Richard Guenther schrieb:
> On Mon, Nov 8, 2010 at 3:39 PM, Georg Lay <a...@gjlay.de> wrote:
>> Hi, I just started playing around with named address spaces for avr.
>> Besides general space (ram), I introduced a second one, __pgm, which
>> shall address program memory where also constants may live. avr is
>> havard architecture, and both program memory and ram start at address 0.
>>
>> From this and the internals on TARGET_ADDR_SPACE_CONVERT I understand
>> that pointer casting will not work as expected, because that hook will
>> only get called if the respective address spaces are subsets. However,
>> neither is space-1 a subset of space-0 nor vice versa (or am I midlead
>> by internals?)
>>
>> Is there a way to make it work in the case where the address spaces
>> are disjoint? Started this morning and everything went smooth until I
>> started messing around with pointer casts:
>>
>>
>> char cast_3 (char in_pgm, void * p)
>> {
>> return in_pgm ? (*((char __pgm *) p)) : (*((char *) p));
>> }
>>
>> The cast looks fine from the trees perspective (excerpt from .expand):
>>
>> The first cast nullifies the pointer.
>> ;; Function cast_3 (cast_3)
>>
>> cast_3 (char in_pgm, void * p)
>> {
>> <address-space-1> char * D.1934;
>> char D.1930;
>>
>> # BLOCK 2 freq:10000
>> # PRED: ENTRY [100.0%] (fallthru,exec)
>> if (in_pgm_2(D) != 0)
>> goto <bb 3>;
>> else
>> goto <bb 4>;
>> # SUCC: 3 [39.0%] (true,exec) 4 [61.0%] (false,exec)
>>
>> # BLOCK 3 freq:3900
>> # PRED: 2 [39.0%] (true,exec)
>> D.1934_4 = (<address-space-1> char *) p_3(D);
>> D.1930_5 = *D.1934_4;
>> goto <bb 5>;
>> # SUCC: 5 [100.0%] (fallthru,exec)
>>
>> # BLOCK 4 freq:6100
>> # PRED: 2 [61.0%] (false,exec)
>> D.1930_6 = MEM[(char *)p_3(D)];
>> # SUCC: 5 [100.0%] (fallthru,exec)
>>
>> # BLOCK 5 freq:10000
>> # PRED: 3 [100.0%] (fallthru,exec) 4 [100.0%] (fallthru,exec)
>> # D.1930_1 = PHI <D.1930_5(3), D.1930_6(4)>
>> return D.1930_1;
>> # SUCC: EXIT [100.0%]
>>
>> }
>>
>> This produces the following RTL:
>>
>> ;; Generating RTL for gimple basic block 3
>>
>> ;; D.1930_5 = *D.1934_4;
>>
>> (insn 10 9 11 (set (reg/f:PHI 47)
>> (const_int 0 [0])) pgm.c:97 -1
>> (nil))
>>
>> (insn 11 10 0 (set (reg:QI 42 [ D.1930 ])
>> (mem:QI (reg/f:PHI 47) [0 *D.1934_4+0 S1 A8 AS1])) pgm.c:97 -1
>> (nil))
>>
>> ;; Generating RTL for gimple basic block 4
>>
>> So as of internals doc, named address spaces are not intended to
>> implement this kind of memory?
>
> If they are not subsets of each other how'd you convert a pointer
> pointing into one to point into the other address-space? I think
> the frontend should diagnose this as invalid.
The front end emits warning. However, explicit casts should yield only
a warning if explicit requested.
With subsets relation returning true the code is like that (I changed
the test case to add 5, the there is an additional *addphi).
;; Generating RTL for gimple basic block 3
;; D.1987_6 = MEM[(<address-space-1> char *)D.1991_4 + 5B];
(insn 10 9 11 (set (reg:PHI 47)
(subreg:PHI (reg/v/f:HI 46 [ p ]) 0)) pgm.c:98 -1
(nil))
(insn 11 10 12 (set (reg:PHI 48)
(reg:PHI 47)) pgm.c:98 -1
(nil))
(insn 12 11 13 (set (reg/f:PHI 49)
(plus:PHI (reg:PHI 47)
(const_int 5 [0x5]))) pgm.c:98 -1
(nil))
(insn 13 12 0 (set (reg:QI 42 [ D.1987 ])
(mem:QI (reg/f:PHI 49) [0 MEM[(<address-space-1> char
*)D.1991_4 + 5B]+0 S1 A8 AS1])) pgm.c:98 -1
(nil))
;; Generating RTL for gimple basic block 4
This is fine.
However, I am still confused:
"A is a subset of B iff every member of A is alse member of B".
But in this case, an element of ram is not an element of flash nor is
an element of flash an element of ram. Written down as numbers, these
numers are the same, yes, so that information gets encoded in the
machine mode to know what addresses are legal and what instruction
must be used.
Memory is not linearized because that would imply to take the decision
at runtime.
Georg
