From b3d59701c89a6e03a0e0909543f3e7bd9140900f Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Thu, 7 Jul 2005 20:40:38 +0000 Subject: [PATCH] Fix a problem that instcombine would hit when dealing with unreachable code. Because the instcombine has to scan the entire function when it starts up to begin with, we might as well do it in DFO so we can nuke unreachable code. This fixes: Transforms/InstCombine/2005-07-07-DeadPHILoop.ll git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22348 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../Scalar/InstructionCombining.cpp | 34 ++++++++++++++++--- 1 file changed, 29 insertions(+), 5 deletions(-) diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 55dd09846e6..e2ef04ea1df 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -45,9 +45,9 @@ #include "llvm/Support/CallSite.h" #include "llvm/Support/Debug.h" #include "llvm/Support/GetElementPtrTypeIterator.h" -#include "llvm/Support/InstIterator.h" #include "llvm/Support/InstVisitor.h" #include "llvm/Support/PatternMatch.h" +#include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/Statistic.h" #include "llvm/ADT/STLExtras.h" #include @@ -4400,7 +4400,8 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) { // However, because we don't have dom info, we can't do a perfect job. if (Instruction *I = dyn_cast(V)) { // We know that the instruction dominates the PHI if there are no undef - // values coming in. + // values coming in. If the instruction is defined in the entry block, + // and is not an invoke, we know it is ok. if (I->getParent() != &I->getParent()->getParent()->front() || isa(I)) for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) @@ -5226,9 +5227,32 @@ bool InstCombiner::runOnFunction(Function &F) { bool Changed = false; TD = &getAnalysis(); - for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) - WorkList.push_back(&*i); - + { + // Populate the worklist with the reachable instructions. + std::set Visited; + for (df_ext_iterator BB = df_ext_begin(&F.front(), Visited), + E = df_ext_end(&F.front(), Visited); BB != E; ++BB) + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) + WorkList.push_back(I); + + // Do a quick scan over the function. If we find any blocks that are + // unreachable, remove any instructions inside of them. This prevents + // the instcombine code from having to deal with some bad special cases. + for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) + if (!Visited.count(BB)) { + Instruction *Term = BB->getTerminator(); + while (Term != BB->begin()) { // Remove instrs bottom-up + BasicBlock::iterator I = Term; --I; + + DEBUG(std::cerr << "IC: DCE: " << *I); + ++NumDeadInst; + + if (!I->use_empty()) + I->replaceAllUsesWith(UndefValue::get(I->getType())); + I->eraseFromParent(); + } + } + } while (!WorkList.empty()) { Instruction *I = WorkList.back(); // Get an instruction from the worklist -- 2.34.1