[llvm] [SLP]Disable reused reductions in revec mode for vector scalars (PR #197291)

Tue May 12 13:54:36 PDT 2026

llvmorg-github-actions[bot] wrote:




@llvm/pr-subscribers-llvm-transforms

Author: Alexey Bataev (alexey-bataev)

<details>
<summary>Changes</summary>

Reused reductions may require some special processing, but courrently it
crashes the compiler. Disable reused reductions for vector scalars in
revec mode to fix a crash.

Fixes #196914


---
Full diff: https://github.com/llvm/llvm-project/pull/197291.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp (+2-1) 
- (added) llvm/test/Transforms/SLPVectorizer/AArch64/reused-reduction-revec.ll (+68) 


``````````diff

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index f1a6eb2d7e8af..cb2901418cef2 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -28661,7 +28661,8 @@ class HorizontalReduction {
       // original scalar identity operations on matched horizontal reductions).
       IsSupportedHorRdxIdentityOp =
           RK == ReductionOrdering::Unordered && RdxKind != RecurKind::Mul &&
-          RdxKind != RecurKind::FMul && RdxKind != RecurKind::FMulAdd;
+          RdxKind != RecurKind::FMul && RdxKind != RecurKind::FMulAdd &&
+          (!SLPReVec || !S.getMainOp()->getType()->isVectorTy());
       // Gather same values.
       SmallMapVector<Value *, unsigned, 16> SameValuesCounter;
       if (IsSupportedHorRdxIdentityOp)
diff --git a/llvm/test/Transforms/SLPVectorizer/AArch64/reused-reduction-revec.ll b/llvm/test/Transforms/SLPVectorizer/AArch64/reused-reduction-revec.ll
new file mode 100644
index 0000000000000..61c8084f5d3e2
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/AArch64/reused-reduction-revec.ll
@@ -0,0 +1,68 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt --passes=slp-vectorizer -S -slp-revec -mtriple=aarch64-pc-windows-gnu < %s | FileCheck %s
+
+define <8 x i64> @test(ptr %0, <8 x i32> %1) {
+; CHECK-LABEL: define <8 x i64> @test(
+; CHECK-SAME: ptr [[TMP0:%.*]], <8 x i32> [[TMP1:%.*]]) {
+; CHECK-NEXT:  [[VECTOR_PH:.*:]]
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr i8, ptr [[TMP0]], i64 52
+; CHECK-NEXT:    [[WIDE_LOAD3:%.*]] = load <8 x i16>, ptr [[TMP2]], align 2
+; CHECK-NEXT:    [[TMP3:%.*]] = zext <8 x i16> [[WIDE_LOAD3]] to <8 x i32>
+; CHECK-NEXT:    [[TMP4:%.*]] = getelementptr i8, ptr [[TMP0]], i64 68
+; CHECK-NEXT:    [[WIDE_LOAD7:%.*]] = load <8 x i16>, ptr [[TMP4]], align 2
+; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr i8, ptr [[TMP0]], i64 36
+; CHECK-NEXT:    [[WIDE_LOAD2:%.*]] = load <8 x i16>, ptr [[TMP5]], align 2
+; CHECK-NEXT:    [[TMP6:%.*]] = zext <8 x i16> [[WIDE_LOAD2]] to <8 x i32>
+; CHECK-NEXT:    [[TMP7:%.*]] = mul <8 x i32> [[TMP1]], [[TMP6]]
+; CHECK-NEXT:    [[TMP8:%.*]] = zext <8 x i32> [[TMP7]] to <8 x i64>
+; CHECK-NEXT:    [[TMP9:%.*]] = mul <8 x i32> [[TMP1]], [[TMP3]]
+; CHECK-NEXT:    [[TMP10:%.*]] = zext <8 x i32> [[TMP9]] to <8 x i64>
+; CHECK-NEXT:    [[TMP11:%.*]] = add <8 x i64> [[TMP8]], [[TMP10]]
+; CHECK-NEXT:    [[TMP12:%.*]] = getelementptr i8, ptr [[TMP0]], i64 20
+; CHECK-NEXT:    [[WIDE_LOAD1:%.*]] = load <8 x i16>, ptr [[TMP12]], align 2
+; CHECK-NEXT:    [[TMP13:%.*]] = zext <8 x i16> [[WIDE_LOAD1]] to <8 x i32>
+; CHECK-NEXT:    [[TMP14:%.*]] = mul <8 x i32> [[TMP1]], [[TMP13]]
+; CHECK-NEXT:    [[TMP15:%.*]] = zext <8 x i32> [[TMP14]] to <8 x i64>
+; CHECK-NEXT:    [[TMP16:%.*]] = add <8 x i64> [[TMP15]], [[TMP8]]
+; CHECK-NEXT:    [[TMP17:%.*]] = add <8 x i64> [[TMP16]], [[TMP10]]
+; CHECK-NEXT:    [[TMP18:%.*]] = zext <8 x i16> [[WIDE_LOAD7]] to <8 x i32>
+; CHECK-NEXT:    [[TMP19:%.*]] = mul <8 x i32> [[TMP1]], [[TMP18]]
+; CHECK-NEXT:    [[TMP20:%.*]] = zext <8 x i32> [[TMP19]] to <8 x i64>
+; CHECK-NEXT:    [[TMP21:%.*]] = add <8 x i64> [[TMP10]], [[TMP20]]
+; CHECK-NEXT:    [[TMP22:%.*]] = add <8 x i64> [[TMP11]], [[TMP20]]
+; CHECK-NEXT:    [[BIN_RDX:%.*]] = add <8 x i64> [[TMP17]], [[TMP8]]
+; CHECK-NEXT:    [[BIN_RDX12:%.*]] = add <8 x i64> [[TMP22]], [[BIN_RDX]]
+; CHECK-NEXT:    [[BIN_RDX13:%.*]] = add <8 x i64> [[TMP21]], [[BIN_RDX12]]
+; CHECK-NEXT:    ret <8 x i64> [[BIN_RDX13]]
+;
+vector.ph:
+  %2 = getelementptr i8, ptr %0, i64 52
+  %wide.load3 = load <8 x i16>, ptr %2, align 2
+  %3 = zext <8 x i16> %wide.load3 to <8 x i32>
+  %4 = getelementptr i8, ptr %0, i64 68
+  %wide.load7 = load <8 x i16>, ptr %4, align 2
+  %5 = getelementptr i8, ptr %0, i64 36
+  %wide.load2 = load <8 x i16>, ptr %5, align 2
+  %6 = zext <8 x i16> %wide.load2 to <8 x i32>
+  %7 = mul <8 x i32> %1, %6
+  %8 = zext <8 x i32> %7 to <8 x i64>
+  %9 = mul <8 x i32> %1, %3
+  %10 = zext <8 x i32> %9 to <8 x i64>
+  %11 = add <8 x i64> %8, %10
+  %12 = getelementptr i8, ptr %0, i64 20
+  %wide.load1 = load <8 x i16>, ptr %12, align 2
+  %13 = zext <8 x i16> %wide.load1 to <8 x i32>
+  %14 = mul <8 x i32> %1, %13
+  %15 = zext <8 x i32> %14 to <8 x i64>
+  %16 = add <8 x i64> %15, %8
+  %17 = add <8 x i64> %16, %10
+  %18 = zext <8 x i16> %wide.load7 to <8 x i32>
+  %19 = mul <8 x i32> %1, %18
+  %20 = zext <8 x i32> %19 to <8 x i64>
+  %21 = add <8 x i64> %10, %20
+  %22 = add <8 x i64> %11, %20
+  %bin.rdx = add <8 x i64> %17, %8
+  %bin.rdx12 = add <8 x i64> %22, %bin.rdx
+  %bin.rdx13 = add <8 x i64> %21, %bin.rdx12
+  ret <8 x i64> %bin.rdx13
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/197291
