (regA * 11 + regB * 97) & (SubregHashSize-1);
unsigned ProbeAmt = 1;
while (SubregHash[index*2] != 0 && SubregHash[index*2+1] != 0) {
if (SubregHash[index*2] == regA && SubregHash[index*2+1] == regB)
return true;
index = (index + ProbeAmt) & (SubregHashSize-1);
ProbeAmt += 2;
ProbeAmt += 1;
}
return false;

41
utils/TableGen/RegisterInfoEmitter.cpp
View File

@ -137,27 +137,31 @@ static void generateHashTable(raw_ostream &OS, const char *Name,
unsigned HSize = Data.size();
UUVector HT;
// Hashtable size must be a power of two.
HSize = 2 * NextPowerOf2(2 * HSize);
HT.assign(HSize, Sentinel);
// Grow the hash table until all entries can be found in less than 8 probes.
unsigned MaxProbes;
do {
// Hashtable size must be a power of two.
HSize = NextPowerOf2(HSize);
HT.assign(HSize, Sentinel);
// Insert all entries.
unsigned MaxProbes = 0;
for (unsigned i = 0, e = Data.size(); i != e; ++i) {
UUPair D = Data[i];
unsigned Idx = (D.first + D.second * 37) & (HSize - 1);
unsigned ProbeAmt = 2;
while (HT[Idx] != Sentinel) {
Idx = (Idx + ProbeAmt) & (HSize - 1);
ProbeAmt += 2;
// Insert all entries.
MaxProbes = 0;
for (unsigned i = 0, e = Data.size(); i != e; ++i) {
UUPair D = Data[i];
unsigned Idx = (D.first * 11 + D.second * 97) & (HSize - 1);
unsigned ProbeAmt = 1;
while (HT[Idx] != Sentinel) {
Idx = (Idx + ProbeAmt) & (HSize - 1);
ProbeAmt += 1;
}
HT[Idx] = D;
MaxProbes = std::max(MaxProbes, ProbeAmt);
}
HT[Idx] = D;
MaxProbes = std::max(MaxProbes, ProbeAmt/2);
}
OS << "\n // Max number of probes: " << MaxProbes;
} while (MaxProbes >= 8);
// Print the hash table.
OS << "\n\n // Max number of probes: " << MaxProbes
<< "\n // Used entries: " << Data.size()
OS << "\n // Used entries: " << Data.size()
<< "\n const unsigned " << Name << "Size = " << HSize << ';'
<< "\n const unsigned " << Name << "[] = {\n";
@ -441,13 +445,14 @@ void RegisterInfoEmitter::run(raw_ostream &OS) {
// Print the AliasHashTable, a simple quadratically probed
// hash table for determining if a register aliases another register.
// Since the overlaps() relation is symmetric, only store a < b pairs.
HTData.clear();
for (unsigned i = 0, e = Regs.size(); i != e; ++i) {
unsigned RegNo = Regs[i].EnumValue;
const CodeGenRegister::Set &O = Overlaps[&Regs[i]];
for (CodeGenRegister::Set::const_iterator I = O.begin(), E = O.end();
I != E; ++I)
if (*I != &Regs[i])
if (RegNo < (*I)->EnumValue)
HTData.push_back(UUPair(RegNo, (*I)->EnumValue));
}
generateHashTable(OS, "AliasesHashTable", HTData);