[PATCH] D56121: [LoopSimplifyCFG] Fix order of deletion of complex dead subloops

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: anna, fedor.sergeev, skatkov, reames.

Function `DeleteDeadBlock` requires that all predecessors of a block
being deleted have already been deleted, with the exception of a
single-block loop. When we use it for removal of dead subloops that
contain more than one block, we may not fulfull this requirement and
fail an assertion.

This patch replaces invocation of `DeleteDeadBlock` with a generalized
version `DeleteDeadBlocks` that is able to deal with multiple dead blocks,
even if they contain some cycles.


https://reviews.llvm.org/D56121

Files:
  lib/Transforms/Scalar/LoopSimplifyCFG.cpp
  test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll


Index: test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
===================================================================
--- test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
+++ test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
@@ -1,7 +1,4 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; XFAIL: *
-; Tests complex_dead_subloop_branch and complex_dead_subloop_switch fail an
-; assertion, therefore the CFG simplification is temporarily disabled.
 ; REQUIRES: asserts
 ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -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(simplify-cfg)' -debug-only=loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa 2>&1 < %s | FileCheck %s
@@ -2512,6 +2509,15 @@
 }
 
 define i32 @complex_dead_subloop_branch(i1 %cond1, i1 %cond2, i1 %cond3) {
+; CHECK-LABEL: @complex_dead_subloop_branch(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    br i1 [[COND3:%.*]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[RESULT_LCSSA:%.*]] = phi i32 [ 0, [[LOOP]] ]
+; CHECK-NEXT:    ret i32 [[RESULT_LCSSA]]
+;
 entry:
   br label %loop
 
@@ -2540,6 +2546,15 @@
 }
 
 define i32 @complex_dead_subloop_switch(i1 %cond1, i1 %cond2, i1 %cond3) {
+; CHECK-LABEL: @complex_dead_subloop_switch(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    br i1 [[COND3:%.*]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[RESULT_LCSSA:%.*]] = phi i32 [ 0, [[LOOP]] ]
+; CHECK-NEXT:    ret i32 [[RESULT_LCSSA]]
+;
 entry:
   br label %loop
 
Index: lib/Transforms/Scalar/LoopSimplifyCFG.cpp
===================================================================
--- lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -400,9 +400,10 @@
         LI.erase(LI.getLoopFor(BB));
       }
       LI.removeBlock(BB);
-      DeleteDeadBlock(BB, &DTU);
-      ++NumLoopBlocksDeleted;
     }
+
+    DeleteDeadBlocks(DeadLoopBlocks, &DTU);
+    NumLoopBlocksDeleted += DeadLoopBlocks.size();
   }
 
   /// Constant-fold terminators of blocks acculumated in FoldCandidates into the


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