CGEN: RELAXABLE and RELAX

CGEN: RELAXABLE and RELAX

[Dave Brolley]

Hi,

The architecture I'm working with has two load immediate insns
that look syntactically identical except for the range of the
immediate value allowed:

ld Rn,imm8	; 8 bit immediate
ld Rn,imm16	; 16 bit immediate

The 8 bit load assembles to a 16 bit insn and the 16 bit load
assembles to a 32 bit insn. From the reading the CGEN manual, it
looks to me like this is what RELAXABLE and RELAX are supposed to
handle. i.e. specifying RELAXABLE on the 8 bit load will cause it
to be tried first during assembly and specifying RELAX on the 16
bit load will cause it to be tried next. I tried this, but when I
code 'ld r1,0x100', I get an error saying bad instruction. 'ld
r1,0xff' assembles correctly. It looks like the 16 bit load was
never considered. Am I missing something?

Thanks,
Dave

CGEN: RELAXABLE and RELAX

[Doug Evans]

Dave Brolley writes:
 > The architecture I'm working with has two load immediate insns
 > that look syntactically identical except for the range of the
 > immediate value allowed:
 > 
 > ld Rn,imm8	; 8 bit immediate
 > ld Rn,imm16	; 16 bit immediate
 > 
 > The 8 bit load assembles to a 16 bit insn and the 16 bit load
 > assembles to a 32 bit insn. From the reading the CGEN manual, it
 > looks to me like this is what RELAXABLE and RELAX are supposed to
 > handle. i.e. specifying RELAXABLE on the 8 bit load will cause it
 > to be tried first during assembly and specifying RELAX on the 16
 > bit load will cause it to be tried next. I tried this, but when I
 > code 'ld r1,0x100', I get an error saying bad instruction. 'ld
 > r1,0xff' assembles correctly. It looks like the 16 bit load was
 > never considered. Am I missing something?

Hi, you're latest message reminded me I never answered this one.

IIRC, RELAXABLE,RELAX in and of themselves aren't sufficient.

Also, you're definitions of RELAXABLE,RELAX aren't quite correct.
[probably stemming from the documentation]

RELAX: don't try during assembly

From m32r_cgen_assemble_insn:

      /* If the RELAX attribute is set, this is an insn that shouldn't be
         chosen immediately.  Instead, it is used during assembler/linker
         relaxation if possible.  */
      if (CGEN_INSN_ATTR_VALUE (insn, CGEN_INSN_RELAX) != 0)
        continue;

Also, RELAX/RELAXABLE aren't generally used for this case.
What you do here is specify 8 bit loads a head of 16 bit loads.
The assembler will pick the first applicable one.

[kinda hokey, but sufficient for now]