[LoopSimplifyCFG] Add check for missing loop preheader #149743
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@llvm/pr-subscribers-llvm-transforms Author: Justus Klausecker (Justus2308) ChangesCloses #147869 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). Full diff: https://github.com/llvm/llvm-project/pull/149743.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp b/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
index 221094f170ac7..c63578c63e8be 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 +218,17 @@ 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 +559,12 @@ 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..bf1b6a70e6c35
--- /dev/null
+++ b/llvm/test/Transforms/LoopSimplifyCFG/enter-through-indirectbr.ll
@@ -0,0 +1,16 @@
+; 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() {
+; CHECK-LABEL: @test(
+
+ indirectbr ptr null, [label %A, label %C]
+
+A:
+ br i1 true, label %B, label %C
+
+B:
+ br i1 true, label %A, label %C
+
+C:
+ unreachable
+}
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Requesting review from @nikic |
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Related: ziglang/zig#24383 |
llvm/test/Transforms/LoopSimplifyCFG/enter-through-indirectbr.ll
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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).
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I rebased on top of a more recent commit with passing ci, hopefully this will fix the test failures. I don't really know what I'm looking at in the logs, some lldb tests are triggering an assertion in |
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@Justus2308 Congratulations on having your first Pull Request (PR) merged into the LLVM Project! Your changes will be combined with recent changes from other authors, then tested by our build bots. If there is a problem with a build, you may receive a report in an email or a comment on this PR. Please check whether problems have been caused by your change specifically, as the builds can include changes from many authors. It is not uncommon for your change to be included in a build that fails due to someone else's changes, or infrastructure issues. How to do this, and the rest of the post-merge process, is covered in detail here. If your change does cause a problem, it may be reverted, or you can revert it yourself. This is a normal part of LLVM development. You can fix your changes and open a new PR to merge them again. If you don't get any reports, no action is required from you. Your changes are working as expected, well done! |
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/cherry-pick 0410720 |
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/pull-request #150026 |
Closes llvm#147869 Closes llvm#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 0410720)
Closes llvm#147869 Closes llvm#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).
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).