New regression on ARM Linux (was: Re: [PATCH] Fix regression caused by PR65310 fix)

[Alan Lawrence <alan.lawrence@arm.com>]

We've been seeing a bunch of new failures in the *libffi* testsuite on ARM Linux 
(arm-none-linux-gnueabi, arm-none-linux-gnueabihf), following this one-liner 
fix. I've reduced the testcase down to the attached (including removing any 
dependency on libffi); with gcc r221347, this prints the expected
7 8 9
whereas with gcc r221348, instead it prints
0 8 0

The action of r221348 is to change the alignment of a mem_ref, and a var_decl of 
b1, from 32 to 64; both have type
  type <record_type 0x2b9b8d428d20 cls_struct_16byte sizes-gimplified type_0 BLK
         size <integer_cst 0x2b9b8d3720a8 constant 192>
         unit size <integer_cst 0x2b9b8d372078 constant 24>
         align 64 symtab 0 alias set 1 canonical type 0x2b9b8d428d20
         fields <field_decl 0x2b9b8d42b098 a type <integer_type 0x2b9b8d092690 int>
             SI file reduced.c line 12 col 7
             size <integer_cst 0x2b9b8d08eeb8 constant 32>
             unit size <integer_cst 0x2b9b8d08eed0 constant 4>
             align 32 offset_align 64
             offset <integer_cst 0x2b9b8d08eee8 constant 0>
             bit offset <integer_cst 0x2b9b8d08ef48 constant 0> context 
<record_type 0x2b9b8d428d20 cls_struct_16byte> chain <field_decl 0x2b9b8d42b130 
b>> context <translation_unit_decl 0x2b9b8d4232d0 D.6070>
         pointer_to_this <pointer_type 0x2b9b8d42d0a8> chain <type_decl 
0x2b9b8d42b000 D.6044>>

The tree-optimized output is the same with both compilers (as this does not 
mention alignment); the expand output differs.

Still investigating...

--Alan


Richard Biener wrote:
> This fixes a vectorizer testcase regression on powerpc where SRA
> drops alignment info unnecessarily.
> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.
> 
> Richard.
> 
> 2015-03-11  Richard Biener  <rguenther@suse.de>
> 
> 	PR tree-optimization/65310
> 	* tree-sra.c (build_ref_for_offset): Also preserve larger
> 	alignment.
> 
> Index: gcc/tree-sra.c
> ===================================================================
> --- gcc/tree-sra.c	(revision 221324)
> +++ gcc/tree-sra.c	(working copy)
> @@ -1597,7 +1597,7 @@ build_ref_for_offset (location_t loc, tr
>    misalign = (misalign + offset) & (align - 1);
>    if (misalign != 0)
>      align = (misalign & -misalign);
> -  if (align < TYPE_ALIGN (exp_type))
> +  if (align != TYPE_ALIGN (exp_type))
>      exp_type = build_aligned_type (exp_type, align);
>  
>    mem_ref = fold_build2_loc (loc, MEM_REF, exp_type, base, off);
> 
>