[llvm-commits] CVS: llvm/lib/Transforms/Scalar/ADCE.cpp
Chris Lattner
lattner at cs.uiuc.edu
Tue Jun 24 18:03:01 PDT 2003
Changes in directory llvm/lib/Transforms/Scalar:
ADCE.cpp updated: 1.55 -> 1.56
---
Log message:
Fix bug: ADCE/2003-06-24-BadSuccessor.ll
---
Diffs of the changes:
Index: llvm/lib/Transforms/Scalar/ADCE.cpp
diff -u llvm/lib/Transforms/Scalar/ADCE.cpp:1.55 llvm/lib/Transforms/Scalar/ADCE.cpp:1.56
--- llvm/lib/Transforms/Scalar/ADCE.cpp:1.55 Tue Jun 24 16:49:45 2003
+++ llvm/lib/Transforms/Scalar/ADCE.cpp Tue Jun 24 18:02:45 2003
@@ -73,6 +73,8 @@
// instructions that are dead according to LiveSet.
bool dropReferencesOfDeadInstructionsInLiveBlock(BasicBlock *BB);
+ TerminatorInst *convertToUnconditionalBranch(TerminatorInst *TI);
+
inline void markInstructionLive(Instruction *I) {
if (LiveSet.count(I)) return;
DEBUG(std::cerr << "Insn Live: " << I);
@@ -139,6 +141,24 @@
}
+/// convertToUnconditionalBranch - Transform this conditional terminator
+/// instruction into an unconditional branch because we don't care which of the
+/// successors it goes to. This eliminate a use of the condition as well.
+///
+TerminatorInst *ADCE::convertToUnconditionalBranch(TerminatorInst *TI) {
+ BranchInst *NB = new BranchInst(TI->getSuccessor(0), TI);
+ BasicBlock *BB = TI->getParent();
+
+ // Remove entries from PHI nodes to avoid confusing ourself later...
+ for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
+ TI->getSuccessor(i)->removePredecessor(BB);
+
+ // Delete the old branch itself...
+ BB->getInstList().erase(TI);
+ return NB;
+}
+
+
// doADCE() - Run the Aggressive Dead Code Elimination algorithm, returning
// true if the function was modified.
//
@@ -234,13 +254,25 @@
// new entry node...
//
if (AliveBlocks.size() == Func->size()) { // No dead blocks?
- for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I)
+ for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I) {
// Loop over all of the instructions in the function, telling dead
// instructions to drop their references. This is so that the next sweep
// over the program can safely delete dead instructions without other dead
// instructions still refering to them.
//
dropReferencesOfDeadInstructionsInLiveBlock(I);
+
+ // Check to make sure the terminator instruction is live. If it isn't,
+ // this means that the condition that it branches on (we know it is not an
+ // unconditional branch), is not needed to make the decision of where to
+ // go to, because all outgoing edges go to the same place. We must remove
+ // the use of the condition (because it's probably dead), so we convert
+ // the terminator to a conditional branch.
+ //
+ TerminatorInst *TI = I->getTerminator();
+ if (!LiveSet.count(TI))
+ convertToUnconditionalBranch(TI);
+ }
} else { // If there are some blocks dead...
// If the entry node is dead, insert a new entry node to eliminate the entry
@@ -269,17 +301,8 @@
// on a condition that doesn't matter. Make it an unconditional branch
// to ONE of the successors. This has the side effect of dropping a use
// of the conditional value, which may also be dead.
- if (!LiveSet.count(TI)) {
- assert(TI->getNumSuccessors() > 1 && "Not a conditional?");
- BranchInst *NB = new BranchInst(TI->getSuccessor(0), TI);
-
- // Remove entries from PHI nodes to avoid confusing ourself later...
- for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
- TI->getSuccessor(i)->removePredecessor(BB);
-
- BB->getInstList().erase(TI);
- TI = NB;
- }
+ if (!LiveSet.count(TI))
+ TI = convertToUnconditionalBranch(TI);
// Loop over all of the successors, looking for ones that are not alive.
// We cannot save the number of successors in the terminator instruction
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