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Re: Handle data dependence relations with different bases


Richard Biener <richard.guenther@gmail.com> writes:
>>> How does this look?  Changes since v1:
>>>
>>> - Added access_fn_component_p to check for valid access function components.
>>>
>>> - Added access_fn_components_comparable_p instead of using
>>>   types_compatibloe_p directly.
>>>
>>> - Added more commentary.
>>>
>>> - Added local structures to represent the sequence, so that it's
>>>   more obvious which variables are temporaries and which aren't.
>>>
>>> - Added the test above to vect-alias-check-3.c.
>>>
>>> Tested on aarch64-linux-gnu and x86_64-linux-gnu.
>
> This is ok.

Thanks.  Just been retesting, and I think I must have forgotten
to include Ada last time.  It turns out that the patch causes a dg-scan
regression in gnat.dg/vect17.adb, because we now think that if the
array RECORD_TYPEs *do* alias in:

   procedure Add (X, Y : aliased Sarray; R : aliased out Sarray) is
   begin
      for I in Sarray'Range loop
         R(I) := X(I) + Y(I);
      end loop;
   end;

then the dependence distance must be zero.  Eric, does that hold true
for Ada?  I.e. if X and R (or Y and R) alias, must it be the case that
X(I) can only alias R(I) and not for example R(I-1) or R(I+1)?  Or are
the arrays allowed to overlap by an arbitrary number of indices?

If the assumption is correct, is the patch below OK?

Thanks,
Richard


2017-06-07  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/testsuite/
	* gnat.dg/vect17.ads (Sarray): Increase range to 1 .. 5.
	* gnat.dg/vect17.adb (Add): Create a dependence distance of 1
	when X = R or Y = R.

Index: gcc/testsuite/gnat.dg/vect17.ads
===================================================================
--- gcc/testsuite/gnat.dg/vect17.ads	2015-10-14 14:58:56.000000000 +0100
+++ gcc/testsuite/gnat.dg/vect17.ads	2017-06-07 22:10:24.796368118 +0100
@@ -1,6 +1,6 @@
 package Vect17 is
 
-   type Sarray is array (1 .. 4) of Long_Float;
+   type Sarray is array (1 .. 5) of Long_Float;
    for Sarray'Alignment use 16;
 
    procedure Add (X, Y : aliased Sarray; R : aliased out Sarray);
Index: gcc/testsuite/gnat.dg/vect17.adb
===================================================================
--- gcc/testsuite/gnat.dg/vect17.adb	2015-10-14 14:58:56.000000000 +0100
+++ gcc/testsuite/gnat.dg/vect17.adb	2017-06-07 22:10:24.796368118 +0100
@@ -5,8 +5,9 @@ package body Vect17 is
 
    procedure Add (X, Y : aliased Sarray; R : aliased out Sarray) is
    begin
-      for I in Sarray'Range loop
-         R(I) := X(I) + Y(I);
+      R(1) := X(5) + Y(5);
+      for I in 1 .. 4 loop
+         R(I + 1) := X(I) + Y(I);
       end loop;
    end;
 


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