[tree-ssa] string builtins strikes back

[Jan Hubicka]

Hi,
the folling testcase (derived from testsuite):

extern void abort (void);
extern __SIZE_TYPE__ strlen (const char *);

int x = 6;

void
main_test (void)
{
  const char *const foo = "hello world";

  if (strlen (foo + (x++ & 7)) != 5)
    abort ();
}
Causes fold_stmt to turn gimple:
 <call_expr 0x40195678
    type <integer_type 0x40196570 unsigned int unsigned SI
        size <integer_cst 0x40194288 constant invariant 32>
        unit size <integer_cst 0x40194330 constant invariant 4>
        align 32 symtab 0 alias set -1 precision 32 min <integer_cst 0x40194378 0> max <integer_cst 0x40194390 4294967295>>
    nothrow
    arg 0 <addr_expr 0x401a45e0
        type <pointer_type 0x40267570 type <function_type 0x401d16cc>
            unsigned SI
            size <integer_cst 0x40194978 constant invariant 32>
            unit size <integer_cst 0x401949d8 constant invariant 4>
            align 32 symtab 0 alias set -1>
        constant invariant
        arg 0 <function_decl 0x40264740 strlen type <function_type 0x401d16cc>
            addressable used nothrow public external built-in defer-output QI file a.c line 2
            built-in BUILT_IN_NORMAL:BUILT_IN_STRLEN context <translation_unit_decl 0x4019615c> attributes <tree_list 0x401d2048>
            (mem:QI (symbol_ref:SI ("strlen") [flags 0x41] <function_decl 0x401d1740 strlen>) [0 S1 A8]) chain <function_decl 0x40264984 strcmp>>>
    arg 1 <tree_list 0x40266930
        value <ssa_name 0x40266cf0 type <pointer_type 0x4026732c>
           >>
    a.c:15>

Into non-gimple:
 <nop_expr 0x4026a000
    type <integer_type 0x40196570 unsigned int unsigned SI
        size <integer_cst 0x40194288 constant invariant 32>
        unit size <integer_cst 0x40194330 constant invariant 4>
        align 32 symtab 0 alias set -1 precision 32 min <integer_cst 0x40194378 0> max <integer_cst 0x40194390 4294967295>>

    arg 0 <minus_expr 0x401959d8
        type <integer_type 0x4019d89c sizetype SI
            size <integer_cst 0x40194978 constant invariant 32>
            unit size <integer_cst 0x401949d8 constant invariant 4>
            align 32 symtab 0 alias set -1 precision 32 min <integer_cst 0x401949a8 -2147483648> max <integer_cst 0x401949c0 2147483647>>

        arg 0 <integer_cst 0x402668a0 constant invariant 11>
        arg 1 <nop_expr 0x401a4fa0 type <integer_type 0x4019d89c>

            arg 0 <ssa_name 0x40266cd8 type <integer_type 0x40196570 unsigned int>
               >>>>

What would be best to cope with this?  (in this case proper folding of nops
would elliminate them) but in general I don't think this is possible in all
side cases of string builtins.
Do we want the fold_stmt to produce possibly multiple statement when this
simplifies things down?  What should be the interface here?

Honza