Revert "[BDCE][DemandedBits] Detect dead uses of undead instructions"
This reverts commit r349674. It causes a failure in
test-suite enc-3des.execution_time.
llvm-svn: 349684
diff --git a/llvm/lib/Transforms/Scalar/BDCE.cpp b/llvm/lib/Transforms/Scalar/BDCE.cpp
index 65a68c1..f63182e 100644
--- a/llvm/lib/Transforms/Scalar/BDCE.cpp
+++ b/llvm/lib/Transforms/Scalar/BDCE.cpp
@@ -96,38 +96,30 @@
if (I.mayHaveSideEffects() && I.use_empty())
continue;
- // Remove instructions not reached during analysis.
- if (DB.isInstructionDead(&I)) {
- salvageDebugInfo(I);
- Worklist.push_back(&I);
- I.dropAllReferences();
- Changed = true;
- continue;
- }
-
- for (Use &U : I.operands()) {
- // DemandedBits only detects dead integer uses.
- if (!U->getType()->isIntOrIntVectorTy())
- continue;
-
- // TODO: We could also find dead non-instruction uses, e.g. arguments.
- if (!isa<Instruction>(U))
- continue;
-
- if (!DB.isUseDead(&U))
- continue;
-
- LLVM_DEBUG(dbgs() << "BDCE: Trivializing: " << U << " (all bits dead)\n");
+ if (I.getType()->isIntOrIntVectorTy() &&
+ !DB.getDemandedBits(&I).getBoolValue()) {
+ // For live instructions that have all dead bits, first make them dead by
+ // replacing all uses with something else. Then, if they don't need to
+ // remain live (because they have side effects, etc.) we can remove them.
+ LLVM_DEBUG(dbgs() << "BDCE: Trivializing: " << I << " (all bits dead)\n");
clearAssumptionsOfUsers(&I, DB);
// FIXME: In theory we could substitute undef here instead of zero.
// This should be reconsidered once we settle on the semantics of
// undef, poison, etc.
- U.set(ConstantInt::get(U->getType(), 0));
+ Value *Zero = ConstantInt::get(I.getType(), 0);
++NumSimplified;
+ I.replaceNonMetadataUsesWith(Zero);
Changed = true;
}
+ if (!DB.isInstructionDead(&I))
+ continue;
+
+ salvageDebugInfo(I);
+ Worklist.push_back(&I);
+ I.dropAllReferences();
+ Changed = true;
}
for (Instruction *&I : Worklist) {