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Simplify and generalize X86DAGToDAGISel::CanBeFoldedBy, and draw

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up some new ascii art to illustrate what it does. This change
currently has no effect on generated code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56270 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2008-09-17 01:39:10 +00:00
parent d3ead4329e
commit 682d5a8834
1 changed files with 49 additions and 57 deletions
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106
lib/Target/X86/X86ISelDAGToDAG.cpp
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@ -268,7 +268,7 @@ static SDNode *findFlagUse(SDNode *N) {
/// non-immediate use of "Def". This function recursively traversing
/// up the operand chain ignoring certain nodes.
static void findNonImmUse(SDNode *Use, SDNode* Def, SDNode *ImmedUse,
SDNode *Root, SDNode *Skip, bool &found,
SDNode *Root, bool &found,
SmallPtrSet<SDNode*, 16> &Visited) {
if (found ||
Use->getNodeId() > Def->getNodeId() ||
@ -277,26 +277,16 @@ static void findNonImmUse(SDNode *Use, SDNode* Def, SDNode *ImmedUse,
for (unsigned i = 0, e = Use->getNumOperands(); !found && i != e; ++i) {
SDNode *N = Use->getOperand(i).getNode();
if (N == Skip)
continue;
if (N == Def) {
if (Use == ImmedUse)
if (Use == ImmedUse || Use == Root)
continue; // We are not looking for immediate use.
if (Use == Root) {
// Must be a chain reading node where it is possible to reach its own
// chain operand through a path started from another operand.
assert(Use->getOpcode() == ISD::STORE ||
Use->getOpcode() == X86ISD::CMP ||
Use->getOpcode() == ISD::INTRINSIC_W_CHAIN ||
Use->getOpcode() == ISD::INTRINSIC_VOID);
continue;
}
assert(N != Root);
found = true;
break;
}
// Traverse up the operand chain.
findNonImmUse(N, Def, ImmedUse, Root, Skip, found, Visited);
findNonImmUse(N, Def, ImmedUse, Root, found, Visited);
}
}
@ -309,11 +299,10 @@ static void findNonImmUse(SDNode *Use, SDNode* Def, SDNode *ImmedUse,
/// have one non-chain use, we only need to watch out for load/op/store
/// and load/op/cmp case where the root (store / cmp) may reach the load via
/// its chain operand.
static inline bool isNonImmUse(SDNode *Root, SDNode *Def, SDNode *ImmedUse,
SDNode *Skip = NULL) {
static inline bool isNonImmUse(SDNode *Root, SDNode *Def, SDNode *ImmedUse) {
SmallPtrSet<SDNode*, 16> Visited;
bool found = false;
findNonImmUse(Root, Def, ImmedUse, Root, Skip, found, Visited);
findNonImmUse(Root, Def, ImmedUse, Root, found, Visited);
return found;
}
@ -321,55 +310,58 @@ static inline bool isNonImmUse(SDNode *Root, SDNode *Def, SDNode *ImmedUse,
bool X86DAGToDAGISel::CanBeFoldedBy(SDNode *N, SDNode *U, SDNode *Root) const {
if (Fast) return false;
// If U use can somehow reach N through another path then U can't fold N or
// it will create a cycle. e.g. In the following diagram, U can reach N
// through X. If N is folded into into U, then X is both a predecessor and
// a successor of U.
// If Root use can somehow reach N through a path that that doesn't contain
// U then folding N would create a cycle. e.g. In the following
// diagram, Root can reach N through X. If N is folded into into Root, then
// X is both a predecessor and a successor of U.
//
// [ N ]
// ^ ^
// | |
// / \---
// / [X]
// | ^
// [U]--------|
// [N*] //
// ^ ^ //
// / \ //
// [U*] [X]? //
// ^ ^ //
// \ / //
// \ / //
// [Root*] //
//
// * indicates nodes to be folded together.
//
// If Root produces a flag, then it gets (even more) interesting. Since it
// will be "glued" together with its flag use in the scheduler, we need to
// check if it might reach N.
//
// [N*] //
// ^ ^ //
// / \ //
// [U*] [X]? //
// ^ ^ //
// \ \ //
// \ | //
// [Root*] | //
// ^ | //
// f | //
// | / //
// [Y] / //
// ^ / //
// f / //
// | / //
// [FU] //
//
// If FU (flag use) indirectly reaches N (the load), and Root folds N
// (call it Fold), then X is a predecessor of FU and a successor of
// Fold. But since Fold and FU are flagged together, this will create
// a cycle in the scheduling graph.
if (isNonImmUse(Root, N, U))
return false;
// 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.
bool HasFlagUse = false;
MVT VT = Root->getValueType(Root->getNumValues()-1);
while ((VT == MVT::Flag && !Root->use_empty())) {
while (VT == MVT::Flag) {
SDNode *FU = findFlagUse(Root);
if (FU == NULL)
break;
else {
Root = FU;
HasFlagUse = true;
}
Root = FU;
VT = Root->getValueType(Root->getNumValues()-1);
}
if (HasFlagUse)
return !isNonImmUse(Root, N, Root, U);
return true;
return !isNonImmUse(Root, N, U);
}
/// MoveBelowTokenFactor - Replace TokenFactor operand with load's chain operand