From 011de07117dbc0b49d80f6f254dcf26b71c22e09 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Mon, 29 Jul 2002 22:31:39 +0000 Subject: [PATCH] Fix bug: test/Regression/Transforms/ADCE/2002-07-29-Segfault.ll git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3129 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/ADCE.cpp | 88 +++++++++++++++++++++++----------- 1 file changed, 60 insertions(+), 28 deletions(-) diff --git a/lib/Transforms/Scalar/ADCE.cpp b/lib/Transforms/Scalar/ADCE.cpp index 06301971f73..bba30a123a1 100644 --- a/lib/Transforms/Scalar/ADCE.cpp +++ b/lib/Transforms/Scalar/ADCE.cpp @@ -8,6 +8,7 @@ #include "llvm/Transforms/Scalar.h" #include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/Type.h" #include "llvm/Analysis/Dominators.h" #include "llvm/iTerminators.h" @@ -209,41 +210,72 @@ bool ADCE::doADCE() { BasicBlock *BB = I; TerminatorInst *TI = BB->getTerminator(); - // Loop over all of the successors, looking for ones that are not alive - for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) + // Loop over all of the successors, looking for ones that are not alive. + // We cannot save the number of successors in the terminator instruction + // here because we may remove them if we don't have a postdominator... + // + for (unsigned i = 0; i != TI->getNumSuccessors(); ++i) if (!AliveBlocks.count(TI->getSuccessor(i))) { // Scan up the postdominator tree, looking for the first // postdominator that is alive, and the last postdominator that is // dead... // PostDominatorTree::Node *LastNode = DT[TI->getSuccessor(i)]; - PostDominatorTree::Node *NextNode = LastNode->getIDom(); - while (!AliveBlocks.count(NextNode->getNode())) { - LastNode = NextNode; - NextNode = NextNode->getIDom(); - } - - // Get the basic blocks that we need... - BasicBlock *LastDead = LastNode->getNode(); - BasicBlock *NextAlive = NextNode->getNode(); - - // Make the conditional branch now go to the next alive block... - TI->getSuccessor(i)->removePredecessor(BB); - TI->setSuccessor(i, NextAlive); - - // If there are PHI nodes in NextAlive, we need to add entries to - // the PHI nodes for the new incoming edge. The incoming values - // should be identical to the incoming values for LastDead. + + // There is a special case here... if there IS no post-dominator for + // the block we have no owhere to point our branch to. Instead, + // convert it to a return. This can only happen if the code + // branched into an infinite loop. Note that this may not be + // desirable, because we _are_ altering the behavior of the code. + // This is a well known drawback of ADCE, so in the future if we + // choose to revisit the decision, this is where it should be. // - for (BasicBlock::iterator II = NextAlive->begin(); - PHINode *PN = dyn_cast(&*II); ++II) { - // Get the incoming value for LastDead... - int OldIdx = PN->getBasicBlockIndex(LastDead); - assert(OldIdx != -1 && "LastDead is not a pred of NextAlive!"); - Value *InVal = PN->getIncomingValue(OldIdx); - - // Add an incoming value for BB now... - PN->addIncoming(InVal, BB); + if (LastNode == 0) { // No postdominator! + // Call RemoveSuccessor to transmogrify the terminator instruction + // to not contain the outgoing branch, or to create a new + // terminator if the form fundementally changes (ie unconditional + // branch to return). Note that this will change a branch into an + // infinite loop into a return instruction! + // + RemoveSuccessor(TI, i); + + // RemoveSuccessor may replace TI... make sure we have a fresh + // pointer... and e variable. + // + TI = BB->getTerminator(); + + // Rescan this successor... + --i; + } else { + PostDominatorTree::Node *NextNode = LastNode->getIDom(); + + while (!AliveBlocks.count(NextNode->getNode())) { + LastNode = NextNode; + NextNode = NextNode->getIDom(); + } + + // Get the basic blocks that we need... + BasicBlock *LastDead = LastNode->getNode(); + BasicBlock *NextAlive = NextNode->getNode(); + + // Make the conditional branch now go to the next alive block... + TI->getSuccessor(i)->removePredecessor(BB); + TI->setSuccessor(i, NextAlive); + + // If there are PHI nodes in NextAlive, we need to add entries to + // the PHI nodes for the new incoming edge. The incoming values + // should be identical to the incoming values for LastDead. + // + for (BasicBlock::iterator II = NextAlive->begin(); + PHINode *PN = dyn_cast(&*II); ++II) { + // Get the incoming value for LastDead... + int OldIdx = PN->getBasicBlockIndex(LastDead); + assert(OldIdx != -1 && "LastDead is not a pred of NextAlive!"); + Value *InVal = PN->getIncomingValue(OldIdx); + + // Add an incoming value for BB now... + PN->addIncoming(InVal, BB); + } } } -- 2.34.1