On Fri, Mar 8, 2013 at 2:57 PM, Georg-Johann Lay <a...@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
>
