Re: [PING][patch,loopiv] misaligned packed array memory access

[Zdenek Dvorak <rakdver at kam dot mff dot cuni dot cz>]

Hi,

> I'm not sure, I tried to use only `constant_multiple_of` but didn't 
> succeed without being over-conservative, because we want to check all 
> conditions of alignments of base+step+offset. Furthermore we would need 
> to duplicate most of the may_be_unaligned_p function (call to 
> get_inner_reference).

no, that is not what I ment.  What I had in mind is something like
the following patch (since we compute the step of the reference anyway,
duplicating that in loop_offset_multiple_of seems redundant):

Index: tree-ssa-loop-ivopts.c
===================================================================
*** tree-ssa-loop-ivopts.c	(revision 132341)
--- tree-ssa-loop-ivopts.c	(working copy)
*************** idx_record_use (tree base, tree *idx,
*** 1391,1400 ****
    return true;
  }
  
! /* Returns true if memory reference REF may be unaligned.  */
  
  static bool
! may_be_unaligned_p (tree ref)
  {
    tree base;
    tree base_type;
--- 1391,1400 ----
    return true;
  }
  
! /* Returns true if memory reference REF with step STEP may be unaligned.  */
  
  static bool
! may_be_unaligned_p (tree ref, tree step)
  {
    tree base;
    tree base_type;
*************** may_be_unaligned_p (tree ref)
*** 1404,1409 ****
--- 1404,1410 ----
    enum machine_mode mode;
    int unsignedp, volatilep;
    unsigned base_align;
+   double_int mul;
  
    /* TARGET_MEM_REFs are translated directly to valid MEMs on the target,
       thus they are not misaligned.  */
*************** may_be_unaligned_p (tree ref)
*** 1424,1429 ****
--- 1425,1433 ----
  	  || bitpos % BITS_PER_UNIT != 0))
      return true;
  
+   if (!constant_multiple_of (step, build_int_cst (TREE_TYPE (step), GET_MODE_ALIGNMENT (mode)), &mul))
+     return true;
+ 
    return false;
  }
  
*************** find_interesting_uses_address (struct iv
*** 1549,1555 ****
  
        /* Moreover, on strict alignment platforms, check that it is
  	 sufficiently aligned.  */
!       if (STRICT_ALIGNMENT && may_be_unaligned_p (base))
  	goto fail;
  
        base = build_fold_addr_expr (base);
--- 1553,1559 ----
  
        /* Moreover, on strict alignment platforms, check that it is
  	 sufficiently aligned.  */
!       if (STRICT_ALIGNMENT && may_be_unaligned_p (base, step))
  	goto fail;
  
        base = build_fold_addr_expr (base);