Path: utzoo!telly!philmtl!uunet!shelby!apple!usc!zaphod.mps.ohio-state.edu!tut.cis.ohio-state.edu!EDDIE.MIT.EDU!mcgill-vision!hcr!david
From: mcgill-vision!hcr!david@EDDIE.MIT.EDU
Newsgroups: gnu.gcc.bug
Subject: Bug in handling of conversion from float to double (on stack)
Message-ID: <8912141938.AA08227@zeus.UUCP>
Date: 14 Dec 89 19:38:16 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
Organization: HCR Corporation, 130 Bloor St. W., Toronto, Ontario
Lines: 64

gcc version: 1.36
os version: Interactive 386/ix 1.0.6 (System V Rel 3.1)

the following code cause a core dump when compiled with "gcc -O"

main()
{
	float f;

	f = 0;
	printf("%g, %g\n", f, f);
}

This is because the un-named instruction describing how to move a
double from a float register to the top of the stack does not take into
account the fact that popping from the 387 register stack invalidates
the contents of the register.  I would guess that the same thing would
happen on a Sun 386 system.  Here is a patch to fix the problem.  It is
similar to the code in the other (named) insn's to check if the
register is still needed.


*** md	Mon Dec 11 09:26:24 1989
--- config/i386.md	Thu Dec 14 14:29:32 1989
***************
*** 390,396 ****
        xops[2] = stack_pointer_rtx;
  /*      fp_pop_level--; */
        output_asm_insn (AS2 (sub%L0,%1,%2), xops);
!       output_asm_insn (\"fstp%S0 %0\", xops);
        RET;
      }
    return \"push%L0 %1\";
--- 390,399 ----
        xops[2] = stack_pointer_rtx;
  /*      fp_pop_level--; */
        output_asm_insn (AS2 (sub%L0,%1,%2), xops);
!       if (top_dead_p(insn))
!         output_asm_insn (\"fstp%S0 %0\", xops);
!       else
!         output_asm_insn (\"fst%S0\", xops);
        RET;
      }
    return \"push%L0 %1\";
***************
*** 426,432 ****
        xops[2] = stack_pointer_rtx;
  /*      fp_pop_level--; */
        output_asm_insn (AS2 (sub%L0,%1,%2), xops);
!       output_asm_insn (\"fstp%Q0 %0\", xops);
        RETCOM (pushdf);
      }
    else
--- 429,438 ----
        xops[2] = stack_pointer_rtx;
  /*      fp_pop_level--; */
        output_asm_insn (AS2 (sub%L0,%1,%2), xops);
!       if (top_dead_p(insn))
!         output_asm_insn (\"fstp%Q0 %0\", xops);
!       else
!         output_asm_insn (\"fst%Q0 %0\", xops);
        RETCOM (pushdf);
      }
    else