[llvm-branch-commits] [llvm] release/20.x: [CG][RISCV]Fix shuffling of odd number of input vectors (PR #125910)

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport 23b6a05ec9c2220844748487612761d1e09166b7

Requested by: @<!-- -->alexey-bataev

---
Full diff: https://github.com/llvm/llvm-project/pull/125910.diff


2 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+14-10) 
- (modified) llvm/test/CodeGen/RISCV/rvv/fixed-vectors-shuffle-exact-vlen.ll (+28) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 8d09e534b1858b..7f0646fb10dfcc 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -5214,17 +5214,21 @@ static SDValue lowerShuffleViaVRegSplitting(ShuffleVectorSDNode *SVN,
     SmallDenseMap<unsigned, SDValue, 4> Values;
     for (unsigned I : seq<unsigned>(Data.size())) {
       const auto &[Idx1, Idx2, _] = Data[I];
-      if (Values.contains(Idx1)) {
-        assert(Idx2 != UINT_MAX && Values.contains(Idx2) &&
-               "Expected both indices to be extracted already.");
-        break;
+      // If the shuffle contains permutation of odd number of elements,
+      // Idx1 might be used already in the first iteration.
+      //
+      // Idx1 = shuffle Idx1, Idx2
+      // Idx1 = shuffle Idx1, Idx3
+      SDValue &V = Values.try_emplace(Idx1).first->getSecond();
+      if (!V)
+        V = ExtractValue(Idx1 >= NumOfSrcRegs ? V2 : V1,
+                         (Idx1 % NumOfSrcRegs) * NumOpElts);
+      if (Idx2 != UINT_MAX) {
+        SDValue &V = Values.try_emplace(Idx2).first->getSecond();
+        if (!V)
+          V = ExtractValue(Idx2 >= NumOfSrcRegs ? V2 : V1,
+                           (Idx2 % NumOfSrcRegs) * NumOpElts);
       }
-      SDValue V = ExtractValue(Idx1 >= NumOfSrcRegs ? V2 : V1,
-                               (Idx1 % NumOfSrcRegs) * NumOpElts);
-      Values[Idx1] = V;
-      if (Idx2 != UINT_MAX)
-        Values[Idx2] = ExtractValue(Idx2 >= NumOfSrcRegs ? V2 : V1,
-                                    (Idx2 % NumOfSrcRegs) * NumOpElts);
     }
     SDValue V;
     for (const auto &[Idx1, Idx2, Mask] : Data) {
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-shuffle-exact-vlen.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-shuffle-exact-vlen.ll
index afd560fd74d16a..c0c17d4e0623e7 100644
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-shuffle-exact-vlen.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-shuffle-exact-vlen.ll
@@ -431,3 +431,31 @@ define void @shuffle_i256_ldst(ptr %p) vscale_range(2,2) {
   store <4 x i256> %res, ptr %p
   ret void
 }
+
+define void @shuffle_3_input_vectors() vscale_range(4,4) {
+; CHECK-LABEL: shuffle_3_input_vectors:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli a0, zero, e64, m8, ta, ma
+; CHECK-NEXT:    vmv.v.i v8, 1
+; CHECK-NEXT:    vsetivli zero, 1, e8, mf8, ta, ma
+; CHECK-NEXT:    vmv.v.i v0, 6
+; CHECK-NEXT:    vsetvli a0, zero, e64, m8, ta, ma
+; CHECK-NEXT:    vmv.v.i v16, 0
+; CHECK-NEXT:    vsetivli zero, 4, e64, m1, ta, mu
+; CHECK-NEXT:    vslidedown.vi v20, v8, 1, v0.t
+; CHECK-NEXT:    vslideup.vi v20, v9, 3
+; CHECK-NEXT:    vslidedown.vi v21, v9, 1
+; CHECK-NEXT:    vmv1r.v v22, v8
+; CHECK-NEXT:    vsetvli a0, zero, e64, m8, ta, ma
+; CHECK-NEXT:    vmsgt.vi v8, v16, 0
+; CHECK-NEXT:    vsetvli zero, zero, e32, m4, ta, ma
+; CHECK-NEXT:    vmv.x.s a0, v8
+; CHECK-NEXT:    sb a0, 0(zero)
+; CHECK-NEXT:    ret
+  %1 = shufflevector <32 x i64> zeroinitializer, <32 x i64> splat (i64 1), <32 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 16, i32 34, i32 35, i32 36, i32 37, i32 38, i32 39, i32 poison, i32 poison, i32 33, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+  %2 = icmp slt <32 x i64> zeroinitializer, %1
+  %3 = bitcast <32 x i1> %2 to i32
+  %4 = trunc i32 %3 to i8
+  store i8 %4, ptr null, align 1
+  ret void
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/125910