[CG][RISCV]Fix shuffling of odd number of input vectors

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.

Fixes llvm#125269

Reviewers: topperc, preames

Reviewed By: preames

Pull Request: llvm#125693

(cherry picked from commit 23b6a05)

Author: alexey-bataev

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -5215,17 +5215,21 @@ 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) {

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
+}