1 files changed, 18 insertions, 52 deletions

diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 711df417992b..7316db6ca02c 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -138,7 +138,7 @@ namespace {
     bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
     bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB);
   };
-}
+} // namespace
 
 char JumpThreading::ID = 0;
 INITIALIZE_PASS_BEGIN(JumpThreading, "jump-threading",
@@ -758,67 +758,33 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
 
 
   if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
-    // For a comparison where the LHS is outside this block, it's possible
-    // that we've branched on it before.  Used LVI to see if we can simplify
-    // the branch based on that.
+    // If we're branching on a conditional, LVI might be able to determine
+    // it's value at the branch instruction.  We only handle comparisons
+    // against a constant at this time.
+    // TODO: This should be extended to handle switches as well.  
     BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
     Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
-    pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
-    if (CondBr && CondConst && CondBr->isConditional() && PI != PE &&
-        (!isa<Instruction>(CondCmp->getOperand(0)) ||
-         cast<Instruction>(CondCmp->getOperand(0))->getParent() != BB)) {
-      // For predecessor edge, determine if the comparison is true or false
-      // on that edge.  If they're all true or all false, we can simplify the
-      // branch.
-      // FIXME: We could handle mixed true/false by duplicating code.
-      LazyValueInfo::Tristate Baseline =
-        LVI->getPredicateOnEdge(CondCmp->getPredicate(), CondCmp->getOperand(0),
-                                CondConst, *PI, BB, CondCmp);
-      if (Baseline != LazyValueInfo::Unknown) {
-        // Check that all remaining incoming values match the first one.
-        while (++PI != PE) {
-          LazyValueInfo::Tristate Ret =
-            LVI->getPredicateOnEdge(CondCmp->getPredicate(),
-                                    CondCmp->getOperand(0), CondConst, *PI, BB,
-                                    CondCmp);
-          if (Ret != Baseline) break;
-        }
-
-        // If we terminated early, then one of the values didn't match.
-        if (PI == PE) {
-          unsigned ToRemove = Baseline == LazyValueInfo::True ? 1 : 0;
-          unsigned ToKeep = Baseline == LazyValueInfo::True ? 0 : 1;
-          CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
-          BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
-          CondBr->eraseFromParent();
-          if (CondCmp->use_empty())
-            CondCmp->eraseFromParent();
-          else if (CondCmp->getParent() == BB) {
-            // If the fact we just learned is true for all uses of the
-            // condition, replace it with a constant value
-            auto *CI = Baseline == LazyValueInfo::True ?
-              ConstantInt::getTrue(CondCmp->getType()) :
-              ConstantInt::getFalse(CondCmp->getType());
-            CondCmp->replaceAllUsesWith(CI);
-            CondCmp->eraseFromParent();
-          }
-          return true;
-        }
-      }
-
-    } else if (CondBr && CondConst && CondBr->isConditional()) {
-      // There might be an invariant in the same block with the conditional
-      // that can determine the predicate.
-
+    if (CondBr && CondConst && CondBr->isConditional()) {
       LazyValueInfo::Tristate Ret =
         LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
-                            CondConst, CondCmp);
+                            CondConst, CondBr);
       if (Ret != LazyValueInfo::Unknown) {
         unsigned ToRemove = Ret == LazyValueInfo::True ? 1 : 0;
         unsigned ToKeep = Ret == LazyValueInfo::True ? 0 : 1;
         CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
         BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
         CondBr->eraseFromParent();
+        if (CondCmp->use_empty())
+          CondCmp->eraseFromParent();
+        else if (CondCmp->getParent() == BB) {
+          // If the fact we just learned is true for all uses of the
+          // condition, replace it with a constant value
+          auto *CI = Ret == LazyValueInfo::True ?
+            ConstantInt::getTrue(CondCmp->getType()) :
+            ConstantInt::getFalse(CondCmp->getType());
+          CondCmp->replaceAllUsesWith(CI);
+          CondCmp->eraseFromParent();
+        }
         return true;
       }
     }