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move some generally useful functions out of jump threading

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into libanalysis and transformutils.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86735 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2009-11-10 22:26:15 +00:00
parent 5b37fbac1a
commit 40d8c28b27
5 changed files with 106 additions and 85 deletions
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83
lib/Transforms/Scalar/JumpThreading.cpp
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@@ -203,89 +203,6 @@ static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) {
return Size;
}
//===----------------------------------------------------------------------===//
/// ReplaceAndSimplifyAllUses - Perform From->replaceAllUsesWith(To) and then
/// delete the From instruction. In addition to a basic RAUW, this does a
/// recursive simplification of the newly formed instructions. This catches
/// things where one simplification exposes other opportunities. This only
/// simplifies and deletes scalar operations, it does not change the CFG.
///
static void ReplaceAndSimplifyAllUses(Instruction *From, Value *To,
const TargetData *TD) {
assert(From != To && "ReplaceAndSimplifyAllUses(X,X) is not valid!");
// FromHandle - This keeps a weakvh on the from value so that we can know if
// it gets deleted out from under us in a recursive simplification.
WeakVH FromHandle(From);
while (!From->use_empty()) {
// Update the instruction to use the new value.
Use &U = From->use_begin().getUse();
Instruction *User = cast<Instruction>(U.getUser());
U = To;
// See if we can simplify it.
if (Value *V = SimplifyInstruction(User, TD)) {
// Recursively simplify this.
ReplaceAndSimplifyAllUses(User, V, TD);
// If the recursive simplification ended up revisiting and deleting 'From'
// then we're done.
if (FromHandle == 0)
return;
}
}
From->eraseFromParent();
}
/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
/// method is called when we're about to delete Pred as a predecessor of BB. If
/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
///
/// Unlike the removePredecessor method, this attempts to simplify uses of PHI
/// nodes that collapse into identity values. For example, if we have:
/// x = phi(1, 0, 0, 0)
/// y = and x, z
///
/// .. and delete the predecessor corresponding to the '1', this will attempt to
/// recursively fold the and to 0.
static void RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
TargetData *TD) {
// This only adjusts blocks with PHI nodes.
if (!isa<PHINode>(BB->begin()))
return;
// Remove the entries for Pred from the PHI nodes in BB, but do not simplify
// them down. This will leave us with single entry phi nodes and other phis
// that can be removed.
BB->removePredecessor(Pred, true);
WeakVH PhiIt = &BB->front();
while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
Value *PNV = PN->hasConstantValue();
if (PNV == 0) continue;
// If we're able to simplify the phi to a single value, substitute the new
// value into all of its uses.
assert(PNV != PN && "hasConstantValue broken");
ReplaceAndSimplifyAllUses(PN, PNV, TD);
// If recursive simplification ended up deleting the next PHI node we would
// iterate to, then our iterator is invalid, restart scanning from the top
// of the block.
if (PhiIt == 0) PhiIt = &BB->front();
}
}
//===----------------------------------------------------------------------===//
/// FindLoopHeaders - We do not want jump threading to turn proper loop
/// structures into irreducible loops. Doing this breaks up the loop nesting
/// hierarchy and pessimizes later transformations. To prevent this from