[RISCV][MCP] Remove redundant move from tail duplication (#89865)

Tail duplication will generate the redundant move before return. It is
because the MachineCopyPropogation can't recognize COPY after post-RA
pseudoExpand.

This patch make MachineCopyPropogation recognize `%0 = ADDI %1, 0` as
COPY

Author: BeMg

llvm/lib/CodeGen/MachineCopyPropagation.cpp

@@ -1053,7 +1053,7 @@ void MachineCopyPropagation::BackwardCopyPropagateBlock(
     // Ignore non-trivial COPYs.
     std::optional<DestSourcePair> CopyOperands =
         isCopyInstr(MI, *TII, UseCopyInstr);
-    if (CopyOperands && MI.getNumOperands() == 2) {
+    if (CopyOperands) {
       Register DefReg = CopyOperands->Destination->getReg();
       Register SrcReg = CopyOperands->Source->getReg();
 

llvm/test/CodeGen/RISCV/redundant-copy-from-tail-duplicate.ll

@@ -0,0 +1,50 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc < %s -mtriple=riscv64 -mattr=+v | FileCheck %s
+
+
+define signext i32 @sum(ptr %a, i32 signext %n, i1 %prof.min.iters.check, <vscale x 8 x i1> %0, <vscale x 8 x i1> %1) {
+; CHECK-LABEL: sum:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    andi a2, a2, 1
+; CHECK-NEXT:    beqz a2, .LBB0_4
+; CHECK-NEXT:  # %bb.1: # %for.body.preheader
+; CHECK-NEXT:    li a3, 0
+; CHECK-NEXT:  .LBB0_2: # %for.body
+; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    mv a2, a3
+; CHECK-NEXT:    lw a3, 0(a0)
+; CHECK-NEXT:    addi a0, a0, 4
+; CHECK-NEXT:    bnez a1, .LBB0_2
+; CHECK-NEXT:  # %bb.3: # %for.end
+; CHECK-NEXT:    mv a0, a2
+; CHECK-NEXT:    ret
+; CHECK-NEXT:  .LBB0_4: # %vector.ph
+; CHECK-NEXT:    vsetvli a0, zero, e32, m4, ta, ma
+; CHECK-NEXT:    vmv.s.x v8, zero
+; CHECK-NEXT:    vmv.v.i v12, 0
+; CHECK-NEXT:    vsetivli zero, 1, e32, m4, ta, ma
+; CHECK-NEXT:    vredsum.vs v8, v12, v8, v0.t
+; CHECK-NEXT:    vmv.x.s a0, v8
+; CHECK-NEXT:    ret
+entry:
+  br i1 %prof.min.iters.check, label %for.body, label %vector.ph
+
+vector.ph:                                        ; preds = %entry
+  %2 = tail call i32 @llvm.vp.reduce.add.nxv8i32(i32 0, <vscale x 8 x i32> zeroinitializer, <vscale x 8 x i1> %0, i32 1)
+  br label %for.end
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
+  %red.05 = phi i32 [ %3, %for.body ], [ 0, %entry ]
+  %arrayidx = getelementptr i32, ptr %a, i64 %indvars.iv
+  %3 = load i32, ptr %arrayidx, align 4
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i32 %n, 0
+  br i1 %exitcond.not, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body, %vector.ph
+  %red.0.lcssa = phi i32 [ %2, %vector.ph ], [ %red.05, %for.body ]
+  ret i32 %red.0.lcssa
+}
+
+declare i32 @llvm.vp.reduce.add.nxv8i32(i32, <vscale x 8 x i32>, <vscale x 8 x i1>, i32)