Author: Justus Klausecker Date: 2025-07-24T11:58:40+02:00 New Revision: f66e8745047ea04958e13bf02bae75ab15805e3c
URL: https://github.com/llvm/llvm-project/commit/f66e8745047ea04958e13bf02bae75ab15805e3c DIFF: https://github.com/llvm/llvm-project/commit/f66e8745047ea04958e13bf02bae75ab15805e3c.diff LOG: [LoopSimplifyCFG] Add check for missing loop preheader (#149743) Closes #147869 Closes #149679 Adds a check for a missing loop preheader during analysis. This fixes a nullptr dereference that happened whenever LoopSimplify was unable to generate a preheader because the loop was entered by an indirectbr instruction (as stated in the LoopSimplify.cpp doc comment). (cherry picked from commit 04107209856bb39e041aa38cf40de0afa90a6b2d) Added: llvm/test/Transforms/LoopSimplifyCFG/enter-through-indirectbr.ll Modified: llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp Removed: ################################################################################ diff --git a/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp b/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp index 221094f170ac7..b9546c5fa236b 100644 --- a/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp +++ b/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp @@ -128,6 +128,8 @@ class ConstantTerminatorFoldingImpl { // from any other block. So this variable set to true means that loop's latch // has become unreachable from loop header. bool DeleteCurrentLoop = false; + // Whether or not we enter the loop through an indirectbr. + bool HasIndirectEntry = false; // The blocks of the original loop that will still be reachable from entry // after the constant folding. @@ -216,6 +218,19 @@ class ConstantTerminatorFoldingImpl { return; } + // We need a loop preheader to split in handleDeadExits(). If LoopSimplify + // wasn't able to form one because the loop can be entered through an + // indirectbr we cannot continue. + if (!L.getLoopPreheader()) { + assert(any_of(predecessors(L.getHeader()), + [&](BasicBlock *Pred) { + return isa<IndirectBrInst>(Pred->getTerminator()); + }) && + "Loop should have preheader if it is not entered indirectly"); + HasIndirectEntry = true; + return; + } + // Collect live and dead loop blocks and exits. LiveLoopBlocks.insert(L.getHeader()); for (auto I = DFS.beginRPO(), E = DFS.endRPO(); I != E; ++I) { @@ -546,6 +561,12 @@ class ConstantTerminatorFoldingImpl { return false; } + if (HasIndirectEntry) { + LLVM_DEBUG(dbgs() << "Loops which can be entered indirectly are not" + " supported!\n"); + return false; + } + // Nothing to constant-fold. if (FoldCandidates.empty()) { LLVM_DEBUG( diff --git a/llvm/test/Transforms/LoopSimplifyCFG/enter-through-indirectbr.ll b/llvm/test/Transforms/LoopSimplifyCFG/enter-through-indirectbr.ll new file mode 100644 index 0000000000000..dd524ab7d140d --- /dev/null +++ b/llvm/test/Transforms/LoopSimplifyCFG/enter-through-indirectbr.ll @@ -0,0 +1,28 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5 +; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -passes='require<domtree>,loop(loop-simplifycfg)' -verify-loop-info -verify-dom-info -verify-loop-lcssa < %s | FileCheck %s + +define void @test(ptr %addr) { +; CHECK-LABEL: define void @test( +; CHECK-SAME: ptr [[ADDR:%.*]]) { +; CHECK-NEXT: indirectbr ptr [[ADDR]], [label %[[A:.*]], label %C] +; CHECK: [[A]]: +; CHECK-NEXT: br i1 true, label %[[B:.*]], label %[[C_LOOPEXIT:.*]] +; CHECK: [[B]]: +; CHECK-NEXT: br i1 true, label %[[A]], label %[[C_LOOPEXIT]] +; CHECK: [[C_LOOPEXIT]]: +; CHECK-NEXT: br label %[[C:.*]] +; CHECK: [[C]]: +; CHECK-NEXT: unreachable +; + + indirectbr ptr %addr, [label %A, label %C] + +A: + br i1 true, label %B, label %C + +B: + br i1 true, label %A, label %C + +C: + unreachable +} _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
