Correctly update Changed status for SimplifyCFG

Interestingly, this leads to better output in one of the test case.

Differential Revision: https://reviews.llvm.org/D81237

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 9afc18e..23b76bd 100644 (file)
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2615,6 +2615,8 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU,
 
   const unsigned PredCount = pred_size(BB);
 
+  bool Changed = false;
+
   Instruction *Cond = nullptr;
   if (BI->isConditional())
     Cond = dyn_cast<Instruction>(BI->getCondition());
@@ -2639,16 +2641,17 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU,
             // Quit if we can't remove this instruction.
             if (!tryCSEWithPredecessor(Curr, PB))
               return false;
+            Changed = true;
           }
         }
 
     if (!Cond)
-      return false;
+      return Changed;
   }
 
   if (!Cond || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
       Cond->getParent() != BB || !Cond->hasOneUse())
-    return false;
+    return Changed;
 
   // Make sure the instruction after the condition is the cond branch.
   BasicBlock::iterator CondIt = ++Cond->getIterator();
@@ -2658,7 +2661,7 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU,
     ++CondIt;
 
   if (&*CondIt != BI)
-    return false;
+    return Changed;
 
   // Only allow this transformation if computing the condition doesn't involve
   // too many instructions and these involved instructions can be executed
@@ -2672,11 +2675,11 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU,
     if (isa<DbgInfoIntrinsic>(I))
       continue;
     if (!I->hasOneUse() || !isSafeToSpeculativelyExecute(&*I))
-      return false;
+      return Changed;
     // I has only one use and can be executed unconditionally.
     Instruction *User = dyn_cast<Instruction>(I->user_back());
     if (User == nullptr || User->getParent() != BB)
-      return false;
+      return Changed;
     // I is used in the same BB. Since BI uses Cond and doesn't have more slots
     // to use any other instruction, User must be an instruction between next(I)
     // and Cond.
@@ -2686,23 +2689,23 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU,
     NumBonusInsts += PredCount;
     // Early exits once we reach the limit.
     if (NumBonusInsts > BonusInstThreshold)
-      return false;
+      return Changed;
   }
 
   // Cond is known to be a compare or binary operator.  Check to make sure that
   // neither operand is a potentially-trapping constant expression.
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
     if (CE->canTrap())
-      return false;
+      return Changed;
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
     if (CE->canTrap())
-      return false;
+      return Changed;
 
   // Finally, don't infinitely unroll conditional loops.
   BasicBlock *TrueDest = BI->getSuccessor(0);
   BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : nullptr;
   if (TrueDest == BB || FalseDest == BB)
-    return false;
+    return Changed;
 
   for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
     BasicBlock *PredBlock = *PI;
@@ -2742,6 +2745,8 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU,
     }
 
     LLVM_DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
+    Changed = true;
+
     IRBuilder<> Builder(PBI);
 
     // If we need to invert the condition in the pred block to match, do so now.
@@ -2913,9 +2918,9 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI, MemorySSAUpdater *MSSAU,
       }
     }
 
-    return true;
+    return Changed;
   }
-  return false;
+  return Changed;
 }
 
 // If there is only one store in BB1 and BB2, return it, otherwise return

diff --git a/llvm/test/Transforms/SimplifyCFG/fold-branch-debuginvariant.ll b/llvm/test/Transforms/SimplifyCFG/fold-branch-debuginvariant.ll
index 7b26b6f..242b123 100644 (file)
--- a/llvm/test/Transforms/SimplifyCFG/fold-branch-debuginvariant.ll
+++ b/llvm/test/Transforms/SimplifyCFG/fold-branch-debuginvariant.ll
@@ -6,7 +6,6 @@
 
 ; CHECK-LABEL: bb1:
 ; CHECK: and i1 false, false
-; CHECK-LABEL: bb2:
 ; CHECK-NOT: and i1 false, false
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"