/**************************************************************************************
*
* Corresponding to the live definition pushes, pop the stack as we finish a sub-paths
* of the graph originating from the block. Refer SSA renaming for any additional info.
* "curSsaName" tracks the currently live definitions.
*/
void Compiler::optBlockCopyPropPopStacks(BasicBlock* block, LclNumToGenTreePtrStack* curSsaName)
{
for (GenTreePtr stmt = block->bbTreeList; stmt; stmt = stmt->gtNext)
{
for (GenTreePtr tree = stmt->gtStmt.gtStmtList; tree; tree = tree->gtNext)
{
if (!tree->IsLocal())
{
continue;
}
unsigned lclNum = tree->gtLclVarCommon.gtLclNum;
if (fgExcludeFromSsa(lclNum))
{
continue;
}
if (tree->gtFlags & GTF_VAR_DEF)
{
GenTreePtrStack* stack = nullptr;
curSsaName->Lookup(lclNum, &stack);
stack->Pop();
if (stack->Height() == 0)
{
curSsaName->Remove(lclNum);
}
}
}
}
}
/**************************************************************************************
*
* Perform copy propagation on a given tree as we walk the graph and if it is a local
* variable, then look up all currently live definitions and check if any of those
* definitions share the same value number. If so, then we can make the replacement.
*
*/
void Compiler::optCopyProp(BasicBlock* block, GenTreePtr stmt, GenTreePtr tree, LclNumToGenTreePtrStack* curSsaName)
{
// TODO-Review: EH successor/predecessor iteration seems broken.
if (block->bbCatchTyp == BBCT_FINALLY || block->bbCatchTyp == BBCT_FAULT)
{
return;
}
// If not local nothing to do.
if (!tree->IsLocal())
{
return;
}
if (tree->OperGet() == GT_PHI_ARG || tree->OperGet() == GT_LCL_FLD)
{
return;
}
// Propagate only on uses.
if (tree->gtFlags & GTF_VAR_DEF)
{
return;
}
unsigned lclNum = tree->AsLclVarCommon()->GetLclNum();
// Skip address exposed variables.
if (fgExcludeFromSsa(lclNum))
{
return;
}
assert(tree->gtVNPair.GetConservative() != ValueNumStore::NoVN);
for (LclNumToGenTreePtrStack::KeyIterator iter = curSsaName->Begin(); !iter.Equal(curSsaName->End()); ++iter)
{
unsigned newLclNum = iter.Get();
GenTreePtr op = iter.GetValue()->Index(0);
// Nothing to do if same.
if (lclNum == newLclNum)
{
continue;
}
// Skip variables with assignments embedded in the statement (i.e., with a comma). Because we
// are not currently updating their SSA names as live in the copy-prop pass of the stmt.
if (VarSetOps::IsMember(this, optCopyPropKillSet, lvaTable[newLclNum].lvVarIndex))
{
continue;
}
if (op->gtFlags & GTF_VAR_CAST)
{
continue;
}
if (gsShadowVarInfo != nullptr && lvaTable[newLclNum].lvIsParam &&
gsShadowVarInfo[newLclNum].shadowCopy == lclNum)
{
continue;
}
ValueNum opVN = GetUseAsgDefVNOrTreeVN(op);
if (opVN == ValueNumStore::NoVN)
{
continue;
}
if (op->TypeGet() != tree->TypeGet())
{
continue;
}
if (opVN != tree->gtVNPair.GetConservative())
{
continue;
}
if (optCopyProp_LclVarScore(&lvaTable[lclNum], &lvaTable[newLclNum], true) <= 0)
{
continue;
}
// Check whether the newLclNum is live before being substituted. Otherwise, we could end
// up in a situation where there must've been a phi node that got pruned because the variable
// is not live anymore. For example,
// if
// x0 = 1
// else
// x1 = 2
// print(c) <-- x is not live here. Let's say 'c' shares the value number with "x0."
//
// If we simply substituted 'c' with "x0", we would be wrong. Ideally, there would be a phi
// node x2 = phi(x0, x1) which can then be used to substitute 'c' with. But because of pruning
// there would be no such phi node. To solve this we'll check if 'x' is live, before replacing
// 'c' with 'x.'
if (!lvaTable[newLclNum].lvVerTypeInfo.IsThisPtr())
{
if (lvaTable[newLclNum].lvAddrExposed)
{
continue;
}
// We compute liveness only on tracked variables. So skip untracked locals.
if (!lvaTable[newLclNum].lvTracked)
{
continue;
}
// Because of this dependence on live variable analysis, CopyProp phase is immediately
// after Liveness, SSA and VN.
if (!VarSetOps::IsMember(this, compCurLife, lvaTable[newLclNum].lvVarIndex))
{
continue;
}
}
unsigned newSsaNum = SsaConfig::RESERVED_SSA_NUM;
if (op->gtFlags & GTF_VAR_DEF)
{
newSsaNum = GetSsaNumForLocalVarDef(op);
}
else // parameters, this pointer etc.
{
newSsaNum = op->AsLclVarCommon()->GetSsaNum();
}
if (newSsaNum == SsaConfig::RESERVED_SSA_NUM)
{
continue;
}
#ifdef DEBUG
if (verbose)
{
JITDUMP("VN based copy assertion for ");
printTreeID(tree);
printf(" V%02d @%08X by ", lclNum, tree->GetVN(VNK_Conservative));
printTreeID(op);
printf(" V%02d @%08X.\n", newLclNum, op->GetVN(VNK_Conservative));
gtDispTree(tree, nullptr, nullptr, true);
}
#endif
lvaTable[lclNum].decRefCnts(block->getBBWeight(this), this);
lvaTable[newLclNum].incRefCnts(block->getBBWeight(this), this);
tree->gtLclVarCommon.SetLclNum(newLclNum);
tree->AsLclVarCommon()->SetSsaNum(newSsaNum);
#ifdef DEBUG
if (verbose)
{
printf("copy propagated to:\n");
gtDispTree(tree, nullptr, nullptr, true);
}
#endif
break;
}
return;
}
/**************************************************************************************
*
* Helper to check if tree is a local that participates in SSA numbering.
*/
bool Compiler::optIsSsaLocal(GenTreePtr tree)
{
return tree->IsLocal() && !fgExcludeFromSsa(tree->AsLclVarCommon()->GetLclNum());
}
bool RangeCheck::IsMonotonicallyIncreasing(GenTreePtr expr, SearchPath* path)
{
JITDUMP("[RangeCheck::IsMonotonicallyIncreasing] %p\n", dspPtr(expr));
if (path->Lookup(expr))
{
return true;
}
// Add hashtable entry for expr.
path->Set(expr, NULL);
// Remove hashtable entry for expr when we exit the present scope.
auto code = [&] { path->Remove(expr); };
jitstd::utility::scoped_code<decltype(code)> finally(code);
// If the rhs expr is constant, then it is not part of the dependency
// loop which has to increase monotonically.
ValueNum vn = expr->gtVNPair.GetConservative();
if (m_pCompiler->vnStore->IsVNConstant(vn))
{
return true;
}
// If the rhs expr is local, then try to find the def of the local.
else if (expr->IsLocal())
{
Location* loc = GetDef(expr);
if (loc == nullptr)
{
return false;
}
GenTreePtr asg = loc->parent;
assert(asg->OperKind() & GTK_ASGOP);
switch (asg->OperGet())
{
case GT_ASG:
return IsMonotonicallyIncreasing(asg->gtGetOp2(), path);
case GT_ASG_ADD:
return IsBinOpMonotonicallyIncreasing(asg->gtGetOp1(), asg->gtGetOp2(), GT_ADD, path);
}
JITDUMP("Unknown local definition type\n");
return false;
}
else if (expr->OperGet() == GT_ADD)
{
return IsBinOpMonotonicallyIncreasing(expr->gtGetOp1(), expr->gtGetOp2(), GT_ADD, path);
}
else if (expr->OperGet() == GT_PHI)
{
for (GenTreeArgList* args = expr->gtOp.gtOp1->AsArgList();
args != nullptr; args = args->Rest())
{
// If the arg is already in the path, skip.
if (path->Lookup(args->Current()))
{
continue;
}
if (!IsMonotonicallyIncreasing(args->Current(), path))
{
JITDUMP("Phi argument not monotonic\n");
return false;
}
}
return true;
}
JITDUMP("Unknown tree type\n");
return false;
}