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More isel time load folding checking for nodes that produce flag values. 

See comment in CanBeFoldedBy() for detailed explanation.

llvm-svn: 30851
This commit is contained in:
Evan Cheng 2006-10-10 01:46:56 +00:00
parent e01ee43cdc
commit 61b8b43bbe
1 changed files with 57 additions and 6 deletions
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63
llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
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@ -213,7 +213,20 @@ namespace {
};
}
static void findNonImmUse(SDNode* Use, SDNode* Def, bool &found,
static SDNode *findFlagUse(SDNode *N) {
unsigned FlagResNo = N->getNumValues()-1;
for (SDNode::use_iterator I = N->use_begin(), E = N->use_end(); I != E; ++I) {
SDNode *User = *I;
for (unsigned i = 0, e = User->getNumOperands(); i != e; ++i) {
SDOperand Op = User->getOperand(i);
if (Op.ResNo == FlagResNo)
return User;
}
}
return NULL;
}
static void findNonImmUse(SDNode* Use, SDNode* Def, SDNode *Ignore, bool &found,
std::set<SDNode *> &Visited) {
if (found ||
Use->getNodeId() > Def->getNodeId() ||
@ -222,8 +235,10 @@ static void findNonImmUse(SDNode* Use, SDNode* Def, bool &found,
for (unsigned i = 0, e = Use->getNumOperands(); i != e; ++i) {
SDNode *N = Use->getOperand(i).Val;
if (N == Ignore)
continue;
if (N != Def) {
findNonImmUse(N, Def, found, Visited);
findNonImmUse(N, Def, Ignore, found, Visited);
} else {
found = true;
break;
@ -231,16 +246,27 @@ static void findNonImmUse(SDNode* Use, SDNode* Def, bool &found,
}
}
static inline bool isNonImmUse(SDNode* Use, SDNode* Def) {
static inline bool isNonImmUse(SDNode* Use, SDNode* Def, SDNode *Ignore=NULL) {
std::set<SDNode *> Visited;
bool found = false;
for (unsigned i = 0, e = Use->getNumOperands(); i != e; ++i) {
SDNode *N = Use->getOperand(i).Val;
if (N != Def) {
findNonImmUse(N, Def, found, Visited);
if (N != Def && N != Ignore) {
findNonImmUse(N, Def, Ignore, found, Visited);
if (found) break;
}
}
if (!found && Ignore) {
// We must be checking for reachability between Def and a flag use. Go down
// recursively if Use also produces a flag.
MVT::ValueType VT = Use->getValueType(Use->getNumValues()-1);
if (VT == MVT::Flag && !Use->use_empty()) {
SDNode *FU = findFlagUse(Use);
if (FU)
return !isNonImmUse(FU, Def, Use);
}
}
return found;
}
@ -258,7 +284,32 @@ bool X86DAGToDAGISel::CanBeFoldedBy(SDNode *N, SDNode *U) {
// / [X]
// | ^
// [U]--------|
return !FastISel && !isNonImmUse(U, N);
if (!FastISel && !isNonImmUse(U, N)) {
// If U produces a flag, then it gets (even more) interesting. Since it
// would have been "glued" together with its flag use, we need to check if
// it might reach N:
//
// [ N ]
// ^ ^
// | |
// [U] \--
// ^ [TF]
// | |
// \ /
// [FU]
//
// If FU (flag use) indirectly reach N (the load), and U fold N (call it
// NU), then TF is a predecessor of FU and a successor of NU. But since
// NU and FU are flagged together, this effectively creates a cycle.
MVT::ValueType VT = U->getValueType(U->getNumValues()-1);
if (VT == MVT::Flag && !U->use_empty()) {
SDNode *FU = findFlagUse(U);
if (FU)
return !isNonImmUse(FU, N, U);
}
return true;
}
return false;
}
/// MoveBelowTokenFactor - Replace TokenFactor operand with load's chain operand