[patch] Fix TARGET_MEM_REF and aliasing

[Eric Botcazou]

Hi,

up to recently the tree-ssa alias analysis engine balked at TARGET_MEM_REF.

Now it doesn't entirely anymore:

  /* First defer to TBAA if possible.  */
  if (tbaa_p
      && flag_strict_aliasing
      && !alias_sets_conflict_p (ao_ref_alias_set (ref1),
				 ao_ref_alias_set (ref2)))
    return false;

  /* If one reference is a TARGET_MEM_REF weird things are allowed.  Still
     TBAA disambiguation based on the access type is possible, so bail
     out only after that check.  */
  if ((ref1->ref && TREE_CODE (ref1->ref) == TARGET_MEM_REF)
      || (ref2->ref && TREE_CODE (ref2->ref) == TARGET_MEM_REF))
    return true;

and this is problematic for non-addressable memory references because TBAA at 
the tree level doesn't compute the correct alias set, unlike at the RTL level.

Testcase attached, compile on x86-64 at -O2.  In cddce2:

<bb 2>:
  D.2080[1]{lb: 1 sz: 4} = 1;
  D.2080[2]{lb: 1 sz: 4} = 1;
  D.2080[3]{lb: 1 sz: 4} = 1;
  D.2080[4]{lb: 1 sz: 4} = 1;
  a = D.2080;
  ivtmp.14_16 = (UNSIGNED_64) &a[1]{lb: 1 sz: 4};
  a.18_18 = (UNSIGNED_64) &a;
  D.2113_19 = a.18_18 + 16;

<bb 3>:
  # ivtmp.14_14 = PHI <ivtmp.14_15(7), ivtmp.14_16(2)>
  D.2111_17 = (long int) ivtmp.14_14;
  D.2095_9 = MEM[index: D.2111_17];

and in .dse2 the 4 initial stores are gone:

<bb 2>:
  ivtmp.14_16 = (UNSIGNED_64) &a[1]{lb: 1 sz: 4};
  a.18_18 = (UNSIGNED_64) &a;
  D.2113_19 = a.18_18 + 16;

<bb 3>:
  # ivtmp.14_14 = PHI <ivtmp.14_15(7), ivtmp.14_16(2)>
  D.2111_17 = (long int) ivtmp.14_14;
  D.2095_9 = MEM[index: D.2111_17];


Hence the attached patch, tested on i586-suse-linux, OK for mainline?


2009-11-01  Eric Botcazou  <ebotcazou@adacore.com>

	* tree.def (TARGET_MEM_REF): Update comment.
	* alias.c (get_alias_set): Retrieve the original memory reference for
	a TARGET_MEM_REF before proceeding.


2009-11-01  Eric Botcazou  <ebotcazou@adacore.com>

	* gnat.dg/opt5.adb: New test.


-- 
Eric Botcazou
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