Re: using scratchpads to enhance RTL-level if-conversion: revised patch

[Sebastian Pop <sebpop@gmail.com>]

Abe,

please avoid comments that are not needed.

+ /* We must copy the insns between the start of the THEN block
+   and the set of 'a', if they exist, since they may be needed
+   for the converted code as well, but we must not copy a
+   start-of-BB note if one is present, nor debug "insn"s.  */
+
+ for (rtx_insn* insn = BB_HEAD (then_bb); insn && insn != insn_a
+  && insn != BB_END (then_bb); insn=NEXT_INSN (insn))
+  {

Please remove the braces: the loop body is a single stmt.

+     if (! (NOTE_INSN_BASIC_BLOCK_P (insn) || DEBUG_INSN_P (insn)))
+       duplicate_insn_chain (insn, insn);
+       /* A return of 0 from "duplicate_insn_chain" is _not_
+  a failure; it just returns the "NEXT_INSN" of the
+  last insn it duplicated.  */

Please remove this comment.

+  }
+
+ /* Done copying the needed insns between the start of the
+   THEN block and the set of 'a', if any.  */

This comment duplicates the same content as the comment before the loop.
Please remove.


On Thu, Oct 8, 2015 at 8:08 AM, Sebastian Pop <sebpop@gmail.com> wrote:
> Hi Abe,
>
> could you please avoid double negations, and
> please use early returns rather than huge right indentations:
>
> +  if (! not_a_scratchpad_candidate)
> +  {
> +    if (MEM_SIZE_KNOWN_P (orig_x))
> +    {
> +      const size_t size_of_MEM = MEM_SIZE (orig_x);
> +
> +      if (size_of_MEM <= SCRATCHPAD_MAX_SIZE)
> +      {
> [...]
> +      }
> +    }
> +  }
> +  return FALSE;
>
> Just rewrite as:
>
> if (not_a_scratchpad_candidate
>     || !MEM_SIZE_KNOWN_P (orig_x))
>   return FALSE;
>
> const size_t size_of_MEM = MEM_SIZE (orig_x);
> if (size_of_MEM > SCRATCHPAD_MAX_SIZE)
>   return FALSE;
>
> That will save 3 levels of indent.
>
> Also some of your braces do not seem to be correctly placed.
> Please use clang-format on your patch to solve the indentation issues.
>
> Thanks,
> Sebastian
>
>
> On Wed, Oct 7, 2015 at 6:29 PM, Abe <abe_skolnik@yahoo.com> wrote:
>> Dear all,
>>
>> Attached please find my revised patch to the RTL if converter.  This patch
>> enables the
>> if-conversion of half-hammocks with a store in them that the internal GCC
>> machinery
>> otherwise considers too hazardous to if-convert.  This is made safe by using
>> the
>> "scratchpad" technique, i.e. throwing away the store into a safe location
>> where nothing
>> of any importance is currently stored.  The scratchpads are allocated in the
>> stack frame.
>>
>> Here is an example of code which is newly converted with this patch,
>> at least when targeting AArch64:
>>
>>   int A[10];
>>
>>   void half_hammock() {
>>     if (A[0])
>>       A[1] = 2;
>>   }
>>
>>
>> Both tested against trunk and bootstrapped OK with defaults* on
>> AMD64-AKA-"x86_64" GNU/Linux.
>>
>> '*': [except for "--prefix"]
>>
>>
>> I`m sending the patch as an attachment to avoid it
>> being corrupted/reformatted by any e-mail troubles.
>>
>> I look forward to your feedback.
>>
>> Regards,
>>
>> Abe
>>