[SimplifyCFG] Cleanup redundant conditions [NFC].

Summary:
Since the for loop iterates over BB's predecessors, the branch conditions found must have BB as one of the successors.
For an unconditional branch the successor must be BB, added `assert`.
For a conditional branch, one of the two successors must be BB, simplify `else if` to `else` and `assert`.
Sink common instructions outside the if/else block.

Reviewers: sanjoy.google

Subscribers: jlebar, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65596

llvm-svn: 367699

1 files changed, 8 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 2c433cb0277..63015e69a36 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4178,24 +4178,22 @@ bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
     IRBuilder<> Builder(TI);
     if (auto *BI = dyn_cast<BranchInst>(TI)) {
       if (BI->isUnconditional()) {
-        if (BI->getSuccessor(0) == BB) {
-          new UnreachableInst(TI->getContext(), TI);
-          TI->eraseFromParent();
-          Changed = true;
-        }
+        assert(BI->getSuccessor(0) == BB && "Incorrect CFG");
+        new UnreachableInst(TI->getContext(), TI);
+        TI->eraseFromParent();
+        Changed = true;
       } else {
         Value* Cond = BI->getCondition();
         if (BI->getSuccessor(0) == BB) {
           Builder.CreateAssumption(Builder.CreateNot(Cond));
           Builder.CreateBr(BI->getSuccessor(1));
-          EraseTerminatorAndDCECond(BI);
-          Changed = true;
-        } else if (BI->getSuccessor(1) == BB) {
+        } else {
+          assert(BI->getSuccessor(1) == BB && "Incorrect CFG");
           Builder.CreateAssumption(Cond);
           Builder.CreateBr(BI->getSuccessor(0));
-          EraseTerminatorAndDCECond(BI);
-          Changed = true;
         }
+        EraseTerminatorAndDCECond(BI);
+        Changed = true;
       }
     } else if (auto *SI = dyn_cast<SwitchInst>(TI)) {
       SwitchInstProfUpdateWrapper SU(*SI);