[LoopSimplifyCFG] Fix inconsistency in blocks in loop markup

[mkazantsev]

Summary

2nd part of D57095 with the same reason, just in another place. We never
fold branches that are not immediately in the current loop, but this check
is missing in IsEdgeLive As result, it may think that the edge in subloop is
dead while it's live. It's a pessimization in the current stance.

lib/Transforms/Scalar/LoopSimplifyCFG.cpp

for (auto *ExitBlock : ExitBlocks)
         DeadExitBlocks.push_back(ExitBlock);
 
     // Whether or not the edge From->To will still be present in graph after the
     // folding.
     auto IsEdgeLive = [&](BasicBlock *From, BasicBlock *To) {
       if (!LiveLoopBlocks.count(From))
         return false;
       BasicBlock *TheOnlySucc = getOnlyLiveSuccessor(From);
-      return !TheOnlySucc || TheOnlySucc == To;
+      return !TheOnlySucc || TheOnlySucc == To || LI.getLoopFor(From) != &L;
     };
 
     // The loop will not be destroyed if its latch is live.
     DeleteCurrentLoop = !IsEdgeLive(L.getLoopLatch(), L.getHeader());
 
     // If we are going to delete the current loop completely, no extra analysis
     // is needed.
     if (DeleteCurrentLoop)

test/Transforms/LoopSimplifyCFG/live_block_marking.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; REQUIRES: asserts
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -indvars -loop-simplifycfg -debug-only=loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa 2>&1 < %s | FileCheck %s
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -passes='require<domtree>,loop(indvars,simplify-cfg)' -debug-only=loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa 2>&1 < %s | FileCheck %s
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -indvars -loop-simplifycfg -enable-mssa-loop-dependency=true -verify-memoryssa -debug-only=loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa 2>&1 < %s | FileCheck %s
 
-; This test demonstrates a bug in live blocks markup that is only catchable in
-; inter-pass interaction.
 define void @test(i1 %c) {
 ; CHECK-LABEL: @test(
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    switch i32 0, label [[ENTRY_SPLIT:%.*]] [
+; CHECK-NEXT:    i32 1, label [[DEAD_EXIT:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       entry-split:
 ; CHECK-NEXT:    br label [[OUTER:%.*]]
 ; CHECK:       outer:
 ; CHECK-NEXT:    br i1 [[C:%.*]], label [[TO_FOLD:%.*]], label [[LATCH:%.*]]
 ; CHECK:       to_fold:
 ; CHECK-NEXT:    br i1 [[C]], label [[LATCH]], label [[INNER_PREHEADER:%.*]]
 ; CHECK:       inner.preheader:
 ; CHECK-NEXT:    br label [[INNER:%.*]]
 ; CHECK:       inner:
 ; CHECK-NEXT:    br i1 false, label [[INNER_LATCH:%.*]], label [[UNDEAD:%.*]]
 ; CHECK:       inner_latch:
 ; CHECK-NEXT:    br i1 true, label [[INNER]], label [[LATCH_LOOPEXIT:%.*]]
 ; CHECK:       undead:
 ; CHECK-NEXT:    br label [[LATCH]]
 ; CHECK:       latch.loopexit:
 ; CHECK-NEXT:    br label [[LATCH]]
 ; CHECK:       latch:
-; CHECK-NEXT:    br i1 true, label [[OUTER]], label [[DEAD_EXIT:%.*]]
+; CHECK-NEXT:    br label [[OUTER]]
 ; CHECK:       dead_exit:
 ; CHECK-NEXT:    ret void
 ;
 
 entry:
   br label %outer
 
 outer: