[llvm] [CG][RISCV]Fix shuffling of odd number of input vectors (PR #125693)

[Alexey Bataev via llvm-commits]

https://github.com/alexey-bataev created https://github.com/llvm/llvm-project/pull/125693

If the input contains odd number of shuffled vectors, the 2 last
shuffles are shuffled with the same first vector. Need to correctly
process such situation: when the first vector is requested for the first
time - extract it from the source vector, when it is requested the
second time - reuse previous result. The second vector should be
extracted in both cases.


>From dc89ff2cf1249df057e102f861d17823eec043af Mon Sep 17 00:00:00 2001
From: Alexey Bataev <a.bataev at outlook.com>
Date: Tue, 4 Feb 2025 14:39:20 +0000
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
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Created using spr 1.3.5
---
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp   | 26 +++++++++++++----
 .../rvv/fixed-vectors-shuffle-exact-vlen.ll   | 28 +++++++++++++++++++
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 07e3390f3fbb22f..75fb909c503ec08 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -5213,13 +5213,27 @@ static SDValue lowerShuffleViaVRegSplitting(ShuffleVectorSDNode *SVN,
     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
+        if (const auto It = Values.find(Idx1);
+            I > 0 && std::get<0>(Data[I - 1]) == Idx1) {
+          assert(Idx2 != UINT_MAX && It != Values.end() &&
+                 !Values.contains(Idx2) &&
+                 "Expected only first index to be extracted already.");
+          ;
+        } else {
+          assert(Idx2 != UINT_MAX && Values.contains(Idx2) &&
+                 "Expected both indices to be extracted already.");
+          break;
+        }
+      } else {
+        SDValue V = ExtractValue(Idx1 >= NumOfSrcRegs ? V2 : V1,
+                         (Idx1 % NumOfSrcRegs) * NumOpElts);
+        Values[Idx1] = V;
       }
-      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);
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 afd560fd74d16ab..c0c17d4e0623e7b 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
+}