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Turn store -> null/undef into the LLVM unreachable instruction! This simple

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change hacks off 10K of bytecode from perlbmk (.5%) even though the front-end
is not generating them yet and we are not optimizing the resultant code.
This isn't too bad.

llvm-svn: 17111
This commit is contained in:
Chris Lattner 2004-10-18 03:00:50 +00:00
parent 18333c64de
commit 3c1be63b41
1 changed files with 27 additions and 0 deletions
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27
lib/Transforms/Scalar/SimplifyCFG.cpp
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@ -20,6 +20,8 @@
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Support/CFG.h"
#include "llvm/Pass.h"
@ -45,6 +47,31 @@ static bool MarkAliveBlocks(BasicBlock *BB, std::set<BasicBlock*> &Reachable) {
if (Reachable.count(BB)) return false;
Reachable.insert(BB);
// Do a quick scan of the basic block, turning any obviously unreachable
// instructions into LLVM unreachable insts. The instruction combining pass
// canonnicalizes unreachable insts into stores to null or undef.
for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ++BBI)
if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
if (isa<ConstantPointerNull>(SI->getOperand(1)) ||
isa<UndefValue>(SI->getOperand(1))) {
// Loop over all of the successors, removing BB's entry from any PHI
// nodes.
for (succ_iterator I = succ_begin(BB), SE = succ_end(BB); I != SE; ++I)
(*I)->removePredecessor(BB);
new UnreachableInst(SI);
std::cerr << "Inserted UNREACHABLE instruction!\n";
// All instructions after this are dead.
for (; BBI != E; ) {
if (!BBI->use_empty())
BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
BB->getInstList().erase(BBI++);
}
break;
}
bool Changed = ConstantFoldTerminator(BB);
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
MarkAliveBlocks(*SI, Reachable);