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Tolerate pathological growth of optCSEHash #40056

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merged 4 commits into from
Jul 29, 2020
Merged

Tolerate pathological growth of optCSEHash #40056

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2cc3091
growing hash
davidwrighton Jul 28, 2020
9c68487
Use bucket size metric and fix typos
davidwrighton Jul 29, 2020
79c37e7
Fix formatting and build issues
davidwrighton Jul 29, 2020
804fdd7
Fix formatting and comments
davidwrighton Jul 29, 2020
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7 changes: 6 additions & 1 deletion src/coreclr/src/jit/compiler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -6363,7 +6363,12 @@ class Compiler
// not used for shared const CSE's
};

static const size_t s_optCSEhashSize;
static const size_t s_optCSEhashSizeInitial;
static const size_t s_optCSEhashGrowthFactor;
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This could be renamed to indicate that it is the initial hash table size

s_optCSEhashSize => s_optCSEhashSizeInitial

static const size_t s_optCSEhashBucketSize;
size_t optCSEhashSize; // The current size of hashtable
size_t optCSEhashCount; // Number of entries in hashtable
size_t optCSEhashMaxCountBeforeResize; // Number of entries before resize
CSEdsc** optCSEhash;
CSEdsc** optCSEtab;

Expand Down
69 changes: 56 additions & 13 deletions src/coreclr/src/jit/optcse.cpp
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Expand Up @@ -20,7 +20,9 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
/*****************************************************************************/

/* static */
const size_t Compiler::s_optCSEhashSize = EXPSET_SZ * 2;
const size_t Compiler::s_optCSEhashSizeInitial = EXPSET_SZ * 2;
const size_t Compiler::s_optCSEhashGrowthFactor = 2;
const size_t Compiler::s_optCSEhashBucketSize = 4;

/*****************************************************************************
*
Expand All @@ -36,11 +38,11 @@ void Compiler::optCSEstop()

CSEdsc* dsc;
CSEdsc** ptr;
unsigned cnt;
size_t cnt;

optCSEtab = new (this, CMK_CSE) CSEdsc*[optCSECandidateCount]();

for (cnt = s_optCSEhashSize, ptr = optCSEhash; cnt; cnt--, ptr++)
for (cnt = optCSEhashSize, ptr = optCSEhash; cnt; cnt--, ptr++)
{
for (dsc = *ptr; dsc; dsc = dsc->csdNextInBucket)
{
Expand Down Expand Up @@ -373,7 +375,11 @@ void Compiler::optValnumCSE_Init()
cseMaskTraits = nullptr;

// Allocate and clear the hash bucket table
optCSEhash = new (this, CMK_CSE) CSEdsc*[s_optCSEhashSize]();
optCSEhash = new (this, CMK_CSE) CSEdsc*[s_optCSEhashSizeInitial]();

optCSEhashSize = s_optCSEhashSizeInitial;
optCSEhashMaxCountBeforeResize = optCSEhashSize * s_optCSEhashBucketSize;
optCSEhashCount = 0;

optCSECandidateCount = 0;
optDoCSE = false; // Stays false until we find duplicate CSE tree
Expand All @@ -382,6 +388,20 @@ void Compiler::optValnumCSE_Init()
optCseCheckedBoundMap = nullptr;
}

unsigned optCSEKeyToHashIndex(size_t key, size_t optCSEhashSize)
{
unsigned hash;

hash = (unsigned)key;
#ifdef TARGET_64BIT
hash ^= (unsigned)(key >> 32);
#endif
hash *= (unsigned)(optCSEhashSize + 1);
hash >>= 7;

return hash % optCSEhashSize;
}

//---------------------------------------------------------------------------
// optValnumCSE_Index:
// - Returns the CSE index to use for this tree,
Expand All @@ -402,7 +422,6 @@ void Compiler::optValnumCSE_Init()
unsigned Compiler::optValnumCSE_Index(GenTree* tree, Statement* stmt)
{
size_t key;
unsigned hash;
unsigned hval;
CSEdsc* hashDsc;
bool isIntConstHash = false;
Expand Down Expand Up @@ -502,14 +521,7 @@ unsigned Compiler::optValnumCSE_Index(GenTree* tree, Statement* stmt)

// Compute the hash value for the expression

hash = (unsigned)key;
#ifdef TARGET_64BIT
hash ^= (unsigned)(key >> 32);
#endif
hash *= (unsigned)(s_optCSEhashSize + 1);
hash >>= 7;

hval = hash % s_optCSEhashSize;
hval = optCSEKeyToHashIndex(key, optCSEhashSize);

/* Look for a matching index in the hash table */

Expand Down Expand Up @@ -627,6 +639,37 @@ unsigned Compiler::optValnumCSE_Index(GenTree* tree, Statement* stmt)

if (optCSECandidateCount < MAX_CSE_CNT)
{
if (optCSEhashCount == optCSEhashMaxCountBeforeResize)
{
size_t newOptCSEhashSize = optCSEhashSize * s_optCSEhashGrowthFactor;
CSEdsc** newOptCSEhash = new (this, CMK_CSE) CSEdsc*[newOptCSEhashSize]();

// Iterate through each existing entry, moving to the new table
CSEdsc** ptr;
CSEdsc* dsc;
size_t cnt;
for (cnt = optCSEhashSize, ptr = optCSEhash; cnt; cnt--, ptr++)
{
for (dsc = *ptr; dsc;)
{
CSEdsc* nextDsc = dsc->csdNextInBucket;

size_t newHval = optCSEKeyToHashIndex(dsc->csdHashKey, newOptCSEhashSize);

// Move CSEdsc to bucket in enlarged table
dsc->csdNextInBucket = newOptCSEhash[newHval];
newOptCSEhash[newHval] = dsc;

dsc = nextDsc;
}
}

optCSEhash = newOptCSEhash;
optCSEhashSize = newOptCSEhashSize;
optCSEhashMaxCountBeforeResize = optCSEhashMaxCountBeforeResize * s_optCSEhashGrowthFactor;
}

++optCSEhashCount;
hashDsc = new (this, CMK_CSE) CSEdsc;

hashDsc->csdHashKey = key;
Expand Down