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Re: [x86] Fix gcc.c-torture/compile/20080806-1.c failures
On Mon, Nov 5, 2012 at 1:01 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Mon, Nov 5, 2012 at 9:30 AM, Richard Sandiford
> <rdsandiford@googlemail.com> wrote:
>> This is a case where we had:
>>
>> (set (reg:HI foo) (plus:HI (reg:HI sp) (const_int X)))
>> (clobber (reg:CC FLAGS_REG))
>>
>> and the splitters decided to convert it to an LEA:
>>
>> (set (reg:SI foo) (plus:SI (subreg:SI (reg:HI sp) 0) (const_int X)))
>>
>> But this fails to match, because ix86_address_subreg_operand
>> doesn't allow subregs of the stack pointer.
>>
>> This shows up an inconsistency in the way the generic code handles
>> subregs of the stack pointer. Normally we refuse to fold them, even
>> after reload, but the final_p case of alter_subreg folds them anyway.
>> That's how we ended up with the rather odd 16-bit sp.
>>
>> However, even if the special alter_subreg case was removed
>> (so that we continued to use stack_pointer_rtx itself), we'd have:
>>
>> (set (reg:HI foo) (plus:HI (subreg:HI (reg:DI sp) 0) (const_int X)))
>> (clobber (reg:CC FLAGS_REG))
>>
>> which would get converted to:
>>
>> (set (reg:SI foo) (plus:SI (subreg:SI (reg:DI sp) 0) (const_int X)))
>>
>> and we'd ICE in the same way.
>>
>> The reason x86 rejects subregs of the stack pointer is this same refusal
>> to fold. ix86_print_operand_address tries to simplify a SUBREG to a REG
>> and simplify_subreg wouldn't do anything for sp.
>>
>> simplify_subreg isn't a lot of help at the output stage though.
>> If the insn stream contains a subreg that could be simplified but
>> hasn't been, then IMO that's a bug. The cases we have to handle here
>> are those that can't be simplified (unless we decide at some point that
>> all registers must be simplifiable after reload, in which case we shouldn't
>> need to handle SUBREGs at all).
>>
>> As things stand, I think we should be using true_regnum in this case instead.
>>
>> Tested on x86_64-linux-gnu. OK to install?
>
> Let's ask H.J. to test this change on x32.
>
>> gcc/
>> PR target/55204
>> * config/i386/i386.c (ix86_address_subreg_operand): Remove stack
>> pointer check.
>> (print_reg): Use true_regnum rather than REGNO.
>> (ix86_print_operand_address): Remove SUBREG handling.
>
> The patch is OK for mainline and 4.7, if it passes H.J.'s tests with
> -maddress-mode={short,long} on x32.
>
I am on it. It will take a while.
H.J.