Revert "[LoopSimplifyCFG] Delete dead in-loop blocks"

This reverts commit r348457.
The original commit causes clang to crash when doing an instrumented
build with a new pass manager. Reverting to unbreak our integrate.

llvm-svn: 348484

Author: ilya-biryukov

llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp

@@ -46,8 +46,6 @@ static cl::opt<bool> EnableTermFolding("enable-loop-simplifycfg-term-folding",
 
 STATISTIC(NumTerminatorsFolded,
           "Number of terminators folded to unconditional branches");
-STATISTIC(NumLoopBlocksDeleted,
-          "Number of loop blocks deleted");
 
 /// If \p BB is a switch or a conditional branch, but only one of its successors
 /// can be reached from this block in runtime, return this successor. Otherwise,
@@ -236,27 +234,6 @@ class ConstantTerminatorFoldingImpl {
            "All blocks that stay in loop should be live!");
   }
 
-  /// Delete loop blocks that have become unreachable after folding. Make all
-  /// relevant updates to DT and LI.
-  void deleteDeadLoopBlocks() {
-    DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
-    if (MSSAU)
-      MSSAU->removeBlocks(DeadLoopBlocks);
-    for (auto *BB : DeadLoopBlocks) {
-      assert(BB != L.getHeader() &&
-             "Header of the current loop cannot be dead!");
-      LLVM_DEBUG(dbgs() << "Deleting dead loop block " << BB->getName()
-                        << "\n");
-      if (LI.isLoopHeader(BB)) {
-        assert(LI.getLoopFor(BB) != &L && "Attempt to remove current loop!");
-        LI.erase(LI.getLoopFor(BB));
-      }
-      LI.removeBlock(BB);
-      DeleteDeadBlock(BB, &DTU);
-      ++NumLoopBlocksDeleted;
-    }
-  }
-
   /// Constant-fold terminators of blocks acculumated in FoldCandidates into the
   /// unconditional branches.
   void foldTerminators() {
@@ -341,6 +318,15 @@ class ConstantTerminatorFoldingImpl {
       return false;
     }
 
+    // TODO: Support deletion of dead loop blocks.
+    if (!DeadLoopBlocks.empty()) {
+      LLVM_DEBUG(dbgs() << "Give up constant terminator folding in loop "
+                        << L.getHeader()->getName()
+                        << ": we don't currently"
+                           " support deletion of dead in-loop blocks.\n");
+      return false;
+    }
+
     // TODO: Support dead loop exits.
     if (!DeadExitBlocks.empty()) {
       LLVM_DEBUG(dbgs() << "Give up constant terminator folding in loop "
@@ -351,8 +337,7 @@ class ConstantTerminatorFoldingImpl {
 
     // TODO: Support blocks that are not dead, but also not in loop after the
     // folding.
-    if (BlocksInLoopAfterFolding.size() + DeadLoopBlocks.size() !=
-        L.getNumBlocks()) {
+    if (BlocksInLoopAfterFolding.size() != L.getNumBlocks()) {
       LLVM_DEBUG(
           dbgs() << "Give up constant terminator folding in loop "
                  << L.getHeader()->getName()
@@ -372,13 +357,6 @@ class ConstantTerminatorFoldingImpl {
     // Make the actual transforms.
     foldTerminators();
 
-    if (!DeadLoopBlocks.empty()) {
-      LLVM_DEBUG(dbgs() << "Deleting " << DeadLoopBlocks.size()
-                    << " dead blocks in loop " << L.getHeader()->getName()
-                    << "\n");
-      deleteDeadLoopBlocks();
-    }
-
 #ifndef NDEBUG
     // Make sure that we have preserved all data structures after the transform.
     DT.verify();

llvm/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll

@@ -88,12 +88,18 @@ define i32 @dead_block_test_branch_loop(i32 %end) {
 ; CHECK-NEXT:  preheader:
 ; CHECK-NEXT:    br label [[HEADER:%.*]]
 ; CHECK:       header:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[HEADER]] ]
-; CHECK-NEXT:    [[I_INC]] = add i32 [[I]], 1
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    br i1 true, label [[BACKEDGE]], label [[DEAD:%.*]]
+; CHECK:       dead:
+; CHECK-NEXT:    [[I_2:%.*]] = add i32 [[I]], 1
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[I_1:%.*]] = phi i32 [ [[I]], [[HEADER]] ], [ [[I_2]], [[DEAD]] ]
+; CHECK-NEXT:    [[I_INC]] = add i32 [[I_1]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I_INC]], [[END:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[HEADER]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
+; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
 ; CHECK-NEXT:    ret i32 [[I_INC_LCSSA]]
 ;
 preheader:
@@ -123,12 +129,22 @@ define i32 @dead_block_test_switch_loop(i32 %end) {
 ; CHECK-NEXT:  preheader:
 ; CHECK-NEXT:    br label [[HEADER:%.*]]
 ; CHECK:       header:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[HEADER]] ]
-; CHECK-NEXT:    [[I_INC]] = add i32 [[I]], 1
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    switch i32 1, label [[DEAD:%.*]] [
+; CHECK-NEXT:    i32 0, label [[DEAD]]
+; CHECK-NEXT:    i32 1, label [[BACKEDGE]]
+; CHECK-NEXT:    i32 2, label [[DEAD]]
+; CHECK-NEXT:    ]
+; CHECK:       dead:
+; CHECK-NEXT:    [[I_2:%.*]] = add i32 [[I]], 1
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[I_1:%.*]] = phi i32 [ [[I]], [[HEADER]] ], [ [[I_2]], [[DEAD]] ]
+; CHECK-NEXT:    [[I_INC]] = add i32 [[I_1]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I_INC]], [[END:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[HEADER]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
+; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
 ; CHECK-NEXT:    ret i32 [[I_INC_LCSSA]]
 ;
 preheader:
@@ -159,12 +175,18 @@ define i32 @dead_block_propogate_test_branch_loop(i32 %end) {
 ; CHECK-NEXT:  preheader:
 ; CHECK-NEXT:    br label [[HEADER:%.*]]
 ; CHECK:       header:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[HEADER]] ]
-; CHECK-NEXT:    [[I_INC]] = add i32 [[I]], 1
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    br i1 true, label [[BACKEDGE]], label [[DEAD:%.*]]
+; CHECK:       dead:
+; CHECK-NEXT:    [[I_2:%.*]] = add i32 [[I]], 1
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[I_1:%.*]] = phi i32 [ [[I]], [[HEADER]] ], [ [[I_2]], [[DEAD]] ]
+; CHECK-NEXT:    [[I_INC]] = add i32 [[I_1]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I_INC]], [[END:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[HEADER]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
+; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
 ; CHECK-NEXT:    ret i32 [[I_INC_LCSSA]]
 ;
 preheader:
@@ -197,12 +219,22 @@ define i32 @dead_block_propogate_test_switch_loop(i32 %end) {
 ; CHECK-NEXT:  preheader:
 ; CHECK-NEXT:    br label [[HEADER:%.*]]
 ; CHECK:       header:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[HEADER]] ]
-; CHECK-NEXT:    [[I_INC]] = add i32 [[I]], 1
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    switch i32 1, label [[DEAD:%.*]] [
+; CHECK-NEXT:    i32 0, label [[DEAD]]
+; CHECK-NEXT:    i32 1, label [[BACKEDGE]]
+; CHECK-NEXT:    i32 2, label [[DEAD]]
+; CHECK-NEXT:    ]
+; CHECK:       dead:
+; CHECK-NEXT:    [[I_2:%.*]] = add i32 [[I]], 1
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[I_1:%.*]] = phi i32 [ [[I]], [[HEADER]] ], [ [[I_2]], [[DEAD]] ]
+; CHECK-NEXT:    [[I_INC]] = add i32 [[I_1]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I_INC]], [[END:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[HEADER]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
+; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
 ; CHECK-NEXT:    ret i32 [[I_INC_LCSSA]]
 ;
 preheader:
@@ -431,19 +463,32 @@ define i32 @dead_sub_loop_test_branch_loop(i32 %end) {
 ; CHECK-NEXT:  preheader:
 ; CHECK-NEXT:    br label [[HEADER:%.*]]
 ; CHECK:       header:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[EXIT_A:%.*]] ]
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    br i1 true, label [[LIVE_PREHEADER:%.*]], label [[DEAD_PREHEADER:%.*]]
+; CHECK:       live_preheader:
 ; CHECK-NEXT:    br label [[LIVE_LOOP:%.*]]
 ; CHECK:       live_loop:
-; CHECK-NEXT:    [[A:%.*]] = phi i32 [ 0, [[HEADER]] ], [ [[A_INC:%.*]], [[LIVE_LOOP]] ]
+; CHECK-NEXT:    [[A:%.*]] = phi i32 [ 0, [[LIVE_PREHEADER]] ], [ [[A_INC:%.*]], [[LIVE_LOOP]] ]
 ; CHECK-NEXT:    [[A_INC]] = add i32 [[A]], 1
 ; CHECK-NEXT:    [[CMP_A:%.*]] = icmp slt i32 [[A_INC]], [[END:%.*]]
-; CHECK-NEXT:    br i1 [[CMP_A]], label [[LIVE_LOOP]], label [[EXIT_A]]
+; CHECK-NEXT:    br i1 [[CMP_A]], label [[LIVE_LOOP]], label [[EXIT_A:%.*]]
 ; CHECK:       exit.a:
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       dead_preheader:
+; CHECK-NEXT:    br label [[DEAD_LOOP:%.*]]
+; CHECK:       dead_loop:
+; CHECK-NEXT:    [[B:%.*]] = phi i32 [ 0, [[DEAD_PREHEADER]] ], [ [[B_INC:%.*]], [[DEAD_LOOP]] ]
+; CHECK-NEXT:    [[B_INC]] = add i32 [[B]], 1
+; CHECK-NEXT:    [[CMP_B:%.*]] = icmp slt i32 [[B_INC]], [[END]]
+; CHECK-NEXT:    br i1 [[CMP_B]], label [[DEAD_LOOP]], label [[EXIT_B:%.*]]
+; CHECK:       exit.b:
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       backedge:
 ; CHECK-NEXT:    [[I_INC]] = add i32 [[I]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I_INC]], [[END]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[HEADER]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[EXIT_A]] ]
+; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
 ; CHECK-NEXT:    ret i32 [[I_INC_LCSSA]]
 ;
 preheader:
@@ -491,19 +536,36 @@ define i32 @dead_sub_loop_test_switch_loop(i32 %end) {
 ; CHECK-NEXT:  preheader:
 ; CHECK-NEXT:    br label [[HEADER:%.*]]
 ; CHECK:       header:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[EXIT_A:%.*]] ]
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    switch i32 1, label [[DEAD_PREHEADER:%.*]] [
+; CHECK-NEXT:    i32 0, label [[DEAD_PREHEADER]]
+; CHECK-NEXT:    i32 1, label [[LIVE_PREHEADER:%.*]]
+; CHECK-NEXT:    i32 2, label [[DEAD_PREHEADER]]
+; CHECK-NEXT:    ]
+; CHECK:       live_preheader:
 ; CHECK-NEXT:    br label [[LIVE_LOOP:%.*]]
 ; CHECK:       live_loop:
-; CHECK-NEXT:    [[A:%.*]] = phi i32 [ 0, [[HEADER]] ], [ [[A_INC:%.*]], [[LIVE_LOOP]] ]
+; CHECK-NEXT:    [[A:%.*]] = phi i32 [ 0, [[LIVE_PREHEADER]] ], [ [[A_INC:%.*]], [[LIVE_LOOP]] ]
 ; CHECK-NEXT:    [[A_INC]] = add i32 [[A]], 1
 ; CHECK-NEXT:    [[CMP_A:%.*]] = icmp slt i32 [[A_INC]], [[END:%.*]]
-; CHECK-NEXT:    br i1 [[CMP_A]], label [[LIVE_LOOP]], label [[EXIT_A]]
+; CHECK-NEXT:    br i1 [[CMP_A]], label [[LIVE_LOOP]], label [[EXIT_A:%.*]]
 ; CHECK:       exit.a:
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       dead_preheader:
+; CHECK-NEXT:    br label [[DEAD_LOOP:%.*]]
+; CHECK:       dead_loop:
+; CHECK-NEXT:    [[B:%.*]] = phi i32 [ 0, [[DEAD_PREHEADER]] ], [ [[B_INC:%.*]], [[DEAD_LOOP]] ]
+; CHECK-NEXT:    [[B_INC]] = add i32 [[B]], 1
+; CHECK-NEXT:    [[CMP_B:%.*]] = icmp slt i32 [[B_INC]], [[END]]
+; CHECK-NEXT:    br i1 [[CMP_B]], label [[DEAD_LOOP]], label [[EXIT_B:%.*]]
+; CHECK:       exit.b:
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       backedge:
 ; CHECK-NEXT:    [[I_INC]] = add i32 [[I]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I_INC]], [[END]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[HEADER]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[EXIT_A]] ]
+; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
 ; CHECK-NEXT:    ret i32 [[I_INC_LCSSA]]
 ;
 preheader:
@@ -836,12 +898,18 @@ define i32 @partial_sub_loop_test_branch_loop(i32 %end) {
 ; CHECK-NEXT:    [[J:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[J_INC:%.*]], [[OUTER_BACKEDGE:%.*]] ]
 ; CHECK-NEXT:    br label [[HEADER:%.*]]
 ; CHECK:       header:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[OUTER_HEADER]] ], [ [[I_INC:%.*]], [[HEADER]] ]
-; CHECK-NEXT:    [[I_INC]] = add i32 [[I]], 1
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[OUTER_HEADER]] ], [ [[I_INC:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    br i1 true, label [[BACKEDGE]], label [[DEAD:%.*]]
+; CHECK:       dead:
+; CHECK-NEXT:    [[I_2:%.*]] = add i32 [[I]], 1
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[I_1:%.*]] = phi i32 [ [[I]], [[HEADER]] ], [ [[I_2]], [[DEAD]] ]
+; CHECK-NEXT:    [[I_INC]] = add i32 [[I_1]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I_INC]], [[END:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[HEADER]], label [[OUTER_BACKEDGE]]
 ; CHECK:       outer_backedge:
-; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
+; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
 ; CHECK-NEXT:    [[J_INC]] = add i32 [[J]], 1
 ; CHECK-NEXT:    [[CMP_J:%.*]] = icmp slt i32 [[J_INC]], [[END]]
 ; CHECK-NEXT:    br i1 [[CMP_J]], label [[OUTER_HEADER]], label [[EXIT:%.*]]
@@ -890,12 +958,22 @@ define i32 @partial_sub_loop_test_switch_loop(i32 %end) {
 ; CHECK-NEXT:    [[J:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[J_INC:%.*]], [[OUTER_BACKEDGE:%.*]] ]
 ; CHECK-NEXT:    br label [[HEADER:%.*]]
 ; CHECK:       header:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[OUTER_HEADER]] ], [ [[I_INC:%.*]], [[HEADER]] ]
-; CHECK-NEXT:    [[I_INC]] = add i32 [[I]], 1
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[OUTER_HEADER]] ], [ [[I_INC:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    switch i32 1, label [[DEAD:%.*]] [
+; CHECK-NEXT:    i32 0, label [[DEAD]]
+; CHECK-NEXT:    i32 1, label [[BACKEDGE]]
+; CHECK-NEXT:    i32 2, label [[DEAD]]
+; CHECK-NEXT:    ]
+; CHECK:       dead:
+; CHECK-NEXT:    [[I_2:%.*]] = add i32 [[I]], 1
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[I_1:%.*]] = phi i32 [ [[I]], [[HEADER]] ], [ [[I_2]], [[DEAD]] ]
+; CHECK-NEXT:    [[I_INC]] = add i32 [[I_1]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[I_INC]], [[END:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[HEADER]], label [[OUTER_BACKEDGE]]
 ; CHECK:       outer_backedge:
-; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
+; CHECK-NEXT:    [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
 ; CHECK-NEXT:    [[J_INC]] = add i32 [[J]], 1
 ; CHECK-NEXT:    [[CMP_J:%.*]] = icmp slt i32 [[J_INC]], [[END]]
 ; CHECK-NEXT:    br i1 [[CMP_J]], label [[OUTER_HEADER]], label [[EXIT:%.*]]