[RISCV] Commute Src in foldVMV_V_V

llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp

@@ -651,11 +651,23 @@ bool RISCVVectorPeephole::foldVMV_V_V(MachineInstr &MI) {
   if (!hasSameEEW(MI, *Src))
     return false;
 
+  std::optional<std::pair<unsigned, unsigned>> NeedsCommute;
+
   // Src needs to have the same passthru as VMV_V_V
   MachineOperand &SrcPassthru = Src->getOperand(Src->getNumExplicitDefs());
   if (SrcPassthru.getReg().isValid() &&
-      SrcPassthru.getReg() != Passthru.getReg())
-    return false;
+      SrcPassthru.getReg() != Passthru.getReg()) {
+    // If Src's passthru != Passthru, check if it uses Passthru in another
+    // operand and try to commute it.
+    int OtherIdx = Src->findRegisterUseOperandIdx(Passthru.getReg(), TRI);
+    if (OtherIdx == -1)
+      return false;
+    unsigned OpIdx1 = OtherIdx;
+    unsigned OpIdx2 = Src->getNumExplicitDefs();
+    if (!TII->findCommutedOpIndices(*Src, OpIdx1, OpIdx2))
+      return false;
+    NeedsCommute = {OpIdx1, OpIdx2};
+  }
 
   // Src VL will have already been reduced if legal (see tryToReduceVL),
   // so we don't need to handle a smaller source VL here.  However, the
@@ -668,6 +680,13 @@ bool RISCVVectorPeephole::foldVMV_V_V(MachineInstr &MI) {
   if (!ensureDominates(Passthru, *Src))
     return false;
 
+  if (NeedsCommute) {
+    auto [OpIdx1, OpIdx2] = *NeedsCommute;
+    [[maybe_unused]] bool Commuted =
+        TII->commuteInstruction(*Src, /*NewMI=*/false, OpIdx1, OpIdx2);
+    assert(Commuted && "Failed to commute Src?");
+  }
+
   if (SrcPassthru.getReg() != Passthru.getReg()) {
     SrcPassthru.setReg(Passthru.getReg());
     // If Src is masked then its passthru needs to be in VRNoV0.

llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll

@@ -245,3 +245,14 @@ define <vscale x 1 x i64> @vmerge(<vscale x 1 x i64> %passthru, <vscale x 1 x i6
   %b = call <vscale x 1 x i64> @llvm.riscv.vmv.v.v.nxv1i64(<vscale x 1 x i64> %passthru, <vscale x 1 x i64> %a, iXLen %avl)
   ret <vscale x 1 x i64> %b
 }
+
+define <vscale x 4 x float> @commute_vfmadd(<vscale x 4 x float> %passthru, <vscale x 4 x float> %a, <vscale x 4 x float> %b, iXLen %vl) {
+; CHECK-LABEL: commute_vfmadd:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e32, m2, tu, ma
+; CHECK-NEXT:    vfmacc.vv v8, v12, v10
+; CHECK-NEXT:    ret
+  %v = call <vscale x 4 x float> @llvm.riscv.vfmadd(<vscale x 4 x float> %a, <vscale x 4 x float> %b, <vscale x 4 x float> %passthru, iXLen 7, iXLen %vl, iXLen 3)
+  %w = call <vscale x 4 x float> @llvm.riscv.vmv.v.v(<vscale x 4 x float> %passthru, <vscale x 4 x float> %v, iXLen %vl)
+  ret <vscale x 4 x float> %w
+}

llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir

@@ -168,3 +168,23 @@ body: |
     %x:vrnov0 = PseudoVMERGE_VVM_M1 $noreg, %passthru, $noreg, %mask, 4, 5 /* e32 */
     %z:vr = PseudoVMV_V_V_M1 %passthru, %x, 4, 5 /* e32 */, 0 /* tu, mu */
 ...
+---
+name: commute_vfmadd
+body: |
+  bb.0:
+    liveins: $x8, $v0, $v8, $v9, $v10
+    ; CHECK-LABEL: name: commute_vfmadd
+    ; CHECK: liveins: $x8, $v0, $v8, $v9, $v10
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %avl:gprnox0 = COPY $x8
+    ; CHECK-NEXT: %passthru:vrnov0 = COPY $v8
+    ; CHECK-NEXT: %x:vr = COPY $v9
+    ; CHECK-NEXT: %y:vr = COPY $v10
+    ; CHECK-NEXT: %vfmadd:vrnov0 = nofpexcept PseudoVFMACC_VV_M1_E32 %passthru, %y, %x, 7, %avl, 5 /* e32 */, 0 /* tu, mu */, implicit $frm
+    %avl:gprnox0 = COPY $x8
+    %passthru:vrnov0 = COPY $v8
+    %x:vr = COPY $v9
+    %y:vr = COPY $v10
+    %vfmadd:vrnov0 = nofpexcept PseudoVFMADD_VV_M1_E32 %x, %y, %passthru, 7, -1, 5 /* e32 */, 3 /* ta, ma */, implicit $frm
+    %vmerge:vrnov0 = PseudoVMV_V_V_M1 %passthru, %vfmadd, %avl, 5 /* e32 */, 0 /* tu, mu */
+...