[ValueTracking] Improve isImpliedCondition for conditions with matching operands.

This patch improves SimplifyCFG to catch cases like:

  if (a < b) {
    if (a > b) <- known to be false
      unreachable;
  }

Phabricator Revision: http://reviews.llvm.org/D18905

llvm-svn: 266767

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 2def0b5..d68dd14 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -928,9 +928,10 @@ bool JumpThreading::ProcessImpliedCondition(BasicBlock *BB) {
     if (!PBI || !PBI->isConditional() || PBI->getSuccessor(0) != CurrentBB)
       return false;
 
-    if (isImpliedCondition(PBI->getCondition(), Cond, DL)) {
-      BI->getSuccessor(1)->removePredecessor(BB);
-      BranchInst::Create(BI->getSuccessor(0), BI);
+    bool ImpliedTrue;
+    if (isImpliedCondition(PBI->getCondition(), Cond, ImpliedTrue, DL)) {
+      BI->getSuccessor(ImpliedTrue ? 1 : 0)->removePredecessor(BB);
+      BranchInst::Create(BI->getSuccessor(ImpliedTrue ? 0 : 1), BI);
       BI->eraseFromParent();
       return true;
     }