Re: ADDR_SPACE_CONVERT_EXPR always expanded to 0?

[Richard Biener <richard dot guenther at gmail dot com>]

On Fri, Mar 8, 2013 at 2:57 PM, Georg-Johann Lay <avr@gjlay.de> wrote:
> While implementing PR56263 (Strict address-space checking for AVR), I
> encountered the problem that pointer casts with address spaces are always
> expanded as const_int 0.
>
> The problem occurs if the attached patch that implements PR56263 and the
> following code is compiled as
>
> $ avr-gcc -Os flash-cast.c -S -mstrict-addr-space-subsets
>
>
> #define PROGMEM __attribute__((__progmem__))
>
> #define PSTR(s)                                                         \
>   (__extension__                                                        \
>    ({                                                                   \
>      static const char __c[] PROGMEM = (s);                             \
>      &__c[0];                                                           \
>    }))
>
> extern void print (const __memx char*, ...);
>
> const __flash char *p;
>
> void f (const char *c)
> {
>     c = (const char*) p;
>
>     print ((const __flash char*) PSTR ("Hallo flash"));
> }
>
>
>
> The corresponding .expand dump reads:
>
>
> f (const char * c)
> {
>   static const char __c[12] = "Hallo flash";
>   const <address-space-1> char * _2;
>   const <address-space-7> char * _3;
>
> ;;   basic block 2, loop depth 0
> ;;    pred:       ENTRY
>   _2 = (const <address-space-1> char *) (&__c[0]);
>   _3 = (const <address-space-7> char *) _2;
>   print (_3); [tail call]
>   return;
> ;;    succ:       EXIT
>
> }
>
>
> but the expression is always emit as (const_int 0).
>
>
> Trying to track this issue, I ended up in build1_stat which enters the default
> case for "code" (ADDR_SPACE_CONVERT_EXPR at that time) and returns the
> following tree:
>
>
> (gdb) p t
> $62 = (tree) 0xb7bb4578
> (gdb) pt
>  <addr_space_convert_expr 0xb7bb4578
>     type <pointer_type 0xb7bc3a80
>         type <integer_type 0xb7bc3a20 char readonly sizes-gimplified
> address-space-1 string-flag QI
>             size <integer_cst 0xb7b3a1a4 constant 8>
>             unit size <integer_cst 0xb7b3a1b8 constant 1>
>             align 8 symtab 0 alias set -1 canonical type 0xb7bc3a20 precision 8
> min <integer_cst 0xb7b3a1e0 -128> max <integer_cst 0xb7b3a208 127>
>             pointer_to_this <pointer_type 0xb7bc3a80>>
>         unsigned HI
>         size <integer_cst 0xb7b3a08c constant 16>
>         unit size <integer_cst 0xb7b3a0a0 constant 2>
>         align 8 symtab 0 alias set -1 canonical type 0xb7bc3a80>
>     readonly constant
>     arg 0 <addr_expr 0xb7bb449c
>         type <pointer_type 0xb7b4f2a0 type <integer_type 0xb7b4f240 char>
>             public unsigned HI size <integer_cst 0xb7b3a08c 16> unit size
> <integer_cst 0xb7b3a0a0 2>
>             align 8 symtab 0 alias set -1 canonical type 0xb7b4f2a0
>             pointer_to_this <pointer_type 0xb7b4f840>>
>         readonly constant
>         arg 0 <array_ref 0xb7b465a0 type <integer_type 0xb7b4f240 char>
>             readonly arg 0 <var_decl 0xb7bcd05c __c>
>             arg 1 <integer_cst 0xb7b3a460 constant 0>
>             flash-cast.c:18:128>
>         flash-cast.c:18:124>>
>
> Problem is the arg 1 <integer_cst 0xb7b3a460 constant 0> at the end which leads
> to the expansion of 0.
>
> The call chain is:
>
> #0  build1_stat (code=ADDR_SPACE_CONVERT_EXPR, type=0xb7bc3a80,
> node=0xb7bb449c) at ../../../gcc.gnu.org/trunk/gcc/tree.c:3848
> (gdb) bt
> #0  build1_stat (code=ADDR_SPACE_CONVERT_EXPR, type=0xb7bc3a80,
> node=0xb7bb449c) at ../../../gcc.gnu.org/trunk/gcc/tree.c:3848
> #1  0x08286be0 in gimple_assign_rhs_to_tree (stmt=0xb7bc2c30) at
> ../../../gcc.gnu.org/trunk/gcc/cfgexpand.c:86
> #2  0x0837047f in expand_expr_real_1 (exp=0xb7b972f8, target=0x0,
> tmode=VOIDmode, modifier=EXPAND_STACK_PARM, alt_rtl=0x0) at
> ../../../gcc.gnu.org/trunk/gcc/expr.c:9274
> #3  0x083762f2 in expand_expr_real (exp=0xb7b972f8, target=0x0, tmode=VOIDmode,
> modifier=EXPAND_STACK_PARM, alt_rtl=0x0) at
> ../../../gcc.gnu.org/trunk/gcc/expr.c:7863
> #4  0x08376a7e in expand_expr (exp=0xb7b972f8, target=0x0, mode=VOIDmode,
> modifier=EXPAND_STACK_PARM) at ../../../gcc.gnu.org/trunk/gcc/expr.h:444
> #5  0x0836ae96 in expand_expr_real_2 (ops=0xbfffca10, target=0x0,
> tmode=VOIDmode, modifier=EXPAND_STACK_PARM) at
> ../../../gcc.gnu.org/trunk/gcc/expr.c:8150
> #6  0x08376234 in expand_expr_real_1 (exp=0xb7bb4564, target=0x0,
> tmode=VOIDmode, modifier=EXPAND_STACK_PARM, alt_rtl=0x0) at
> ../../../gcc.gnu.org/trunk/gcc/expr.c:10491
> #7  0x083762f2 in expand_expr_real (exp=0xb7bb4564, target=0x0, tmode=VOIDmode,
> modifier=EXPAND_STACK_PARM, alt_rtl=0x0) at
> ../../../gcc.gnu.org/trunk/gcc/expr.c:7863
> #8  0x083704a6 in expand_expr_real_1 (exp=0xb7b97320, target=0x0,
> tmode=VOIDmode, modifier=EXPAND_STACK_PARM, alt_rtl=0x0) at
> ../../../gcc.gnu.org/trunk/gcc/expr.c:9274
> #9  0x083762f2 in expand_expr_real (exp=0xb7b97320, target=0x0, tmode=VOIDmode,
> modifier=EXPAND_STACK_PARM, alt_rtl=0x0) at
> ../../../gcc.gnu.org/trunk/gcc/expr.c:7863
> #10 0x0826ae1a in expand_expr (exp=0xb7b97320, target=0x0, mode=VOIDmode,
> modifier=EXPAND_STACK_PARM) at ../../../gcc.gnu.org/trunk/gcc/expr.h:444
> #11 0x0826c215 in store_one_arg (arg=0xbfffd130, argblock=0x0, flags=0,
> variable_size=0, reg_parm_stack_space=0) at
> ../../../gcc.gnu.org/trunk/gcc/calls.c:4500
> #12 0x08274d79 in expand_call (exp=0xb7b46640, target=0x0, ignore=1) at
> ../../../gcc.gnu.org/trunk/gcc/calls.c:3040
> #13 0x08375088 in expand_expr_real_1 (exp=0xb7b46640, target=0x0,
> tmode=VOIDmode, modifier=EXPAND_NORMAL, alt_rtl=0x0) at
> ../../../gcc.gnu.org/trunk/gcc/expr.c:10209
> #14 0x0828cb86 in expand_call_stmt (stmt=0xb7fde140) at
> ../../../gcc.gnu.org/trunk/gcc/cfgexpand.c:2114
>
> ...
>
>
> The problem comes apparent in #5 expand_expr_real_2
>
>          if (targetm.addr_space.subset_p (as_to, as_from)
>              || targetm.addr_space.subset_p (as_from, as_to))
>            {
>              op0 = expand_expr (treeop0, NULL_RTX, VOIDmode, modifier);
>              op0 = targetm.addr_space.convert (op0, treeop0_type, type);
>              gcc_assert (op0);
>              return op0;
>            }
>
> where op0 is const0_rtx and targetm.addr_space.convert cannot recover from that.
>
> Maybe someone can help me fixing the root cause?

Doesn't make sense - in the above code treeop0 should be the

     arg 0 <addr_expr 0xb7bb449c

not the zero integer constant.

> the incoming "node" in build1_stat has already arg 1 <integer_cst constant 0>
>
> Thanks.
>
> Johann
>