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Implement a new RemoveSuccessor function

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3131 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2002-07-29 22:32:08 +00:00
parent 229a3770f6
commit b0f0ef8f26
1 changed files with 51 additions and 4 deletions
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55
lib/Transforms/Utils/BasicBlockUtils.cpp
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@ -7,7 +7,9 @@
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Function.h"
#include "llvm/Instruction.h"
#include "llvm/iTerminators.h"
#include "llvm/Constant.h"
#include "llvm/Type.h"
#include <algorithm>
// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
@ -50,11 +52,56 @@ void ReplaceInstWithInst(BasicBlock::InstListType &BIL,
}
// ReplaceInstWithInst - Replace the instruction specified by From with the
// instruction specified by To. Note that this is slower than providing an
// iterator directly, because the basic block containing From must be searched
// for the instruction.
// instruction specified by To.
//
void ReplaceInstWithInst(Instruction *From, Instruction *To) {
BasicBlock::iterator BI(From);
ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
}
// RemoveSuccessor - Change the specified terminator instruction such that its
// successor #SuccNum no longer exists. Because this reduces the outgoing
// degree of the current basic block, the actual terminator instruction itself
// may have to be changed. In the case where the last successor of the block is
// deleted, a return instruction is inserted in its place which can cause a
// suprising change in program behavior if it is not expected.
//
void RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) {
assert(SuccNum < TI->getNumSuccessors() &&
"Trying to remove a nonexistant successor!");
// If our old successor block contains any PHI nodes, remove the entry in the
// PHI nodes that comes from this branch...
//
BasicBlock *BB = TI->getParent();
TI->getSuccessor(SuccNum)->removePredecessor(BB);
TerminatorInst *NewTI = 0;
switch (TI->getOpcode()) {
case Instruction::Br:
// If this is a conditional branch... convert to unconditional branch.
if (TI->getNumSuccessors() == 2) {
cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum));
} else { // Otherwise convert to a return instruction...
Value *RetVal = 0;
// Create a value to return... if the function doesn't return null...
if (BB->getParent()->getReturnType() != Type::VoidTy)
RetVal = Constant::getNullValue(BB->getParent()->getReturnType());
// Create the return...
NewTI = new ReturnInst(RetVal);
}
break;
case Instruction::Invoke: // Should convert to call
case Instruction::Switch: // Should remove entry
default:
case Instruction::Ret: // Cannot happen, has no successors!
assert(0 && "Unhandled terminator instruction type in RemoveSuccessor!");
abort();
}
if (NewTI) // If it's a different instruction, replace.
ReplaceInstWithInst(TI, NewTI);
}