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

[Abe <abe_skolnik at yahoo dot com>]

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

Attachment: Abe_RTL_ifcvt_patch_1___2015_Oct._7_.patch
Description: Text document