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Add implementation of BasicBlock::removePredecessor code that was factored

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out of DCE.cpp


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2001-06-29 05:25:23 +00:00
parent 25d17a5001
commit b47af25099
1 changed files with 48 additions and 0 deletions
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48
lib/VMCore/BasicBlock.cpp
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@ -11,6 +11,8 @@
#include "llvm/Method.h"
#include "llvm/SymbolTable.h"
#include "llvm/Type.h"
#include "llvm/CFG.h"
#include "llvm/iOther.h"
// Instantiate Templates - This ugliness is the price we have to pay
// for having a ValueHolderImpl.h file seperate from ValueHolder.h! :(
@ -79,6 +81,52 @@ bool BasicBlock::hasConstantPoolReferences() const {
return false;
}
// removePredecessor - This method is used to notify a BasicBlock that the
// specified Predecessor of the block is no longer able to reach it. This is
// actually not used to update the Predecessor list, but is actually used to
// update the PHI nodes that reside in the block. Note that this should be
// called while the predecessor still refers to this block.
//
void BasicBlock::removePredecessor(BasicBlock *Pred) {
using cfg::pred_begin; using cfg::pred_end; using cfg::pred_iterator;
assert(find(pred_begin(this), pred_end(this), Pred) != pred_end(this) &&
"removePredecessor: BB is not a predecessor!");
if (!front()->isPHINode()) return; // Quick exit.
pred_iterator PI(pred_begin(this)), EI(pred_end(this));
unsigned max_idx;
// Loop over the rest of the predecessors until we run out, or until we find
// out that there are more than 2 predecessors.
for (max_idx = 0; PI != EI && max_idx < 3; ++PI, ++max_idx) /*empty*/;
// If there are exactly two predecessors, then we want to nuke the PHI nodes
// altogether.
assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
if (max_idx <= 2) { // <= Two predecessors BEFORE I remove one?
while (front()->isPHINode()) { // Yup, loop through and nuke the PHI nodes
PHINode *PN = (PHINode*)front();
PN->removeIncomingValue(Pred); // Remove the predecessor first...
assert(PN->getNumIncomingValues() == max_idx-1 &&
"PHI node shouldn't have this many values!!!");
// If the PHI _HAD_ two uses, replace PHI node with its now *single* value
if (max_idx == 2)
PN->replaceAllUsesWith(PN->getOperand(0));
delete getInstList().remove(begin()); // Remove the PHI node
}
} else {
// Okay, now we know that we need to remove predecessor #pred_idx from all
// PHI nodes. Iterate over each PHI node fixing them up
iterator II(begin());
for (; (*II)->isPHINode(); ++II) {
PHINode *PN = (PHINode*)*II;
PN->removeIncomingValue(Pred);
}
}
}
// splitBasicBlock - This splits a basic block into two at the specified
// instruction. Note that all instructions BEFORE the specified iterator stay