Merge pull request #1904 from YenHaoChen/pr-vcompress

vcompress.vm: Check vstart value even if vl = 0

riscv/insns/vcompress_vm.h

@@ -1,14 +1,14 @@
 // vcompress vd, vs2, vs1
+require(P.any_vector_extensions());
+require(P.VU.vstart->read() == 0);
+require_align(insn.rd(), P.VU.vflmul);
+require_align(insn.rs2(), P.VU.vflmul);
 require(insn.rd() != insn.rs2());
+require_noover(insn.rd(), P.VU.vflmul, insn.rs1(), 1);
 
 reg_t pos = 0;
 
 VI_GENERAL_LOOP_BASE
-  require(P.VU.vstart->read() == 0);
-  require_align(insn.rd(), P.VU.vflmul);
-  require_align(insn.rs2(), P.VU.vflmul);
-  require_noover(insn.rd(), P.VU.vflmul, insn.rs1(), 1);
-
   const int midx = i / 64;
   const int mpos = i % 64;