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From: William Tambe <tambewilliam@gmail.com>
Date: Sat, 25 Apr 2020 15:21:28 -0400
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Subject: how to use emit_clobber () ?
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The following define_expand is used to generate a call to
__tls_get_addr() when the first operand of movsi is detected as a TLS
symbol by tls_symbol_operand().

I am trying to accomplish generating a call to __tls_get_addr()
passing two arguments in two registers where I would like to clobber
the first register argument.

However the use of emit_clobber() has no effect.

Any idea, how emit_clobber should be used below ?

(define_expand "movsi"
 [(set (match_operand:SI 0 "nonimmediate_operand" "")
       (match_operand:SI 1 "general_operand"      ""))]
 ""
 {
   rtx op0 = operands[0];
   rtx op1 = operands[1];
   if (tls_symbolic_operand (op0, VOIDmode)) {
     rtx arg0 = gen_rtx_REG (SImode, ARCH_FIRST_ARG_REGNUM);
     rtx arg1 = gen_rtx_REG (SImode, ARCH_FIRST_ARG_REGNUM+1);
     emit_insn (arg1);
     emit_clobber (gen__movsi (arg0, op0));
     rtx fn = gen_rtx_MEM (FUNCTION_MODE, gen_arch_tga());
     rtx_insn *insn = emit_call_insn (gen_call_value (arg0, fn, const0_rtx));
     RTL_CONST_CALL_P (insn) = 1;
     use_reg (&CALL_INSN_FUNCTION_USAGE (insn), arg0);
     use_reg (&CALL_INSN_FUNCTION_USAGE (insn), arg1);
     if (GET_CODE (op0) == MEM)
       arg0 = gen_rtx_MEM (SImode, arg0);
     operands[0] = arg0;
   }
   emit_insn (gen__movsi (operands[0], operands[1]));
   DONE;
 })