[SimplifyCFG] Handle trunc condition in foldBranchToCommonDest.

Author: andjo403

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -4087,9 +4087,7 @@ bool llvm::foldBranchToCommonDest(BranchInst *BI, DomTreeUpdater *DTU,
 
   Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
 
-  if (!Cond ||
-      (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond) &&
-       !isa<SelectInst>(Cond)) ||
+  if (!Cond || !isa<CmpInst, BinaryOperator, SelectInst, TruncInst>(Cond) ||
       Cond->getParent() != BB || !Cond->hasOneUse())
     return false;
 

llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll

@@ -88,10 +88,9 @@ define void @one_pred_trunc_cond(i8 %v0, i8 %v1) {
 ; CHECK-LABEL: @one_pred_trunc_cond(
 ; CHECK-NEXT:  pred:
 ; CHECK-NEXT:    [[C0:%.*]] = icmp eq i8 [[V0:%.*]], 0
-; CHECK-NEXT:    br i1 [[C0]], label [[DISPATCH:%.*]], label [[FINAL_RIGHT:%.*]]
-; CHECK:       dispatch:
 ; CHECK-NEXT:    [[C1:%.*]] = trunc i8 [[V1:%.*]] to i1
-; CHECK-NEXT:    br i1 [[C1]], label [[FINAL_LEFT:%.*]], label [[FINAL_RIGHT]]
+; CHECK-NEXT:    [[OR_COND:%.*]] = select i1 [[C0]], i1 [[C1]], i1 false
+; CHECK-NEXT:    br i1 [[OR_COND]], label [[FINAL_LEFT:%.*]], label [[FINAL_RIGHT:%.*]]
 ; CHECK:       common.ret:
 ; CHECK-NEXT:    ret void
 ; CHECK:       final_left: