[PATCH] D57147: [LoopSimplifyCFG] Fix inconsistency in blocks in loop markup

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added a reviewer: rupprecht.

2nd part of D57095 <https://reviews.llvm.org/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.


https://reviews.llvm.org/D57147

Files:
  lib/Transforms/Scalar/LoopSimplifyCFG.cpp
  test/Transforms/LoopSimplifyCFG/live_block_marking.ll


Index: test/Transforms/LoopSimplifyCFG/live_block_marking.ll
===================================================================
--- test/Transforms/LoopSimplifyCFG/live_block_marking.ll
+++ test/Transforms/LoopSimplifyCFG/live_block_marking.ll
@@ -4,11 +4,13 @@
 ; 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:%.*]]
@@ -25,7 +27,7 @@
 ; 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
 ;
Index: lib/Transforms/Scalar/LoopSimplifyCFG.cpp
===================================================================
--- lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -239,7 +239,7 @@
       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.


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