From 0b1d069d64a394e81baf7ed022f44323095389c9 Mon Sep 17 00:00:00 2001 From: Max Kazantsev Date: Thu, 6 Dec 2018 05:45:02 +0000 Subject: [PATCH] [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 llvm-svn: 348457 --- llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp | 42 +++++-- .../LoopSimplifyCFG/constant-fold-branch.ll | 130 +++++---------------- 2 files changed, 58 insertions(+), 114 deletions(-) diff --git a/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp b/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp index 3de701e..9d5b33e 100644 --- a/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp +++ b/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp @@ -46,6 +46,8 @@ static cl::opt 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, @@ -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(); diff --git a/llvm/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll b/llvm/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll index 7998aa3..a06ada7 100644 --- a/llvm/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll +++ b/llvm/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll @@ -88,18 +88,12 @@ 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:%.*]], [[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(i32 %end) { ; 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_branch_loop(i32 %end) { ; 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_switch_loop(i32 %end) { ; 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_loop(i32 %end) { ; 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_loop(i32 %end) { ; 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_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:%.*]], [[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_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:%.*]], [[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:%.*]] -- 2.7.4