[Bug ipa/68273] [5/6 Regression] Wrong code on mips/mipsel with -fipa-sra

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68273

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #4 from Jeffrey A. Law <law at redhat dot com> ---
It's starting to look like a problem in tree-ssa-pre.c

Essentially we have these these key statements in various blocks:

  _10 = yyvsp_1->sym;
  _15 = yyvsp_1->sym;
  _17 = enter (_14, _15);
  _22 = MEM[(union YYSTYPE *)yyvsp_1];

Respectively _10 and _22 have the types:

(gdb) p debug_tree (cfun->gimple_df->ssa_names.m_vecdata[10]->typed.type)
 <pointer_type 0x7ffff03c6498
    type <record_type 0x7ffff0384348 Symbol type_0 SI
        size <integer_cst 0x7ffff02dd5e8 constant 32>
        unit size <integer_cst 0x7ffff02dd600 constant 4>
        align 32 symtab 0 alias set -1 canonical type 0x7ffff03842a0
        fields <field_decl 0x7ffff02ee8e8 name type <pointer_type
0x7ffff02ebe70>
            unsigned SI file j.c line 4 col 9 size <integer_cst 0x7ffff02dd5e8
32> unit size <integer_cst 0x7ffff02dd600 4>
            align 32 offset_align 64
            offset <integer_cst 0x7ffff02dd618 constant 0>
            bit offset <integer_cst 0x7ffff02dd678 constant 0> context
<record_type 0x7ffff03842a0 Symbol>> context <translation_unit_decl
0x7ffff03c80f0 D.1453>
        pointer_to_this <pointer_type 0x7ffff03c6498> chain <type_decl
0x7ffff02ee850 D.1407>>
    sizes-gimplified public unsigned SI size <integer_cst 0x7ffff02dd5e8 32>
unit size <integer_cst 0x7ffff02dd600 4>
    align 32 symtab 0 alias set -1 canonical type 0x7ffff03c6540>


(gdb) p debug_tree (cfun->gimple_df->ssa_names.m_vecdata[22]->typed.type)
 <pointer_type 0x7ffff03cd5e8
    type <record_type 0x7ffff0384498 Tnode type_0 BLK
        size <integer_cst 0x7ffff02dd678 constant 0>
        unit size <integer_cst 0x7ffff02dd618 constant 0>
        align 8 symtab 0 alias set -1 canonical type 0x7ffff03843f0 context
<translation_unit_decl 0x7ffff03c80f0 D.1453>
        pointer_to_this <pointer_type 0x7ffff0384c78> chain <type_decl
0x7ffff02eea18 D.1410>>
    sizes-gimplified unsigned SI
    size <integer_cst 0x7ffff02dd5e8 type <integer_type 0x7ffff02d6150
bitsizetype> constant 32>
    unit size <integer_cst 0x7ffff02dd600 type <integer_type 0x7ffff02d60a8
sizetype> constant 4>
    align 64 symtab 0 alias set -1 canonical type 0x7ffff0384d20>

The type of _15 is the same as the type of _10.

For reference, we're referring to instances of this structure:

union YYSTYPE
{
  Symbol *sym;
  Node rec;
};


The key thing to note from the types is they have different alignments.

Anyway, PRE detects the redundant memory reference and creates:

  # prephitmp_23 = PHI <pretmp_26(9), _10(5)>


Where _23 and _26 will have the type with the 64 bit alignment.

That node feeds this statement:

  _17 = enter (_14, prephitmp_23);

Yow!  Remember that statement previously looked like:

  _17 = enter (_14, _15);

So the alignment associated with the second argument to "enter" has changed
from 32 to 64.  That in turn may change how the argument gets passed on some
ports (mips, epiphany, maybe others).   In this specific instance is causes the
MIPS backend to align the parameter, passing it in $6 rather than where the
callee expects it ($5), which in turn results in gsoap being mis-compiled on
MIPS.

Richi -- you know the PRE code better than anyone that's currently active. 
Thoughts?