Re: [GOLD] PowerPC64 toc code optimization

[Alan Modra <amodra at gmail dot com>]

On Thu, Dec 06, 2012 at 10:35:15AM -0800, Doug Kwan (éæå) wrote:
> The pattern "(insn & (0x3f << 26)) == XXX << 26" repeats so many
> times.  Why not define a predicate? It would be difficult to spot a
> typo if there was one.

Mostly because this is known good working code copied from
elf64-ppc.c.  Changing it runs the risk of the typo you're concerned
about.  :)

Also, I prefer this style in this particular case.  Someone can read
the powerpc architecture manual and be assured that the correct bits
are being compared with the correct values.  In particular, lines like
the following have all this information in one place:

	  || ((insn & (0x3f << 26)) == 58u << 26 /* lwa,ld,lmd */
	      && (insn & 3) != 1)

The alternative you propose would be something like

	  || (is_opcode(insn, 58) && (insn & 3) != 1) /* lwa,ld,lmd */

and now you need to look in two places.

-- 
Alan Modra
Australia Development Lab, IBM