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In the Xtensa ISA, unless the memory regions for placing machine instructions
are configured as "unified," instructions other than specific 32-bit width
load/store ones are not defined to be able to access data in such regions.
In such cases, data residing in the same memory area as the instructions,
eg., pre-configured constant tables or string literals, cannot be read using
the usual sub-word memory load instructions when reading them in units of
1- or 2-bytes. Instead, a series of alternative instructions are needed to
extract the desired sub-word bit by bit from the result of loading an aligned
full-word.
This patch introduces a new target-specific named address space "__force_l32"
which indicates that such considerations are necessary when loading sub-words
from memory.
/* example #1 */
struct foo {
short a, b, c, d;
};
int test(void) {
extern __force_l32 struct foo *p;
return p->a * p->d;
}
;; result #1 (-O2 -mlittle-endian)
.literal_position
.literal .LC0, p
test:
entry sp, 32
l32r a9, .LC0 ;; the address of p
movi.n a8, -4 ;; consolidated by fwprop/CSE
l32i.n a9, a9, 0 ;; the value of p
addi.n a10, a9, 6
and a2, a9, a8 ;; p->a : align to SImode
and a8, a10, a8 ;; p->d : align to SImode
l32i.n a2, a2, 0 ;; p->a : load:SI
l32i.n a8, a8, 0 ;; p->d : load:SI
ssa8l a9 ;; p->a : shift to bit position 0
srl a2, a2
ssa8l a10 ;; p->d : shift to bit position 0
srl a8, a8
mul16s a2, a2, a8 ;; mulhisi3
retw.n
/* example #2 */
char *strcpy_irom(char *dst, __force_l32 const char *src) {
char *p = dst;
while (*p = *src)
++p, ++src;
return dst;
}
;; result #2 (-Os -mbig-endian)
strcpy_irom:
entry sp, 32
mov.n a9, a2
movi.n a10, -4 ;; hoisted out
j .L2
.L3:
addi.n a9, a9, 1
addi.n a3, a3, 1
.L2:
and a8, a3, a10 ;; *src : align to SImode
l32i.n a8, a8, 0 ;; *src : load:SI
ssa8b a3 ;; *src : shift to bit position 0
sll a8, a8
extui a8, a8, 24, 8 ;; *src : zero_extract:QI
s8i a8, a9, 0 ;; *p : store:QI
bnez.n a8, .L3
retw.n
gcc/ChangeLog:
* config/xtensa/xtensa-protos.h
(xtensa_expand_load_force_l32): New function prototype.
* config/xtensa/xtensa.cc (#include): Add "expmed.h".
(TARGET_LEGITIMATE_ADDRESS_P):
Change a whitespace delimiter from HTAB to SPACE.
(TARGET_ADDR_SPACE_SUBSET_P, TARGET_ADDR_SPACE_CONVERT,
TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P):
New macro definitions for named address space.
(xtensa_addr_space_subset_p, xtensa_addr_space_convert,
xtensa_addr_space_legitimate_address_p):
New hook function prototypes and definitions required for
implementing the named address space.
(xtensa_expand_load_force_l32): New function that generates RTXes
that perform loads from memory belonging to the named address
space.
* config/xtensa/xtensa.h (ADDR_SPACE_FORCE_L32):
New macro for the ID# of the named address space.
(REGISTER_TARGET_PRAGMAS): New hook for registering C language
identifier for the named address space.
* config/xtensa/xtensa.md
(zero_extend<mode>si2_internal): Rename from zero_extend<mode>si2.
(zero_extend<mode>si2): New RTL generation pattern that calls
xtensa_expand_load_force_l32().
(extendhisi2, extendqisi2, movhi, movqi):
Change to call xtensa_expand_load_force_l32() first.
(*shift_per_byte): Delete the insn condition.
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