The following test point shows different register encoding for IMULL with imm operands in opto and jit assembly.

Opto:
025 imulq R17, [R16 + #120 (8-bit)], #13104 # long
JIT:
  0x00007d44a7e80f27: imul $0x3330,0x78(%rax),%ecx

imul is a MAP0/1 instruction which should emit REX2 encoding with EGPR operands.

Following four selection patterns needs to be analysed as they are missing UseAPX predication.

instruct mulI_rReg_imm(rRegI dst, rRegI src, immI imm, rFlagsReg cr)
%{
  match(Set dst (MulI src imm));
  effect(KILL cr, TEMP_DEF dst);

instruct mulI_mem_imm(rRegI dst, memory src, immI imm, rFlagsReg cr)
%{
  match(Set dst (MulI (LoadI src) imm));
  effect(KILL cr, TEMP dst);

instruct mulL_rReg_imm(rRegL dst, rRegL src, immL32 imm, rFlagsReg cr)
%{
  match(Set dst (MulL src imm));
  effect(KILL cr, TEMP_DEF dst);

instruct mulL_mem_imm(rRegL dst, memory src, immL32 imm, rFlagsReg cr)
%{
  match(Set dst (MulL (LoadL src) imm));
  effect(KILL cr, TEMP dst);