[llvm] r348457 - [LoopSimplifyCFG] Delete dead in-loop blocks
Max Kazantsev via llvm-commits
llvm-commits at lists.llvm.org
Wed Dec 5 21:45:02 PST 2018
Author: mkazantsev
Date: Wed Dec 5 21:45:02 2018
New Revision: 348457
URL: http://llvm.org/viewvc/llvm-project?rev=348457&view=rev
Log:
[LoopSimplifyCFG] Delete dead in-loop blocks
This patch teaches LoopSimplifyCFG to delete loop blocks that have
become unreachable after terminator folding has been done.
Differential Revision: https://reviews.llvm.org/D54023
Reviewed By: anna
Modified:
llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
llvm/trunk/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
Modified: llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp?rev=348457&r1=348456&r2=348457&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp Wed Dec 5 21:45:02 2018
@@ -46,6 +46,8 @@ static cl::opt<bool> EnableTermFolding("
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,
@@ -234,6 +236,27 @@ private:
"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() {
@@ -318,15 +341,6 @@ public:
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 "
@@ -337,7 +351,8 @@ public:
// TODO: Support blocks that are not dead, but also not in loop after the
// folding.
- if (BlocksInLoopAfterFolding.size() != L.getNumBlocks()) {
+ if (BlocksInLoopAfterFolding.size() + DeadLoopBlocks.size() !=
+ L.getNumBlocks()) {
LLVM_DEBUG(
dbgs() << "Give up constant terminator folding in loop "
<< L.getHeader()->getName()
@@ -357,6 +372,13 @@ public:
// 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();
Modified: llvm/trunk/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll?rev=348457&r1=348456&r2=348457&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll (original)
+++ llvm/trunk/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll Wed Dec 5 21:45:02 2018
@@ -88,18 +88,12 @@ define i32 @dead_block_test_branch_loop(
; CHECK-NEXT: preheader:
; CHECK-NEXT: br label [[HEADER:%.*]]
; CHECK: header:
-; 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: [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[HEADER]] ]
+; 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]], [[BACKEDGE]] ]
+; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
; CHECK-NEXT: ret i32 [[I_INC_LCSSA]]
;
preheader:
@@ -129,22 +123,12 @@ define i32 @dead_block_test_switch_loop(
; CHECK-NEXT: preheader:
; CHECK-NEXT: br label [[HEADER:%.*]]
; CHECK: header:
-; 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: [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[HEADER]] ]
+; 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]], [[BACKEDGE]] ]
+; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
; CHECK-NEXT: ret i32 [[I_INC_LCSSA]]
;
preheader:
@@ -175,18 +159,12 @@ define i32 @dead_block_propogate_test_br
; CHECK-NEXT: preheader:
; CHECK-NEXT: br label [[HEADER:%.*]]
; CHECK: header:
-; 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: [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[HEADER]] ]
+; 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]], [[BACKEDGE]] ]
+; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
; CHECK-NEXT: ret i32 [[I_INC_LCSSA]]
;
preheader:
@@ -219,22 +197,12 @@ define i32 @dead_block_propogate_test_sw
; CHECK-NEXT: preheader:
; CHECK-NEXT: br label [[HEADER:%.*]]
; CHECK: header:
-; 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: [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[HEADER]] ]
+; 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]], [[BACKEDGE]] ]
+; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
; CHECK-NEXT: ret i32 [[I_INC_LCSSA]]
;
preheader:
@@ -463,32 +431,19 @@ define i32 @dead_sub_loop_test_branch_lo
; CHECK-NEXT: preheader:
; CHECK-NEXT: br label [[HEADER:%.*]]
; CHECK: header:
-; 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: [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[EXIT_A:%.*]] ]
; CHECK-NEXT: br label [[LIVE_LOOP:%.*]]
; CHECK: live_loop:
-; CHECK-NEXT: [[A:%.*]] = phi i32 [ 0, [[LIVE_PREHEADER]] ], [ [[A_INC:%.*]], [[LIVE_LOOP]] ]
+; CHECK-NEXT: [[A:%.*]] = phi i32 [ 0, [[HEADER]] ], [ [[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]], [[BACKEDGE]] ]
+; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[EXIT_A]] ]
; CHECK-NEXT: ret i32 [[I_INC_LCSSA]]
;
preheader:
@@ -536,36 +491,19 @@ define i32 @dead_sub_loop_test_switch_lo
; CHECK-NEXT: preheader:
; CHECK-NEXT: br label [[HEADER:%.*]]
; CHECK: header:
-; 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: [[I:%.*]] = phi i32 [ 0, [[PREHEADER:%.*]] ], [ [[I_INC:%.*]], [[EXIT_A:%.*]] ]
; CHECK-NEXT: br label [[LIVE_LOOP:%.*]]
; CHECK: live_loop:
-; CHECK-NEXT: [[A:%.*]] = phi i32 [ 0, [[LIVE_PREHEADER]] ], [ [[A_INC:%.*]], [[LIVE_LOOP]] ]
+; CHECK-NEXT: [[A:%.*]] = phi i32 [ 0, [[HEADER]] ], [ [[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]], [[BACKEDGE]] ]
+; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[EXIT_A]] ]
; CHECK-NEXT: ret i32 [[I_INC_LCSSA]]
;
preheader:
@@ -898,18 +836,12 @@ define i32 @partial_sub_loop_test_branch
; 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:%.*]], [[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: [[I:%.*]] = phi i32 [ 0, [[OUTER_HEADER]] ], [ [[I_INC:%.*]], [[HEADER]] ]
+; 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 [[OUTER_BACKEDGE]]
; CHECK: outer_backedge:
-; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
+; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
; 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:%.*]]
@@ -958,22 +890,12 @@ define i32 @partial_sub_loop_test_switch
; 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:%.*]], [[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: [[I:%.*]] = phi i32 [ 0, [[OUTER_HEADER]] ], [ [[I_INC:%.*]], [[HEADER]] ]
+; 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 [[OUTER_BACKEDGE]]
; CHECK: outer_backedge:
-; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[BACKEDGE]] ]
+; CHECK-NEXT: [[I_INC_LCSSA:%.*]] = phi i32 [ [[I_INC]], [[HEADER]] ]
; 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:%.*]]
More information about the llvm-commits
mailing list