[SimplifyCFG] Fix a debug invariant bug in FoldBranchToCommonDest()

Summary:
Fix a case where FoldBranchToCommonDest() would bail out from doing CSE
when encountering a debug intrinsic. Handle that by skipping past the
debug intrinsics.

Also, as a minor refactoring, rename checkCSEInPredecessor() to
tryCSEWithPredecessor() to make it a bit more clear that the function
may remove instructions.

Reviewers: fhahn, craig.topper, dblaikie, xbolva00

Reviewed By: fhahn, xbolva00

Subscribers: vsk, davide, llvm-commits

Differential Revision: https://reviews.llvm.org/D46635

llvm-svn: 332698

1 files changed, 5 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 833e13f890d..c38164e6bd1 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2498,7 +2498,7 @@ static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
 
 /// Return true if the given instruction is available
 /// in its predecessor block. If yes, the instruction will be removed.
-static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
+static bool tryCSEWithPredecessor(Instruction *Inst, BasicBlock *PB) {
   if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
     return false;
   for (Instruction &I : *PB) {
@@ -2555,14 +2555,16 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, unsigned BonusInstThreshold) {
         if (PBI->isConditional() &&
             (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
              BI->getSuccessor(0) == PBI->getSuccessor(1))) {
-          for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
+          for (auto I = BB->instructionsWithoutDebug().begin(),
+                    E = BB->instructionsWithoutDebug().end();
+               I != E;) {
             Instruction *Curr = &*I++;
             if (isa<CmpInst>(Curr)) {
               Cond = Curr;
               break;
             }
             // Quit if we can't remove this instruction.
-            if (!checkCSEInPredecessor(Curr, PB))
+            if (!tryCSEWithPredecessor(Curr, PB))
               return false;
           }
         }