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Change PHINode::hasConstantValue to have a DominatorTree argument

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instead of a bool argument, and to do the dominator check itself.
This makes it eaiser to use when DominatorTree information is
available.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80920 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2009-09-03 15:34:35 +00:00
parent dd12de686c
commit bccfc24c4e
7 changed files with 49 additions and 37 deletions
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27
lib/VMCore/Instructions.cpp
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@@ -17,6 +17,7 @@
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Operator.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/ConstantRange.h"
@@ -226,7 +227,12 @@ void PHINode::resizeOperands(unsigned NumOps) {
/// hasConstantValue - If the specified PHI node always merges together the same
/// value, return the value, otherwise return null.
///
Value *PHINode::hasConstantValue(bool AllowNonDominatingInstruction) const {
/// If the PHI has undef operands, but all the rest of the operands are
/// some unique value, return that value if it can be proved that the
/// value dominates the PHI. If DT is null, use a conservative check,
/// otherwise use DT to test for dominance.
///
Value *PHINode::hasConstantValue(DominatorTree *DT) const {
// If the PHI node only has one incoming value, eliminate the PHI node...
if (getNumIncomingValues() == 1) {
if (getIncomingValue(0) != this) // not X = phi X
@@ -260,12 +266,19 @@ Value *PHINode::hasConstantValue(bool AllowNonDominatingInstruction) const {
// instruction, we cannot always return X as the result of the PHI node. Only
// do this if X is not an instruction (thus it must dominate the PHI block),
// or if the client is prepared to deal with this possibility.
if (HasUndefInput && !AllowNonDominatingInstruction)
if (Instruction *IV = dyn_cast<Instruction>(InVal))
// If it's in the entry block, it dominates everything.
if (IV->getParent() != &IV->getParent()->getParent()->getEntryBlock() ||
isa<InvokeInst>(IV))
return 0; // Cannot guarantee that InVal dominates this PHINode.
if (HasUndefInput)
if (Instruction *IV = dyn_cast<Instruction>(InVal)) {
if (DT) {
// We have a DominatorTree. Do a precise test.
if (!DT->dominates(IV, this))
return 0;
} else {
// If it's in the entry block, it dominates everything.
if (IV->getParent() != &IV->getParent()->getParent()->getEntryBlock() ||
isa<InvokeInst>(IV))
return 0; // Cannot guarantee that InVal dominates this PHINode.
}
}
// All of the incoming values are the same, return the value now.
return InVal;