[llvm] 0e28c9b - [LAA] Skip undef/poison strides in collectStridedAccess.
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Sun Oct 26 22:01:40 PDT 2025
Author: Florian Hahn
Date: 2025-10-27T05:01:17Z
New Revision: 0e28c9bc9d64625db8e4a1707720c9eecff069a4
URL: https://github.com/llvm/llvm-project/commit/0e28c9bc9d64625db8e4a1707720c9eecff069a4
DIFF: https://github.com/llvm/llvm-project/commit/0e28c9bc9d64625db8e4a1707720c9eecff069a4.diff
LOG: [LAA] Skip undef/poison strides in collectStridedAccess.
The map returned by collectStridedAccess is used to replace strides with
their versioned values. This does not work for Undef/Poison, which don't
have use-lists. Don't try to version them, as versioning won't be useful in
practice.
Fixes https://github.com/llvm/llvm-project/issues/162922.
Added:
Modified:
llvm/lib/Analysis/LoopAccessAnalysis.cpp
llvm/test/Transforms/LoopVectorize/version-mem-access.ll
Removed:
################################################################################
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 7adb25d0e5e0d..e27a9b1c44014 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -2982,6 +2982,10 @@ void LoopAccessInfo::collectStridedAccess(Value *MemAccess) {
if (!StrideExpr)
return;
+ if (auto *Unknown = dyn_cast<SCEVUnknown>(StrideExpr))
+ if (isa<UndefValue>(Unknown->getValue()))
+ return;
+
LLVM_DEBUG(dbgs() << "LAA: Found a strided access that is a candidate for "
"versioning:");
LLVM_DEBUG(dbgs() << " Ptr: " << *Ptr << " Stride: " << *StrideExpr << "\n");
diff --git a/llvm/test/Transforms/LoopVectorize/version-mem-access.ll b/llvm/test/Transforms/LoopVectorize/version-mem-access.ll
index eb5e892a7b7b2..91b30998bf611 100644
--- a/llvm/test/Transforms/LoopVectorize/version-mem-access.ll
+++ b/llvm/test/Transforms/LoopVectorize/version-mem-access.ll
@@ -122,3 +122,96 @@ loop:
exit:
ret void
}
+
+; Make sure we do not crash when the stride is poison.
+; Test for https://github.com/llvm/llvm-project/issues/162922.
+define void @stride_poison(ptr %dst) mustprogress {
+; CHECK-LABEL: define void @stride_poison(
+; CHECK-SAME: ptr [[DST:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[UMAX:%.*]] = call i64 @llvm.umax.i64(i64 poison, i64 1)
+; CHECK-NEXT: [[TMP0:%.*]] = udiv i64 99, [[UMAX]]
+; CHECK-NEXT: [[TMP1:%.*]] = add nuw nsw i64 [[TMP0]], 2
+; CHECK-NEXT: br label %[[VECTOR_PH:.*]]
+; CHECK: [[VECTOR_PH]]:
+; CHECK-NEXT: [[N_MOD_VF:%.*]] = urem i64 [[TMP1]], 2
+; CHECK-NEXT: [[N_VEC:%.*]] = sub i64 [[TMP1]], [[N_MOD_VF]]
+; CHECK-NEXT: [[TMP2:%.*]] = mul i64 [[N_VEC]], poison
+; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
+; CHECK: [[VECTOR_BODY]]:
+; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT: [[OFFSET_IDX:%.*]] = mul i64 [[INDEX]], poison
+; CHECK-NEXT: [[TMP3:%.*]] = add i64 [[OFFSET_IDX]], poison
+; CHECK-NEXT: [[TMP4:%.*]] = add i64 [[OFFSET_IDX]], poison
+; CHECK-NEXT: [[TMP5:%.*]] = getelementptr i8, ptr [[DST]], i64 [[TMP3]]
+; CHECK-NEXT: [[TMP6:%.*]] = getelementptr i8, ptr [[DST]], i64 [[TMP4]]
+; CHECK-NEXT: store i8 0, ptr [[TMP5]], align 1
+; CHECK-NEXT: store i8 0, ptr [[TMP6]], align 1
+; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
+; CHECK-NEXT: [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT: br i1 [[TMP7]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
+; CHECK: [[MIDDLE_BLOCK]]:
+; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[TMP1]], [[N_VEC]]
+; CHECK-NEXT: br i1 [[CMP_N]], [[EXIT:label %.*]], label %[[SCALAR_PH:.*]]
+; CHECK: [[SCALAR_PH]]:
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+ %gep.dst = getelementptr i8, ptr %dst, i64 %iv
+ store i8 0, ptr %gep.dst, align 1
+ %iv.next = add nuw nsw i64 %iv, poison
+ %ec = icmp samesign ult i64 %iv, 100
+ br i1 %ec, label %loop, label %exit
+
+exit:
+ ret void
+}
+
+; Make sure we do not crash when the stride is undef.
+define void @stride_undef(ptr %dst) mustprogress {
+; CHECK-LABEL: define void @stride_undef(
+; CHECK-SAME: ptr [[DST:%.*]]) #[[ATTR0]] {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[UMAX:%.*]] = call i64 @llvm.umax.i64(i64 undef, i64 1)
+; CHECK-NEXT: [[TMP0:%.*]] = udiv i64 99, [[UMAX]]
+; CHECK-NEXT: [[TMP1:%.*]] = add nuw nsw i64 [[TMP0]], 2
+; CHECK-NEXT: br label %[[VECTOR_PH:.*]]
+; CHECK: [[VECTOR_PH]]:
+; CHECK-NEXT: [[N_MOD_VF:%.*]] = urem i64 [[TMP1]], 2
+; CHECK-NEXT: [[N_VEC:%.*]] = sub i64 [[TMP1]], [[N_MOD_VF]]
+; CHECK-NEXT: [[TMP2:%.*]] = mul i64 [[N_VEC]], undef
+; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
+; CHECK: [[VECTOR_BODY]]:
+; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT: [[OFFSET_IDX:%.*]] = mul i64 [[INDEX]], undef
+; CHECK-NEXT: [[TMP3:%.*]] = add i64 [[OFFSET_IDX]], 0
+; CHECK-NEXT: [[TMP4:%.*]] = add i64 [[OFFSET_IDX]], undef
+; CHECK-NEXT: [[TMP5:%.*]] = getelementptr i8, ptr [[DST]], i64 [[TMP3]]
+; CHECK-NEXT: [[TMP6:%.*]] = getelementptr i8, ptr [[DST]], i64 [[TMP4]]
+; CHECK-NEXT: store i8 0, ptr [[TMP5]], align 1
+; CHECK-NEXT: store i8 0, ptr [[TMP6]], align 1
+; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
+; CHECK-NEXT: [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT: br i1 [[TMP7]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
+; CHECK: [[MIDDLE_BLOCK]]:
+; CHECK-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[TMP1]], [[N_VEC]]
+; CHECK-NEXT: br i1 [[CMP_N]], [[EXIT:label %.*]], label %[[SCALAR_PH:.*]]
+; CHECK: [[SCALAR_PH]]:
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+ %gep.dst = getelementptr i8, ptr %dst, i64 %iv
+ store i8 0, ptr %gep.dst, align 1
+ %iv.next = add nuw nsw i64 %iv, undef
+ %ec = icmp samesign ult i64 %iv, 100
+ br i1 %ec, label %loop, label %exit
+
+exit:
+ ret void
+}
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