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Re: Mips16 question...
- To: gcc at gcc dot gnu dot org, shane at minirl dot com
- Subject: Re: Mips16 question...
- From: mike stump <mrs at windriver dot com>
- Date: Wed, 29 Aug 2001 15:05:55 -0700 (PDT)
> From: Shane Nay <firstname.lastname@example.org>
> To: mike stump <email@example.com>, firstname.lastname@example.org, email@example.com
> Date: Wed, 29 Aug 2001 14:26:35 -0700
> Yea, I pulled that down, now I'm getting some strangeness from
> binutils. It's complaining about perfectly valid instructions...,
> Ugh. (2.11.2 & CVS)
:-( Dated searching with cvs isn't an uncommon way to track down
> > Shouldn't be too hard to put a ! TARGET_MIPS16 on the
> > instructions...
> Explain ..., how does this work?
That is kinda like saying, explain, how does the compiler work. The
tendancy is to say nicely, as the other explanation is about 500-1000
pages. Below I will attempt a 5 second tour. In
gcc/config/mips/mips.md, we find:
[(set (match_operand:SI 0 "register_operand" "=d")
(minus:SI (match_operand:SI 1 "reg_or_0_operand" "dJ")
(match_operand:SI 2 "arith_operand" "dI")))]
&& (GET_CODE (operands) != CONST_INT || INTVAL (operands) != -32768)"
[(set_attr "type" "arith")
(set_attr "mode" "SI")])
The above says that this instruction is not valid for MIPS16. This is
the most trivial case. In mips.c, we find:
else if (GP_REG_P (regno0))
/* Don't use X format, because that will give out of
range numbers for 64 bit host and 32 bit target. */
if (! TARGET_MIPS16)
ret = "li\t%0,%1\t\t\t# %X1";
if (INTVAL (op1) >= 0 && INTVAL (op1) <= 0xffff)
ret = "li\t%0,%1";
else if (INTVAL (op1) < 0 && INTVAL (op1) >= -0xffff)
ret = "li\t%0,%n1\n\tneg\t%0";
This means that the first insn isn't valid on the MIPS16, and the
second two are to be used instead.
> As far as MIPS16 documentation, the best I know is the VR4181
> documentation includes a pretty good instruction by instruction
> mips16<->mips32 overview.
Thanks, I added this to the readings page so I can find it next time I