[SCEV] Make sure starting block is marked as visited when recursively collecting loop guards. #120749
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… collecting loop guards.
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@llvm/pr-subscribers-llvm-analysis Author: Julian Nagele (juliannagele) ChangesWhen Fixes #120615. Full diff: https://github.com/llvm/llvm-project/pull/120749.diff 2 Files Affected:
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 1e4bb1d606cd39..91bbe92a94c210 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -15754,6 +15754,7 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
// original header.
// TODO: share this logic with isLoopEntryGuardedByCond.
unsigned NumCollectedConditions = 0;
+ VisitedBlocks.insert(Block);
std::pair<const BasicBlock *, const BasicBlock *> Pair(Pred, Block);
for (; Pair.first;
Pair = SE.getPredecessorWithUniqueSuccessorForBB(Pair.first)) {
diff --git a/llvm/test/Analysis/ScalarEvolution/backedge-taken-count-guard-info-with-multiple-predecessors.ll b/llvm/test/Analysis/ScalarEvolution/backedge-taken-count-guard-info-with-multiple-predecessors.ll
index 81fe96a2f30c09..46dccf454f21ac 100644
--- a/llvm/test/Analysis/ScalarEvolution/backedge-taken-count-guard-info-with-multiple-predecessors.ll
+++ b/llvm/test/Analysis/ScalarEvolution/backedge-taken-count-guard-info-with-multiple-predecessors.ll
@@ -310,3 +310,29 @@ inner.header:
exit:
ret void
}
+
+; Checks correct traversal for loops without a unique predecessor
+; outside the loop.
+define void @pr120615() {
+; CHECK-LABEL: pr120615
+; CHECK-NEXT: Determining loop execution counts for: @pr120615
+; CHECK-NEXT: Loop %header: backedge-taken count is i32 0
+; CHECK-NEXT: Loop %header: constant max backedge-taken count is i32 0
+; CHECK-NEXT: Loop %header: symbolic max backedge-taken count is i32 0
+; CHECK-NEXT: Loop %header: Trip multiple is 1
+entry:
+ br label %header
+
+bb:
+ br label %header
+
+header:
+ %0 = phi i32 [ %1, %header ], [ 0, %bb ], [ 0, %entry ]
+ %1 = add i32 %0, 1
+ %icmp = icmp slt i32 %0, 0
+ br i1 %icmp, label %header, label %exit
+
+exit:
+ ret void
+
+}
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LGTM as well. Can we merge this? |
Collaborator
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/73/builds/10995 Here is the relevant piece of the build log for the reference |
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Jan 6, 2025
… collecting loop guards. (llvm#120749) When `collectFromBlock` is called without a predecessor (in particular for loops that don't have a unique predecessor outside the loop) we never start climbing the predecessor chain, and thus don't mark the starting block as visited. Fixes llvm#120615. (cherry picked from commit f035351)
juliannagele
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to swiftlang/llvm-project
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Jan 6, 2025
…9797) * [SCEV] Fix exit condition for recursive loop guard collection (llvm#120442) When assumptions are present `Terms.size()` does not actually count the number of conditions collected from dominating branches; introduce a separate counter. Fixes llvm#120237 (cherry picked from commit acfd26a) * [SCEV] Make sure starting block is marked as visited when recursively collecting loop guards. (llvm#120749) When `collectFromBlock` is called without a predecessor (in particular for loops that don't have a unique predecessor outside the loop) we never start climbing the predecessor chain, and thus don't mark the starting block as visited. Fixes llvm#120615. (cherry picked from commit f035351)
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When
collectFromBlockis called without a predecessor (in particular for loops that don't have a unique predecessor outside the loop) we never start climbing the predecessor chain, and thus don't mark the starting block as visited.Fixes #120615.