[llvm] [SLPVectorizer] Test -1 stride loads. (PR #158358)
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Fri Sep 12 13:20:30 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-risc-v
Author: Mikhail Gudim (mgudim)
<details>
<summary>Changes</summary>
Add a test to generate -1 stride load and flags to force this behavior.
---
Full diff: https://github.com/llvm/llvm-project/pull/158358.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp (+14-1)
- (added) llvm/test/Transforms/SLPVectorizer/RISCV/reversed-strided-load.ll (+85)
``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 1cfcd3ffbd664..14a4e1f1efc82 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -198,6 +198,16 @@ static cl::opt<unsigned> MaxProfitableLoadStride(
"slp-max-stride", cl::init(8), cl::Hidden,
cl::desc("The maximum stride, considered to be profitable."));
+static cl::opt<bool>
+ DisableTreeReorder("slp-disable-tree-reorder", cl::init(false), cl::Hidden,
+ cl::desc("Disable tree reordering even if it is "
+ "profitable. Used for testing only."));
+
+static cl::opt<bool>
+ ForceStridedLoads("slp-force-strided-loads", cl::init(false), cl::Hidden,
+ cl::desc("Generate strided loads even if they are not "
+ "profitable. Used for testing only."));
+
static cl::opt<bool>
ViewSLPTree("view-slp-tree", cl::Hidden,
cl::desc("Display the SLP trees with Graphviz"));
@@ -7770,6 +7780,9 @@ static void combineOrders(MutableArrayRef<unsigned> Order,
}
bool BoUpSLP::isProfitableToReorder() const {
+ if (DisableTreeReorder)
+ return false;
+
constexpr unsigned TinyVF = 2;
constexpr unsigned TinyTree = 10;
constexpr unsigned PhiOpsLimit = 12;
@@ -13030,7 +13043,7 @@ void BoUpSLP::transformNodes() {
InstructionCost StridedCost = TTI->getStridedMemoryOpCost(
Instruction::Load, VecTy, BaseLI->getPointerOperand(),
/*VariableMask=*/false, CommonAlignment, CostKind, BaseLI);
- if (StridedCost < OriginalVecCost)
+ if (StridedCost < OriginalVecCost || ForceStridedLoads)
// Strided load is more profitable than consecutive load + reverse -
// transform the node to strided load.
E.State = TreeEntry::StridedVectorize;
diff --git a/llvm/test/Transforms/SLPVectorizer/RISCV/reversed-strided-load.ll b/llvm/test/Transforms/SLPVectorizer/RISCV/reversed-strided-load.ll
new file mode 100644
index 0000000000000..77d3ac1fb2322
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/RISCV/reversed-strided-load.ll
@@ -0,0 +1,85 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -mtriple=riscv64 -mattr=+m,+v \
+; RUN: -passes=slp-vectorizer \
+; RUN: -slp-disable-tree-reorder=true -slp-force-strided-loads=true \
+; RUN: -S < %s | FileCheck %s
+
+define void @const_stride_reversed(ptr %pl, ptr %ps) {
+; CHECK-LABEL: define void @const_stride_reversed(
+; CHECK-SAME: ptr [[PL:%.*]], ptr [[PS:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT: [[GEP_L15:%.*]] = getelementptr inbounds i8, ptr [[PL]], i64 15
+; CHECK-NEXT: [[GEP_S0:%.*]] = getelementptr inbounds i8, ptr [[PS]], i64 0
+; CHECK-NEXT: [[TMP2:%.*]] = call <16 x i8> @llvm.experimental.vp.strided.load.v16i8.p0.i64(ptr align 16 [[GEP_L15]], i64 -1, <16 x i1> splat (i1 true), i32 16)
+; CHECK-NEXT: store <16 x i8> [[TMP2]], ptr [[GEP_S0]], align 16
+; CHECK-NEXT: ret void
+;
+ %gep_l0 = getelementptr inbounds i8, ptr %pl, i64 0
+ %gep_l1 = getelementptr inbounds i8, ptr %pl, i64 1
+ %gep_l2 = getelementptr inbounds i8, ptr %pl, i64 2
+ %gep_l3 = getelementptr inbounds i8, ptr %pl, i64 3
+ %gep_l4 = getelementptr inbounds i8, ptr %pl, i64 4
+ %gep_l5 = getelementptr inbounds i8, ptr %pl, i64 5
+ %gep_l6 = getelementptr inbounds i8, ptr %pl, i64 6
+ %gep_l7 = getelementptr inbounds i8, ptr %pl, i64 7
+ %gep_l8 = getelementptr inbounds i8, ptr %pl, i64 8
+ %gep_l9 = getelementptr inbounds i8, ptr %pl, i64 9
+ %gep_l10 = getelementptr inbounds i8, ptr %pl, i64 10
+ %gep_l11 = getelementptr inbounds i8, ptr %pl, i64 11
+ %gep_l12 = getelementptr inbounds i8, ptr %pl, i64 12
+ %gep_l13 = getelementptr inbounds i8, ptr %pl, i64 13
+ %gep_l14 = getelementptr inbounds i8, ptr %pl, i64 14
+ %gep_l15 = getelementptr inbounds i8, ptr %pl, i64 15
+
+ %load0 = load i8, ptr %gep_l0 , align 16
+ %load1 = load i8, ptr %gep_l1 , align 16
+ %load2 = load i8, ptr %gep_l2 , align 16
+ %load3 = load i8, ptr %gep_l3 , align 16
+ %load4 = load i8, ptr %gep_l4 , align 16
+ %load5 = load i8, ptr %gep_l5 , align 16
+ %load6 = load i8, ptr %gep_l6 , align 16
+ %load7 = load i8, ptr %gep_l7 , align 16
+ %load8 = load i8, ptr %gep_l8 , align 16
+ %load9 = load i8, ptr %gep_l9 , align 16
+ %load10 = load i8, ptr %gep_l10, align 16
+ %load11 = load i8, ptr %gep_l11, align 16
+ %load12 = load i8, ptr %gep_l12, align 16
+ %load13 = load i8, ptr %gep_l13, align 16
+ %load14 = load i8, ptr %gep_l14, align 16
+ %load15 = load i8, ptr %gep_l15, align 16
+
+ %gep_s0 = getelementptr inbounds i8, ptr %ps, i64 0
+ %gep_s1 = getelementptr inbounds i8, ptr %ps, i64 1
+ %gep_s2 = getelementptr inbounds i8, ptr %ps, i64 2
+ %gep_s3 = getelementptr inbounds i8, ptr %ps, i64 3
+ %gep_s4 = getelementptr inbounds i8, ptr %ps, i64 4
+ %gep_s5 = getelementptr inbounds i8, ptr %ps, i64 5
+ %gep_s6 = getelementptr inbounds i8, ptr %ps, i64 6
+ %gep_s7 = getelementptr inbounds i8, ptr %ps, i64 7
+ %gep_s8 = getelementptr inbounds i8, ptr %ps, i64 8
+ %gep_s9 = getelementptr inbounds i8, ptr %ps, i64 9
+ %gep_s10 = getelementptr inbounds i8, ptr %ps, i64 10
+ %gep_s11 = getelementptr inbounds i8, ptr %ps, i64 11
+ %gep_s12 = getelementptr inbounds i8, ptr %ps, i64 12
+ %gep_s13 = getelementptr inbounds i8, ptr %ps, i64 13
+ %gep_s14 = getelementptr inbounds i8, ptr %ps, i64 14
+ %gep_s15 = getelementptr inbounds i8, ptr %ps, i64 15
+
+ store i8 %load0, ptr %gep_s15, align 16
+ store i8 %load1, ptr %gep_s14, align 16
+ store i8 %load2, ptr %gep_s13, align 16
+ store i8 %load3, ptr %gep_s12, align 16
+ store i8 %load4, ptr %gep_s11, align 16
+ store i8 %load5, ptr %gep_s10, align 16
+ store i8 %load6, ptr %gep_s9, align 16
+ store i8 %load7, ptr %gep_s8, align 16
+ store i8 %load8, ptr %gep_s7, align 16
+ store i8 %load9, ptr %gep_s6, align 16
+ store i8 %load10, ptr %gep_s5, align 16
+ store i8 %load11, ptr %gep_s4, align 16
+ store i8 %load12, ptr %gep_s3, align 16
+ store i8 %load13, ptr %gep_s2, align 16
+ store i8 %load14, ptr %gep_s1, align 16
+ store i8 %load15, ptr %gep_s0, align 16
+
+ ret void
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/158358
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