[SimpleLoopUnswitch] Fix reversed branch during condition injection

The in-loop successor is only on the left after a potential condition
inversion. As we re-use the old condition as-is, we should also
reuse the old successors as-is.

Fixes #63962.

Author: nikic

llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

@@ -3061,7 +3061,6 @@ injectPendingInvariantConditions(NonTrivialUnswitchCandidate Candidate, Loop &L,
   auto *InjectedCond =
       ICmpInst::Create(Instruction::ICmp, Pred, LHS, RHS, "injected.cond",
                        Preheader->getTerminator());
-  auto *OldCond = TI->getCondition();
 
   BasicBlock *CheckBlock = BasicBlock::Create(Ctx, BB->getName() + ".check",
                                               BB->getParent(), InLoopSucc);
@@ -3070,7 +3069,8 @@ injectPendingInvariantConditions(NonTrivialUnswitchCandidate Candidate, Loop &L,
       Builder.CreateCondBr(InjectedCond, InLoopSucc, CheckBlock);
 
   Builder.SetInsertPoint(CheckBlock);
-  auto *NewTerm = Builder.CreateCondBr(OldCond, InLoopSucc, OutOfLoopSucc);
+  auto *NewTerm = Builder.CreateCondBr(TI->getCondition(), TI->getSuccessor(0),
+                                       TI->getSuccessor(1));
 
   TI->eraseFromParent();
   // Prevent infinite unswitching.

llvm/test/Transforms/SimpleLoopUnswitch/inject-invariant-conditions.ll

@@ -465,7 +465,7 @@ define i32 @test_02_inverse(ptr noundef %p, i32 noundef %n, i32 noundef %limit,
 ; CHECK-NEXT:    br i1 [[BOUND_CHECK]], label [[GUARDED:%.*]], label [[COMMON_RET]], !prof [[PROF1]]
 ; CHECK:       guarded:
 ; CHECK-NEXT:    [[RANGE_CHECK:%.*]] = icmp uge i32 [[EL]], [[X]]
-; CHECK-NEXT:    br i1 [[RANGE_CHECK]], label [[BACKEDGE]], label [[COMMON_RET]], !llvm.invariant.condition.injection.disabled !0
+; CHECK-NEXT:    br i1 [[RANGE_CHECK]], label [[COMMON_RET]], label [[BACKEDGE]], !llvm.invariant.condition.injection.disabled !0
 ; CHECK:       backedge:
 ; CHECK-NEXT:    [[ARR_PTR:%.*]] = getelementptr i32, ptr [[ARR]], i32 [[EL]]
 ; CHECK-NEXT:    store i32 [[IV]], ptr [[ARR_PTR]], align 4