Implement SimplifyCFG/DeadSetCC.ll

SimplifyCFG is one of those passes that we use for final cleanup: it should
not rely on other passes to clean up its garbage.  This fixes the "why are
trivially dead setcc's in the output of gccas" problem.

llvm-svn: 19212

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index bbeb28d9772..f4d02573cdc 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -521,8 +521,16 @@ static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
       SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PTI);
       for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
         NewSI->addCase(PredCases[i].first, PredCases[i].second);
+
+      Instruction *DeadCond = 0;
+      if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
+        // If PTI is a branch, remember the condition.
+        DeadCond = dyn_cast<Instruction>(BI->getCondition());
       Pred->getInstList().erase(PTI);
 
+      // If the condition is dead now, remove the instruction tree.
+      if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond);
+
       // Okay, last check.  If BB is still a successor of PSI, then we must
       // have an infinite loop case.  If so, add an infinitely looping block
       // to handle the case to preserve the behavior of the code.